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Nissan Altima Engine Failures

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  • Yes, that is a tremendous about of oil to burn in 200 to 300 miles, it seems like it would make a noticable amount of smoke. It also seems like the engine would have some blowby, with that much apparent wear. Did you look at the engine pictures yet? Once you go to the photo album, you can bookmark it in your browser, to make it easy to refer back to them. I will refer to those pictures by number during the following messeges, as a picture is worth a thousand words.

    The crankcase vent hose (the hose that carries clean intake air into the engine crankcase) on the drivers side end of the valve cover, is shown in photos #07364, 07365 & 07366. Remove the spring clamp as shown, and pull the hose loose from the valve cover. You might have to take the other end of the hose loose, to get enough slack to pull it off the valve cover.

    The PVC suction hose (the hose that carries the dirty air, fumes or smoke from the engine crankcase to the intake plenium) connects on the back of the valve cover, is shown in photo #06958, you loosen that spring clamp and pull that line off the backside of the valve cover. When you pull the hose off, the hose should have suction when you start the engine, plug the hose. Look to see if any smoke comes out where you unplugged the hose from the valve cover. Having both hoses disconnected will expose the crankcase to atmospheric pressure, and it any smoke or pressure is created by blowby, it will come out one or both of the openings. A very small amount of blowby is acceptable, but a large amount is not. Having someone rev the engine may increase the smoke, if any is visible. If you do get a lot of blowby gas coming out the valve cover opening, it is an indicator that the piston rings are worn out, but confirm with a compression test. You can also do a vacuum test, but the clyinder compression test give more reliable results.

    I would not tear into or rebuild the engine without making a thorough diagnosis first, to be sure of what is wrong with it. If you are going to rebuild the engine, you will have to remove the engine from the car. It may be best to buy a remanufactured engine and put one in. A remanufactured engine from Jasper Engines with a 3 year warrenty is $3,411.00.

    You said "My intentions are to rebuild if possible or to buy another engine, but in doing this should we expect the same problems in the next 100,000 miles. Has Nissan done anything about the top cat, or should we all expect it to malfunction again. If not, it seems a fresh rebuild or new engine would be a complete waste of time and money", and you are right, you will have the same problems again, because the problem is NOT the engine, the engine is a fairly good engine, The problem IS the PRE CATALYIC CONVERTER failing and contaminating and destroying a perfectly good engine. Nissan has not done anything about the pre-cat as far as I know.
    Listen closely, read all the messeges in this forum so that you know what is going on. If you are really looking at spending that much money and that much inconvenience, it is certainly worth doing a days worth of research so that you can avoid this problem in the future. I gave you the solution in messege #190, read the BOLD TEXT again, and this time read between the lines. The catalytic convertors are required by law, so I can't legally tell you to change, alter or modify them. I can only tell you what I did. What you do is up to you. But I have permanently solved the catalytic converter problem on my daughters 2002 Nissan Altima 2.5S. It is running perfectly fine now. She has drove it about 1500 miles since I put the engine back together, and it is smooth as silk, no smoke, not using hardly any oil (she said the oil was barely down from full on the stick). Also, it is important to go back and read messege #75, and pay special attention to the part that says:
    "When I felt the 2nd catalytic converter, it was still cold, even after the engine ran for several minutes. That means it was plugged up! I unbolted the pipe and 2nd catalytic converter and took it off and unplugged it, put it back on, and the car ran perfect again."

    I fixed the converters, and I don't expect to have any converter problems or oil burning problems with it. Her converter problems were not as bad as yours, and I caught the problem in time BEFORE it destroyed the engine. Her car was starting to use about 1 quart in 1500 miles, but now it seems a lot better, will know by next oil change. I was fortunate that the Cat Plugged up the exhaust system, which brought the problem to my attention. I then unplugged the cats and the problem is gone. The reason her engine had to come apart was because the head warped and the head gasket began to leak. I removed the head, did a valve job on the head, milled the head flat, put on a new head gasket and put it back together. Take a look at the pictures of the pre-cat, photos # 06930, 06931,06932, 06933 & 06934. The inside of the pre-cat are gone, they blew down the exhaust pipe to the second cat and plugged it up. She is taking the 2002 Altima 2.5S on a 400 mile trip tomorrow, mostly interstate driving, so I will see how it did when she gets back.
    The following link is to the album on the photo site that has the photos of how the cat (second cat, the one under the car right before the muffler) was unplugged:

    http://www2.snapfish.com/thumbnailshare/AlbumID=215914481/a=85874609_85874609/t_- =85874609

