Low Oil Pressure

overthetop · May 2001

I am the proud owner of a 1990 Subaru legacy. The car has had minimal repairs, and currently has over 300,000 miles.

My oil light comes on, only when the car is running at idle. Once above 1000 RPM, the indicator comes off. I have heard that high mileage cars should consider a change in the weight of the oil they use. Could this be my problem?

adc100 · May 2001

I would get an accurate check on the oil pressure and if it's low perhaps drop the pan and check the pump intake screen. Perhaps even replace the pump??

Mr_Shiftright · May 2001

The engine is probably worn out pretty badly at this mileage. My suspicion would be the oil pump and excessive clearance in the bearings. You are way over life expectancy, so you might want to think about a rebuild. But sure, if you want to nurse it for a while longer, you could run heavier weight oil, but this is not going to overcome serious mechanical clearance issues.

If you are going to drop the pan, you should certainly put in a new oil pump, clean out the gunk and check the screen. But don't be disappointed if this doesn't help.

I think what I'd do is put in the heavier oil and also as adc hints at, put in an accurate numberical oil pressure gauge under the dash. This way you really know what you have, and you may prevent a total catastrophic failure. A light really tells you only ON or OFF...you can't foresee disaster as you can with a gradually plunging needle.

if you install a gauge and you see only 10-15 lbs at highway speeds (the red light doesn't need much pressure to go out), trouble is coming soon. So rather than seize the engine and destroy it, you could have it torn down and rebuild and possibly save the crankshaft, etc.

Another remedy is a low mileage used engine, which is about a $2,000 proposition by the time you're done.

overthetop · May 2001

Thank you very much adc and Mr Shiftright. Your insight is truly valuable.

One of my clients and friend has a service garage that I will visit on Monday. He wants me to replace the car, but there is nothing wrong with it mechanically,with the body and has never been in an accident. SOmetimes it is better to stay with the devil you know as they say.

I could replace the car easily, but to be honest I don't think I'm ready to part ways yet. I will ask for my mechanics insight as well, but will definitely install a pressure gauge as suggested.

Thanks again

Mr_Shiftright · May 2001

yep, then everybody has some quantifiable data to work with. I'll take a bet and say that your oil pressure will be lower than normal throughout the rpm range.

jgmilberg · May 2001

If you are going to replace the oil pump get a high volume unit. Melling makes a really good reliable pump. But my fears duplicate that of Shifty, bearings have had it. If you are lucky and the crank and rod are still in spec, you may be able to just do a lower end bearing job. I am not sure about your car, but most can have this done while still in the car, at a considerably lower cost. Could even have your crank ground and correct undersized bearings installed. At 300,000 miles other mechanicals have to be going as well, like the valve guides and seals, piston rings, camshaft.

If the car is in good shape body wise, and you really like it that much, a rebuild would seriously be recommended, check with your local parts store, many now have re-manufactured engines, you just need the intake and exhaust manifolds, and the other bolt on stuff, from the old engine. If that is too costly, try a bone yard, they may have one with a lot less mileage on it.

Are those miles or kilometers? I know you live in Canada, just wanted to make sure.

isellhondas · May 2001

Personally, I wouldn't open it up. 300,000 is a LOT of miles and the engine is worn out.

I wold either nurse it or have it rebuilt.

And, yes, a good used engine could make sense.

but, think of this...right now, you have a 500.00 car with those miles on it. If you spend 3000.00, you'll have an 800.00 car. If it gets wrecked or stolen, guess what your insurance company will pay you?

And cars wear out in many ways, replacing or rebuilding the engine may only be the beginning.

Now, if the miles were 150,000 I might feel differently.

orangelebaron · May 2001

You got 300,000 miles on a car with minimal repairs? Drive it till it seizes and buy a new Subaru. You got your money out of it more than twice. Once you start pumping money into it, it may never end. Just nurse it along and say buh-bye. Learn from me. Do you want to marry your 1990 Subaru?

orangelebaron · May 2001

My remanufactured 2.5 liter engine has only 18,000 miles on it. Sometimes the low oil light goes on and the guage will plummet. This will happen only at idle in Drive. If I put it in Neutral, it goes back up and the light goes out. This happens sporadically. I brought it to the shop that put the Promar engine in and said my pressure was fine. The said the sending unit was leaking and replaced it. No more low oil light for 1000 miles. Last week, the day after I get $700 work done from a different mechanic (fuel pump, clean gas tank, etc), the damn light comes back on. It kept doing it all day Saturday, but not since. Any ideas... besides "buy a new car already." Don't worry, I will.

jgmilberg · May 2001

Have the engine ground wire checked, some places don't reconnect them when installing a new engine. It could cause the light and gauge problem, among some others.

overthetop · May 2001

Hmmm....where to start.