    Photo #06065 shows the the second cat, the one under the car, the one that plugged up. Photo 06064 shows it in front of the muffler. Photos 06068 & 06069 show a lot of water draining out of the muffler, it was FULL of water because barely any exhaust gas went through the converter, and what little did condensed into water in the muffler, because the muffler never warmed up. Photo 06082 shows a close up of the second cat off the car. Photo 06087 shows the inside of the second cat before it was unplugged. Photos 06096 & 06097 show the stuff that came out of the cat when it was unplugged. Photos 06098, 06099 & 06100 show the inside of the second cat after it was unplugged.

    I have gone into a lot of detail in explaining these problems, because in this open forum setting, many others will read these messeges and hopefully many will benefit from them.
    Good Luck,
    E.D. in Sunny Florida
  • patpat Posts: 10,421
    Thank you so much! You are right, many will read these messages now and in the future and you are being incredibly helpful. It is much appreciated! :)
  • I just ran into the same problem. My SES light came on. I took it to Nissan and they replaced the converter. A week later it came on again and now there replacing the engine. With a used one no less.The engine was running rough and burning oil. Is this something I should worry about down the road now? My warranty expires in 1 month. I have to keep the Cats. on my car here in NJ. Should I just sell it after they install the engine, Please help.
  • jd10013jd10013 Posts: 779
    I wouldn't worry about the engine being used. an engine doesn't typically wear out, the parts inside it do. but when they say used, they mean reconditioned, rebuilt. But in a used engine block.

    If I were you, I wouldn't worry about it. Though the problem does exist, its not affecting anywhere near a majority of altima's. The chances of lightning striking twice would seem pretty rare to me. but, if your not comfortable with it, I'd sell now rather than waiting.
  • You shuld look other cars, I have a 2008 Nissan Altima SE with only 884 miles that broke down. I bought the car in December and in 44 days later the steering wheel locked. The service manager of the dealer said that a piece of a plastic bag got into the engine and wrapped around the water pump pulley and causes the tensioner to break. The dealer said that since the pieces are not defective this is no covered by the warranty. I do not understand how a piece of a plastic bag got into the engine and break down the car and I can not believe that the dealer said Nissan is not responsible for anything.
  • jd10013jd10013 Posts: 779
    you probably ran over the plastic bag. It's a freak accident that can (though rare) occur. I had to replace a CV joint on a car because of something similar happening.
  • I'm thinking of buying an '08 2.5 S but from what I'm reading with these engine and electrical issues, maybe I should reconsider. We buy cars for several different reasons but we all would want one that is reliable. What is everyone's take on the overall reliability (engine/electrical or otherwise) on the Altima 2.5 S?
  • ken75ken75 Posts: 52
    My wife and I just purchased a 2008 2.5 LS back in November and I have just put on 1K miles. Not a lot but we are retired and taking it easy. I really enjoy driving the car and having all the amenities of that model available. Most (70%) of my driving is around town and I am averaging about 23.9 mpg. On the highway I fully expect to see 30+ but we have not taken any extended trips yet and that number may be wishful thinking.
    I also am somewhat anxious about some of the posts written here but of the millions of Nissans on the road, I think it is worth the gamble to buy the vehicle. We are reading about such a small cross section of Nissan owners that the number may well be well under .01%. The car drives great, fuel economy promises to be very good, the seven year warranty we purchased should pick up most of the problems, and you will look good in the car. Check out all the threads involving the Altima and then go look at them at the dealers with any questions you have. Also check out the reviews on the 2008 Altima just to the right on this page. Lots of info there.
    Hope this helps and good luck in whatever you purchase.
  • jd10013jd10013 Posts: 779
    the altima was redesigned in 2007. the problems your reading about here mostly involve the 2002 model year, though people have had problems with models through 2006. I haven't heard of any problems with the new redesigned altima.
  • Thank you for your information, much appreciated. I took the S out on a test drive, very nice. Smooth acceleration, the seats hold you in turns and the new fuel economy estimates combined with a 20 gallon gas tank can give you plenty of miles in between fill ups. I'll know by the end of the week what car to buy.
  • Thanks jd!!! Glad to hear that it's not on the '07 and up models. That's a relief.....if I'm able to get the deal that I may be getting, looks like I'll be in an '08 Altima! Right now all in the numbers. Thank you all again for your input!!!!!!
  • The problems that we have been mostly addressing here refer mostly to vehicles with high mileage on them, usually 80,000 miles or more. The problem oil burning does not to occur in all Atimas, but seems to be more prevelant in the 2002 model.
    The Altimas themselves are lovely cars and are fun to drive. My daughters 2002 is a dream to drive, she really loves it. I think almost everyone who drives them loves them. It's just the people who have problems with them get disgusted with them, but who can blame them? Since I fixed the engine in my daughters 2002 Altima, it is again a dream to drive. It was a really nice test drive after I put the engine together, I spared it no mercy, slammed it through the gears, blasted to over a 100 mph pretty quick for just a little 2.5L engine! It drives great and handles great. They are great cars, its just a shame that some have these problems.
    I have been researching the problems with the engine, trying to figure out what the problem is or was, and this research has been ongoing, even until now. I started researching and thinking about this since September 2007, when the cat clogged up on the 2002, and I unplugged the cat. Then I went on to therorize how the oil consumption problem was related to the cat converter failure problem, and they definitely are related. Then I had to tear down my daughters 2002 in Dec 2007 due to head gasket leakage, to replace the head gasket and repair the head. I think that the head gasket problem had to do with the engine overheating more than anything else. But in the process of repairing the engine, I made sure the cats were all unplugged, and they have not been a problem since then. It seems that the oil burning is greatly reduced (I will be able to confirm this in a few months). My daughter is driving it every day, and says it's running great. My thoughts at this time is that the real problem was not in the engine, but in the defective cat, which then causes the problems in the engine. In taking the engine apart and putting it together, I was quite impressed with the design of the engine, and it seems to be built to be quite reliable.
    I have also continued my research looking at other make and models of engines, and found that the other makes also use the same type of layout and design of the exhaust and cats, and are not having these problems, which further leads me to believe the oil consumption problem in the Altimas was due to bad cats, cats deteriorating, and NOT from bad design. So it seems to me that if the cat is good and does not break down, the engine should last a long time, a normal lifetime. So hopefully Nissan took note of the problem and is putting better cats in the newer cars. The only thing is, the problem will not show up until much later, if it shows up at all. Time will tell.
    In summary, I think if you buy a new Altima and drive it for a few years, and then trade it in, you should be fine. I think the main concern should be for those used car buyers who are in the market buying 5 or 6 year old cars out of warrenty with about 80,000 or more miles on them. They may not be aware of the problem and buy the car, and then have the engine go out shortly thereafter, a very unfortunate disaster for a young hopeful buyer.
    Good luck and happy driving,
    E.D. in Sunny Florida
  • Thank you for that infomation E.D.!!! That certainly puts to rest some of the fears I had, not to mention, casts some doubt into what the salesman at Toyota was saying since he used to sell Nissan cars. I took what he said with a grain of salt because we all know the game they have to play. Either I'll like the car and buy it or I won't, the "gamesmanship" isn't necessary. So, I'm glad I came here to get some very insightful information. Just waiting to hear on the pending completed offers. Thank you all again! Maybe my next vehicle will be all electric!!!!! :D
  • jd10013jd10013 Posts: 779
    Your welcome. I' ve owned my altima a little over a year now (2007) and can honestly say its been nearly perfect. there were two recalls, 1 for the Ikey and another for the air filter that I had to have taken care of. But those were just typical glitches in a newly designed car, and nothing serious. They also were corrected for the 2008 model year. Aside from that though, the car has been perfect. rides great, handles great, is powerful (especially for a 4 cylinder), and has a ton of options standard.

    different people have different opinions and experiences when it comes to reliablitly, but this is my third nissan product. the first one, a sentra, lasted 220k miles with no major repairs, and was traded in still running. My second, a 1998 200sx, has 151k miles, I still own, is still running, and I drive it to and from work (about 50 miles per day) four days a week. in the 10 years I've owned it I've had to put 2 sets of front brakes on it. Thats it. brakes twice in 10yrs and 151,000 miles.