First of all jgmilberg, the car has 525,000 KM which actually works out to more than 300,000 miles if my math is correct.

I installed a pressure gauge in my car. Started the work yesterday, and completed today. It took a while because I wanted the thing to be placed nicely in the dash,and not hanging off of it.

After spending way too many hours installing this thing, and with the help of friend who broke a few of her nails assisting me, it was installed semi-professionally (yeah right).

I am reading 10(+/- 2PSI)in idle (800RPM), 60 PSI at 3000 RPM (100km/h on highway) and 80 PSI when the engine is pushed beyond 5000RPM. Now here is my problem.... I have no idea what the hell these numbers are supposed to be, but I have a feeling that you guys do.

As a final note, someone said that the entire car is probably falling apart with this much mileage. I would love if you could actually hear the car run. It idles solid at 750-850 RPM, burns almost no oil, and has just as much power as it did when it was new (ok,...maybe a bit less). The body is fine, except for some minor rust due to our pathetic winters. I do not want to keep the car because I am in love with it...its just that it won't die! Is this such a bad thing? By the way, it still has the original muffler, and the clutch was changed at 470,000 km for the first time. As you can probably guess this car has seen nothing but highway since new. I hate traffic.

I look forward to your insight.

jgmilberg · May 2001

Different engines have different oil pressure requirements, so check your service manual. Are you taking the readings in gear? Is the light on when the new gauge reads 10 PSI? You may have a faulty sending unit for the light/gauge on the dash, with all those miles it wouldn't surprize me. I have had a few go bad on my cars/trucks, so it is not all that uncommon. If you have all that pressure on the highway, I wouldn't be to concerned. The reading is for pressure of the oil, what the oil does is lubricate, cool, and provide a "shock" cushion around all the roataing parts, almost floating them intsead of direct contact with each other, with no or very low pressure, 5 PSI or less, the parts actually rub together and cause damage to one another. So in most cases the more oil pressure the better, but not always. In really high pressure situations, you can spin a bearing, and thats really bad news. Happy motoring.

Mr_Shiftright · May 2001

I really hate to say this, but maybe the gauge isn't reading right either. Is this a quality instrument? Is it an electric unit or a direct reading one, with an actually oil line going to the gauge from the engine?

80 PSI on a hot engine at 5000 rpm? I'm very dubious.

overthetop · May 2001

I do not know the quality of the instrument, although I am somewhat suspicious myself. I bought it from a local Canadian Tire store (They sell auto parts among other things for those that don't know) for $25CDN.I don't remember the brand name. The reason why I spent so much time installing this gauge is that it is connected directly to the engine block.I had to take out the alternator to reach it properly.

I removed the existing pressure sensor and in its place bolted on the oil line that travels directlty to the gauge via a hole I drilled in the car.The oil light obviously does not come on any longer since it is disconnected.BTW, can't you have a gauge and a light working at the same time?

When I start the car I think the pressure reading is 30-40PSI. As the car warms up the reading dips to about 10 PSI. My car has a manual transmission so in/out of gear doesn't really make a difference. How exactly do I look to see what the readings should be? My drivers manual? My Chilton repair book?

By the way, right before i installed the gauge my mechanic changed my oil to 15W-50. Kind of extreme I thought, but maybe it is affecting the pressure. The funny thing was that even with this oil, at idle the oil light came on once the car warmed up.

Some insight would be great.

isellhondas · May 2001

80 lbs is a LOT of oil pressure.??

Heck, just drive the thing. What is the worst that can happen? At this point the car owes you nothing.

Most Subarus I've seen seem to get real tired around 150,000 miles.

jgmilberg · May 2001

To find the specs on your oil pressure, you will need a Chilton's, Haynes, or the factory service manual. It will give test procedures, and the like. I must have missed that 80 PSI @ 5000 RPM, but that is way high! 60 PSI is tops in most engines.

You can have both, but you will need a tee that is the same size as the threads on the sending unit and adapter. It sounds pretty tight in there, so you probably won't be able to do that. $25 dollars Canadian is not much, I think that translates to around $17 US, you flat out have a cheap gauge. Try getting one from a "hot rod" shop, look for Auto Meter, or Auto Gauge brands, they have a good reputation and are very reliable, Should cost around $35-$40 US. Try Summit Racing, they have good prices and get it to you fast. All you would have to do now is swap out the gauge.

http://www.summitracing.com

stealth1969 · May 2001

A rule of thumb for oil pressure is a minimum of 10PSI for each 1000 rpms. I don't know of a recommendation for maximum PSI. It is a basic guide when you can't find the specs for an engine.

Mr_Shiftright · May 2001

Your oil light should probably not be going on at 10psi, but that is borderline for some lights.