    those two nissan vehicles are the reason I bought my altima over a camry, accord, or other mid size.
  • let me start off by saying i'm new to this forum....i have a 2002 altima 3.5(auto) with 62000 miles...recently i have had problems accelerating when getting on the freeway or just playing around...it seems to be bogging around 3500rpm to about 4700rpm and then open back up to redline..its very annoying and i'm worried..i do have a couple upgrades like a cold air intake, exhaust and no resonators..i have heard that it can be either the mass air flow meter or tranny problems...has anyone had this problem and what do i do??
  • This is the way my 2002 Altima started with it's issues. Then the car left me stranded. Then the catalytic convertor went, then it began using 3 quarts of oil for 500 miles. I suggest you have the catalytic convertor, there are 2- a pre cat convertor near the engine and the one on the muffler pipes. Good luck.
  • oh man....thats not good...should i take it to nissan to run a diagnostic?? could it also be an 02 sensor? :confuse: .......
  • jd10013jd10013 Posts: 779
    It's not the engine, cat or pre-cat problems others are talking about. that only affected the 2.5 engine, and you said you have the 3.5. there is no oil consumption isue with the 3.5's. as for your problem, I have no idea. I have heard of CAI's damaging engines though.
  • Hi Thanks for sharing your experiences.......i have a question for you?
    I just bought a 2002 Altima in january with 90K miles and in the first week heat stopped working.......after 3 weeks i had the engine problem and thank god i had the extended warranty so they changed the whole engine.........now i am in a doubt.... should i keep the car or not? ............any suggestions.....please help
    Thanks once again
  • ASJ YOURSELF THESE QUESTIONS....HOW COMFORTABLE DO YOU FEEL WITH THE CAR? IS THE CATALYTIC CONVERTOR CHANGED? IS THE WARRANTY GOING TO STAND UP FOR ANOTHER ENGINE? DO YOU WANT TO DRIVE IN FEAR OF THIS CAR FAILING YOU AGAIN? ARE THERE ANY OTHER CARS ON THE MARKET THAT YOU YOU WOULD CONSIDER HASELL FREE? IF THE ANSWER IS "YES" TO ANY OF THESE FIND ANOTHER CAR
  • E.D. in Sunny Florida,

    Thanks for all the detailed postings and pictures. It’s nice to have you here, knowing the inside of this Nissan engine and the problems with the oil consumption.

    I have an 02 Altima I purchased new and now has 100,000 miles. Have religiously changed oil and filter between 3-4,000 miles. Have had all the recalls done at the dealership when notified. Car was good to me for five years, requiring routine maintenance and normal wear parts. No significant oil consumption.

    Mileage got into mid 90’s in late 2007, car started to run rough occasionally, like when there’s condensation in the fuel. Problem was intermittent. Used isopropyl in fuel, but that didn’t fix it. Also, the heater started blowing cool when idle, which made me think low water or weak water pump. Took to my Goodyear mechanic, a good guy and capable mechanic. Looked at computer codes, suggested changing gas cap to clear the codes and radiator cap to see if that improved the heat . He also backflushed the heater core and it got better for a few thousand miles, but it still continued to run rough occasionally for short bursts of time.

    Then the excess oil consumption started. Maybe 1 quart / 1,000 at first. Took back to Goodyear January, 2008. Replaced PCV valve, but no change in consumption. Back to Goodyear again February, checked water for trace carbon, but zero. Checked oil for presence of water but none. Compression check yielded 149, 151, 150, 149 which he thought was OK (do you agree?). Did leak down test and pressure held good. Pulled the plugs but they were dry, with a little white powder residue. Replaced plugs. Mechanic found oil in line leading from PCV valve so he replaced the valve again in the unlikely event that the new one he installed the first time was bad.

    Car is now using about 1 quart / 200 miles. Mechanic thinks he should remove valve cover to see if oil return ports are clogged, allowing oil to accumulate in top side of engine, filling to the point where the PCV is located and allowing oil to escape there.

    I decided to call the local Nissan dealer to ask the Service Manager if this problem has presented with other cars. She indicated that she has seen a couple with excess oil consumption, that the cat was the problem causing the cylinder walls to score. When I asked her if a compression check should confirm her suspicion, she indicated that it may not (what do you think?). I don’t understand this, but she’s the mechanic. She said that if the cat was indeed my problem, a rebuilt engine was the only fix.

    So, my question to you – is there any merit in pulling the valve cover and checking the oil return ports, or is it a foregone conclusion that I have the dreaded catalytic converter problem?

    I called Nissan North America to see what they know, but they won’t talk to me until I have the problem diagnosed by their dealer. They said they would entertain Goodwill Assistance, but they needed dealer-provided diagnostics first.

    Your advice, sir?
  • That was certainly an interesting post. I will try to sort some of this out for you, but some of the information you gave conflicts.
    Since you seem to have read all my previous posts, I may refer to them during this post. Your oil comsumption of 1 quart in 200 miles is horrendous, a very serious problem. Referring back to my posts about my daughters 2002 Altima 2.5S, I just recently confirmed that you oil consumption now is about 1 quart in about 3000 miles, which is very good. Before I worked on the engine and had the head rebuilt, it was consuming about 1 qt every 1500 miles. I am now supposing that the oil consumption has improved due to having the head rebuilt and having new seals installed on the valve guides. I think that most of the oil was being sucked past the valve guides. The valve guides and springs sit in "pockets" in the head that hold oil, so the top of the valve guide with the seal basically run submersed in motor oil. So it is my belief that the valve guide seals are critical on this engine.
    Another thing that struck me about your engine was that the cylinder compressions were so close together, that is a good thing. They seemed a little low to me, but otherwise good. The eveness of the readings is very important.
    Pulling the valve cover is a very simple issue, just a few screws to take out and a few hoses to remove, and a few wires to take loose. Put it back on with a new gasket to prevent leaks.
    You gave a lot of good information, but here's a few things to closely check.
    1. Check the cooling system for any sign of external or internal leaks by doing the following:
    A. Do you have to add any coolant to the coolant resivor? I have suspisions about your cooling system because of the occasional miss and also because of the heater not heating. It acts like gas bubbles are getting into you cooling system, the gas rises to the top and into the heater hoses, making less or no heat. It possible for gas to seep or leak from the engine into the cooling system, and when that happens a small amount of coolant goes into the cylinder causing a temporary miss in the engine, usually on a cold start and lasts a short time.
    B. With the engine running, watch the coolant resivor for any trace of bubbles rising inside the tank. I was able to find the combustion leak on my daughters car by doing this. If you see small bubbles that continue to rise in the coolant resivior, it may mean that combustion gas is moving out of the radiator and into the coolant resivior. These head gaskets are very prone to leakage and the heads are very prone to warp if they have ever been overheated.
    2. Check out the exhaust system completely. With engine running be sure you get plenty of exhaust gas out the tailpipes. This will confirm that either of the Cats is not clogged up. When the exhaust is cool, disconnect the exhaust pipe from the precat, at the spring connector connections, and inspect the inside of the precat, looking through the bottom opening. You should see a clean unbroken screen. If not, the Cat is shot. If the lower screen is busted or gone, then the material may have moved down the exhaust pipe to the 2nd cat, and you would be getting a service engine soon light that says bad cat. Unbolt the precat and the exhaust manifold assembly from the engine head, hold it upside down over a clean table and shake it to see if anythihng comes out. Nothing should come out. If anything comes out, the cat is probably shot. If the screens are busted in the cat and the material has moved out of the cat, you can clean out both the cats to make sure that they are unplugged. If you put it together this way, the engine will run fine, but the service engine soon light will remain lit, due to the non-performance of the cat. The precat is monitored, the 2nd cat is not monitored.
    3. Please post what codes were displayed.
    4. The compressions seems fairly good and even, but the only way to tell the condition of the cylinders is to pull the head, and that is a last resort for now. Please do what you can of what I asked in the preceeding and then we will go from there.
    Good Luck,
    E.D. in Sunny Florida
  • I have been viewing these boards along with Accord forums, closely watching both cars. My wife is purchasing either an Accord 4 cyl or Altima 4 cyl by early April. Reading these forums on both cars is getting us nervous.

    Is the same engine/cat converter set up still used on 08 4 cyl Altimas or has this engine been motified? We tend to keep our cars long term. It would not suprise me if it was the same set up since these cars would be long out of warranty.

    Any advise.
    Thanks
  • E.D - thanks for the reply. I'll answer a little here but will need time to chase the other questions.

    I suspected the head gasket at the onset of the oil consumption problem. But I instructed the mechanic to ensure this was the problem before spending the money to replace it. He did the carbon test on the coolant and found zero trace and concluded there was not a head gasket problem. I have added water to the resevoir a couple times in the past weeks, which still points to a head gasket. I will observe for bubbles as you suggets and let you know. The engine has never overheated, at least not yet.

    Like you, my mechanic also thought it was a good thing that all four cylinders had compression that was +/- 2 PSI of each other. I'm guessing he used a plug gauge, not a threaded guage, which may explain why the readings are lower than expected. I'll confirm his method and let you know.