If you can determine that the new gauge or another gauge is accurate, I'd say don't worry about idle oil pressure at all.

overthetop · May 2001

at the Chilton manual that says my oil pressure should be 45 at 5000 rpm. Mine settles at close to 60 at this RPM.

If I buy another gauge the hose may not fit, and I may not be prepared to spend another evening in grease to carry another cable from the engine to the gauge.

BTW, the gauge has a light installed works opposite from the lighting in the dash. I used the lead from the light on the lighter but when I dim the dash lights, the light on my oil gauge increases and visa versa. Will this be solved if I switch the leads around or will I cause damage?

jgmilberg · May 2001

The gauges are pretty much standard for the tubing size. If you have an extra piece of tubing or a nut from an adapter, take it with you to the store. Does the light from the lighter dim regular with the dash? If so reversing the wires may cure the problem. Worst case is a blown fuse. You may have to find another source for the light, like the ash tray, or radio.

overthetop · May 2001

The problem is that id dims the wrong way. i.e. when the dash lights get brighter, the oil gauge dims. When I tested it, it worked properly and when everything was installed and placed in the dash,...VOILA! the opposite !! Murphy's law.

I think I'll switch them. I have some spare fuses. This source is the easiest to get to. I installed the stereo in my car, and believe me, I don't want to get a lead from there!

I did not know that all leads are relitively the same. This is what my query was I suppose. I will take your advise and take the hose to the store with me. I don't think they'll give me my money back on the old gauge w/o all the peripherals. Plus, I think I will spend the dough and get a better gauge. At this rate my gauge will be worth more than the car. Oh well, gives me something to do I suppose.

jgmilberg · May 2001

One thing I forgot to mention was to make sure the gauge is grounded if you mounted to plastic. If no it will cause the light to go funny. If mounted to metal make sure if the bulb socket has 2 wires that the black one goes to a good ground.

bobistheoilguy · June 2001

overthetop, it sounds like you have a great running engine and that what your experiencing is nothing to really worry about at this time.
as for oil pressure, at idle, you can have 5psi and that would be suffecient. hold on guys before you jump and down on this let me explain..
at idle, get out and listen to your engine, if you hear no lifter or tappet or valvetrain noise from the engine you have enough oil pressure. oil pressure can change from one type or even brand of oil to another. also from one type of gauge to another. what your doing is getting a relative reading as to if it is reading presure or if it isn't. when you get in when cold with a 15w50 i believe you said, and temp is down 20deg, you'll experience higher oil pressure than during a warmer day. so don't worry so much as to how low it is, as long as it isn't rattling,knocking or creating any kind of noise out of the norm.
now, if your up in canada, i would be careful about the 15w50, what your doing is running a thicker oil and during cold days the pumpability of that oil will be very slow. (slower than a 10w40 or 10w30 for expample). anyway, the thicker the higher the pressure, and as someone pointed out earlier, too high isn't good. what that can mean is you may have a spot in the oil channels that is collapsed down with sludge and causing a high pressure side like you have on an a/c line.
this would mean less oil flow and of course engine damage. chances are i don't think that is your problem. my suggestion about oil is one don't use a synthetic, and with the amount of miles on this engine if your consuming oil, use a straight wt oil. a muti visc oil will shear down to the lower number and pass by the rings where a straight wt oil cannot. this will improve your ring seal and help your compression a little, also will reduce oil consumption. a good 30wt mineral based oil might be what i'd consider using during the winter and maybe a good 40wt during the summer.

as for the light, well i don't know how many of you are into electronics but a light bulb is a straight piece of wire incapable of being reversed wired. either way it will light up, passing electrons through it. as one person indicated, make sure you acc light increases or decreases and since your working on that circuit, i'd suggest just spicing directly into both wires on the acc light in parrallel. just hooking up to the hot side and grounding directly may not increase of decrease if they are varying the grnd side and not the hot side.

hope this helps, and i will try and visit more often. but if you want to learn or ask more about the oil situations, don't hesitate to visit the oil forum at the below web site.

bob in jville fl.
member STLE, lubricant specialist
www.bobistheoilguy.com

alcan · June 2001

Are you serious about recommending SAE30 oil for winter use??? First, because it has the viscosity of molasses below the freezing point the engine will barely crank over. Second, it'll be so viscous on startup that highly loaded engine components (camshaft lobes and lifters/followers, main and rod bearings, etc) will be starved for lubrication and will shortly exhibit severe wear and galling.

rayfbaird · June 2001

my 1991 Subaru Loyale is getting similar readings. I get up to 80 PSI before it warms up, but idle pressure when warm hovers around zero. My mechanic is a Subaru specialist and he said that this is fairly normal for that car.

After I got a new timing belt, and replaced the cam and crankshaft seals I converted from a 10W-30 blended to a 5W-50 synthetic. I did notice a slight rise in oil pressure. It also started great in the winter.

Low Oil Pressure

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