    My mechanic also mentioned the importance of valve guide seals. If you remember, he would like to open the valve cover to see if I have a plugged oil return port that is causing the oil to accumulate in the top side and leak out the PCV valve (by the way, what do you think of this theory?). He also indicated that the valve guide seals have an umbrella shape, designed to shed oil coming from the top side, and if the oil was accumulating, the oil would rise under the guide seal and possibly escape. This sounds different than your description of the seals, which you indicate is submerged in oil. Can you say if his theory has merit? I've used him for years and he's very reputable, but perhaps he's not seen this engine torn down like you have.

    One thing I forgot to mention in the previous post, the engine oil is black, real black. It gets black very quickly, even after a complete change. And it stays black, even though I'm replenishing it with a fresh quart every 200 miles.

    How difficult is it to get the precat and exhaust manifold unbolted from the head? In the past, I've had bad luck with head bolts - they are usually pretty stuck and I'm afraid of twisting one off. I'd like to disassemble the precat and inspect it for integrity and see if any material inside is loose. And will the 2nd cat disassemble pretty easily? If either cat is shot, I'll have to replace because PA tests annually for emissions. But I don't want to replace the cat if I've already damaged the cylinder walls badly. I guess I could clean the debris out of the cats and run them "empty" for a while to see if that solves my oil consumption problem before replacing with new cats. I'm a weekend mechanic, more of a do-it-yourselfer, and not sure I should attempt to take the cats apart at home.

    And finally, please help me understand how a bad cat causes cylinder wear and oil consumption. Does a clogged cat cause the exhaust and cat chemicals to back-up into the engine? Does that corrode or wear the cylinder walls? Since I'm now using 1 quart / 200 miles, does that sound to you like it's too late to save it? And if I'm burning 1 quart / 200 miles, whether it's from scored cylinders, bad head gasket, or leaky valve guide seals, why don't I have a sooty black carbon buildup at the tail pipe?

    Thanks for taking the time to read. Hope your weather is better in FL than here in NW PA.
  • jd10013jd10013 Posts: 779
    Yes, the 08 altima uses the same QR25DE engine that has been in the altima since 2002. but you need to keep a couple things in mind, if you are seriously interested in an altima.

    1, not every altima, actually a pretty small amount, suffer from the oil consumption problem.
    2. It is almost exclusive to the 2002 model year
    3. The QR25DE engine was first used in 2002. There were, like with anything else new, some issues with it. those issues have been taken care of.
    4. then engine itself is solid. its the cat, actually the precat, that was causing the problems.

    If your not really interested in the altima, or are just looking for a reason not to buy one, then don't get one. you'll just worry about it all the time. But, If you really like the car, and are really interested in one; I wouldn't let the problems with the first year of the 2002-2006 (3rd generation) redesign featuring a brand new never before used engine keep you from getting one.
  • Thanks for asking about the weather down here, It was really nice today, beautiful blue sky and the high temp today was about 74, and they predict high of 76 this weekend and high of 80 on monday!
    I'm really busy tonight, so I'll answer the rest of your questions tomorrow.
    Many of the questions that you ask are answered in my previous posts from #75 until now.
    I'll address just one issue right now, the valve seals, and this could apply to most engines, but especially to this one. Your mechanic is saying the same thing I said, it's just your interpretation that is different. Yes the valve seals are unbrella shaped, I knew that, and 99.9% of them are, because they fit over and cover the end of the valve guide like an umbrella, this is a very normal and usual fit. But imagine if an umbrella gets submersed in water, it wont do you any good, you'll still get wet! In other words, if you are under water, an umbrella won't do you any good, unless it's seal tight around you. And as I said before, the valves, guides, springs & seals are located in pockets in the head, so the valve seal runs largely under oil, and does shed oil that falls from above it, but most of the oil is running down the sides of the pocket down to the valve guide. This valve guide depends more on the seal itself fitting tightly onto the stem. As the valve seal gets old from age and hardens from the heat, the valve stem slips up and down on the seal and the seal between the valve and valve seal becomes less of a good seal, it gets loose. Once oil can leak between the valve and the valve seal, it can reach the valve guide where vaccum around the intake valve can suck some oil through the valve guide and into the combustion chamber on the intake stroke. It takes a special tool to remove the valve springs from the head, that why it needs to be done by a professional machine shop. The bottom line is you may need valve seals, and the best way to do that is to pll the head off and get it professionally rebuilt like I had mine done, then there is no more problem. I suppose that you looked at all the pictures of the teardown and rebuild of the engine that I linked in previous posts. You can also download those pictures, they will be very helpful if you need to tear down your engine. But before tearing down anything, we need to do all the diagnostics first. I'll answer more later. Yes, be sure the oil drain pockets in the head are clear and open.
    More to come soon.
    E.D. in Sunny Florida
  • Thanks for the info on valve seals.

    A little more info for you today. I warmed the engine up today (25 degrees here) to make sure thermostat was open, then opened the water reservoir to watch for bubbling. Had to add water first because it was empty again, indicating either a leak or head gasket, correct? Had the engine running constant at 3,000 RPM, but no sign of bubbles, at least not for the 15 minutes I observed.

    Had the oil changed three days ago, so I checked the dipstick today to see its condition. It showed full, but I've only put a few miles on it. However, the oil is black again, so it's being exposed to combustion somewhere. This is the reason my mechanic thinks the oil drain pockets may be plugged. What else do you think could be causing fresh oil to blacken almost immediately after a change?

    Sure wish I could figure this out. Don't mind spending the money to replace head gasket and valve seals; just don't want to put it back together only to find out the oil consumption is still bad.

    One more item of interest. While I was observing the reservoir for bubbling at 3,000 RPM, after about five minutes, the engine suddenly went to idle RPM but did not idle smoothly. Instead it would run at idle, then run up to 1,300 RPM, then idle again. I thought maybe my prop on the accelerator pedal slipped, but it was firmly in place. I reset the prop, watched for bubbles, five minutes later, the engine did a repeat performance of dropping down to idle. Any idea why it cut out like this?

    Thanks for spending the time with this. I appreciate your insights.
  • Going back to some former messeges:

    1. "Mileage got into mid 90’s in late 2007, car started to run rough occasionally, like when there’s condensation in the fuel. Problem was intermittent. Used isopropyl in fuel, but that didn’t fix it. Also, the heater started blowing cool when idle, which made me think low water or weak water pump. Took to my Goodyear mechanic, a good guy and capable mechanic. Looked at computer codes, suggested changing gas cap to clear the codes and radiator cap to see if that improved the heat . He also backflushed the heater core and it got better for a few thousand miles, but it still continued to run rough occasionally for short bursts of time." The occasional rough running, heater running cool, and loss of coolant all point to a head gasket leak. You must check out the cooling system as I outlined in my post #214, point #1.
    "I warmed the engine up today (25 degrees here) to make sure thermostat was open, then opened the water reservoir to watch for bubbling. Had to add water first because it was empty again, indicating either a leak or head gasket, correct? Had the engine running constant at 3,000 RPM, but no sign of bubbles, at least not for the 15 minutes I observed." You said that right, having to add water to the coolant reservoir is a sure sign of a leak, and if it is not and external leak, then it is likelly a head gasket leak. I found the bubbles with the engine idling, that is the way you should check it. If it is real cold, the fans probalby wont come on anyway, if they do that means the engine reached full temperature, usually about 200 to 202 degrees, then the fans cut off when the temp drops down to about 188 degrees.

    2. "Then the excess oil consumption started. Maybe 1 quart / 1,000 at first. Took back to Goodyear January, 2008. Replaced PCV valve, but no change in consumption. Back to Goodyear again February, checked water for trace carbon, but zero. Checked oil for presence of water but none. Compression check yielded 149, 151, 150, 149 which he thought was OK (do you agree?). Did leak down test and pressure held good. Pulled the plugs but they were dry, with a little white powder residue. Replaced plugs. Mechanic found oil in line leading from PCV valve so he replaced the valve again in the unlikely event that the new one he installed the first time was bad. Car is now using about 1 quart / 200 miles. Mechanic thinks he should remove valve cover to see if oil return ports are clogged, allowing oil to accumulate in top side of engine, filling to the point where the PCV is located and allowing oil to escape there." Compression low but even, may be ok. Yes, check oil return holes in the head.

    3. "So, my question to you – is there any merit in pulling the valve cover and checking the oil return ports, or is it a foregone conclusion that I have the dreaded catalytic converter problem?" Yes, check oil return holes in the head. And you MUST check the exhaust and Cats as I outlined in my post #214, point #2.

    4. "How difficult is it to get the precat and exhaust manifold unbolted from the head? In the past, I've had bad luck with head bolts - they are usually pretty stuck and I'm afraid of twisting one off. I'd like to disassemble the precat and inspect it for integrity and see if any material inside is loose. And will the 2nd cat disassemble pretty easily?" The Precat comes off fairly easily, you need to squirt WD40 on all the bolts and threads that you will need to loosen, to help them come off, the heat shield may be the hardest thing to get off, the little bolts can be tight to get off. Once that is off, use a special oxygen sensor socket to remove both the oxygen sensors, then underneath the car, disconnect the exhaust pipe from the Precat/Exhaust manifold, remove the studs, as it makes removing the exhaust pipe easier. One of the studs was stuck tight and I had to use a torch to heat the area of the manifold near the stud red hot before I could get the stud loose. Once that pipe is loose at the front end, you can unbolt the back end of the exhaust pipe at the bolted flange in front of the muffler (it has 2 bolts with 2 nuts, very tight, use lots of WD40). Remove this pipe, it has the 2nd Cat in this pipe. If this cat is plugged or restricted, you can unplug it at this time, using a metal bar or rod and a large hammer you can knock the stuff loose out of the end of it to clear the pipe. Now back to the Precat/Exhaust manifold, Loosen and remove the bolts and a small metal support bracket at the bottom of the assembly, it connects the precat to the engine case to give the manifold some lower support. Once all that is taken loose the only thing that should be holding the manifold are the nut and studs bolting it to the head. Soak them with WD40 and the nuts should come off with no problem. The Exhaust manifold gasket is a very nice metal gasket that can be reused it you don't damage it. Once the nuts are removed, put the manifold off the studs and lift it out and check it out completely. If it is damaged or plugged, you can unplug it at this time. Putting it back on with the cat unplugged will cause the service engine soon light to come on with the code that says catalyst efficiency below threshold or simply "bad cat".

    5. "One thing I forgot to mention in the previous post, the engine oil is black, real black. It gets black very quickly, even after a complete change. And it stays black, even though I'm replenishing it with a fresh quart every 200 miles. " "Had the oil changed three days ago, so I checked the dipstick today to see its condition. It showed full, but I've only put a few miles on it. However, the oil is black again, so it's being exposed to combustion somewhere. This is the reason my mechanic thinks the oil drain pockets may be plugged. What else do you think could be causing fresh oil to blacken almost immediately after a change?" This is not a good sign, it could mean that the cylinder walls are damaged and that the rings are not sealing. The only good way to tell is buy pulling the head and actually inspecting the cylinders, checking the finish of the clyinder walls and measuring them with an inside micrometer. In the case of my daughters 2002 Altima 2.5S, I was lucky, as the cylinders looked in good shape and they were not worn. The oil consumption in my case was fixed with the new valve seals, and the head gasket leak was fixed with a head rebuild, milling the head flat and new gaskets.

    6. Continued in the next messege.
  • Continued from Messege # 220 above:

    6. "And finally, please help me understand how a bad cat causes cylinder wear and oil consumption. Does a clogged cat cause the exhaust and cat chemicals to back-up into the engine? Does that corrode or wear the cylinder walls? Since I'm now using 1 quart / 200 miles, does that sound to you like it's too late to save it? And if I'm burning 1 quart / 200 miles, whether it's from scored cylinders, bad head gasket, or leaky valve guide seals, why don't I have a sooty black carbon buildup at the tail pipe?" The chemical ceramic material (like sand) comes out of the cat and into the exhaust ports and into the cylinders and eats up the cylinder walls and piston rings, allowing oil to leak up past the piston rings into the combustion chamber and burn up with the gasoline. The oil burns clean, so you don't get much soot, I'm not sure why it burns so clean, maybe computer controls helps it to burn more completely by advancing timing and adjusting the air/fuel ratio.

    7. Finally, give me what ever information that you can, but it appears to me at this time, if you want to keep driving this car, you will need to set aside a pile of money and set some time aside out of your schedule and put your car on the calendar to do some major work on it. After everything else externally is checked out, you will need to tear down the engine and remove the head for an "Exploratory Teardown", send the head out to be resurfaced and rebuilt (New valve seals and check for cracks or leaks), And check the cylinders very carefully, lightly file the top of the engine block with a long straight file to be sure the deck is flat. If cylinders are good, you may put the whole thing back together like I did, but if cylinders are bad, the engine has to come out. Then you can decide to either rebuild that engine, or replace it with a rebuilt engine.
    Good Luck,
    E.D. in Sunny Florida
  • E.D.
    Thanks for the detailed reply. I have been off line for a couple days. I will read thoroughly and get back to you.
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