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Stump The Technicians--Contest Rules Are Here!

Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
edited March 2014 in BMW
Okay, this little game is meant to challenge all our Town Hall technicians (amateur and pro) diagnostic skills. Here are the rules, everyone can play:

1. Describe the symptoms of a real problem you solved or had solved, but don't tell us the answer right away--just the symptoms of the "puzzle"

2. Let us come up with answers and the reason why we think we are right.

3. Stick to problems that had definite, solid answers, not "and they fiddled with some wires and it went away". Those aren't very satisfying.

I'll start off in the next response to give you an idea of what I think would work.

best,

Mr. Shiftright
Host
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Comments

  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Okay, 1995 BMW 325, friend is driving along, and notices heat gauge is starting to climb into red.

    Friend calls me up, asks me what to do. I tell her to pull over until car cools down, then come over to see me (she is very close). She does this.

    I open the hood and notice that the coolant overflow is FULL. Temp gauge is in the red but not all the way. I see NO LEAKS. The electric cooling fan is cycling on and off every 30 seconds, but the temperature will not drop, nor will the fan stay on longer. The engine feels pretty hot to touch but is not steaming nor does it smell overheated. I couldn't check the radiator coolant level for obvious reasons. I did check all fuses and they are fine. Belt driven fan was turning, and fan clutch operating.

    QUESTION: What has happened to this car?

    ANSWER: The answer, which explains all these symptoms, can be stated in under 10 words, even under 5.
  • lancerfixerlancerfixer Posts: 1,308
    Thermostat stuck closed?
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    not bad, but usually a stuck thermostat results in a very fast, very violent overheat. Remember this just about cuts off all water circulation.

    So not the right answer, but a good answer nonetheless.
  • shiposhipo Posts: 9,148
    This board sounds like fun.

    Are we allowed to ask questions that will further enhance our understanding of a problem?

    My guess about the 1999 325i is that the engine was not actually overheating. Instead, I think that there was a problem with the Temperature Gauge or its sensor.

    If I can ask a question: what did the gauge show after a cold start, and after 5 minutes of operation?

    Best Regards,
    Shipo
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    The gauge was apparently fine when she started out, perhaps 20 minutes before the distress phone call. The heat gauge is not hard to notice on the BMW, because a red light comes on once the needle reaches red. So apparently when she started her trip the gauge was normal at cold start and steadily climbed until she noticed it near the red. That's when I told her to pullover. When she got to me, the gauge was definitely in the red, and would not drop. It was very steady and hardly moved no matter what, even with the 30 second electric fan bursts.
  • shiposhipo Posts: 9,148
    If it was not the gauge or its sender, and if the engine is truly running hot, my guess would center around the water pump (or whatever device BMW used/uses to circulate the coolant in the I6). That could include what ever drives the pump (electric, belt, gear, chain) or the impeller itself.

    Unfortunately, my days of turning a wrench are mostly over (at least for now), and I am unfamiliar with the specifics of the BMW I6 (even though I drive one myself). So, if the above guess is incorrect, I will have to demur to others more knowledgeable.

    Best Regards,
    Shipo
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    The pump was turning and the belt intact, so I did not consider this as a likely candidate (unless somehow the internal impeller had broken or eroded--a possible but far-fetched fault, so I discounted it).

    As it turns out it was not the water pump, so my decision to exclude it was a good one. I could not verify pump action because I dared not open the radiator at this time.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Can we do these one at a time? Would that be okay?

    All you have to do is cut and paste your post and save it until we're done with this one. You should also delete your post for now.

    thanks,

    Shifty
  • shiposhipo Posts: 9,148
    My post is saved until later. ;-)

    Best Regards,
    Shipo
  • isellhondasisellhondas Issaquah WashingtonPosts: 20,225
    A collapsed radiator hose? Rare, but I've seen it.
  • shiposhipo Posts: 9,148
    Low oil pressure (yeah, yeah, I know, a REAL long shot)?

    Best Regards,
    Shipo
  • shiposhipo Posts: 9,148
    How about a defective valve between the Radiator and the coolant overflow tank? It might just be that while there was plenty of coolant in the tank, the radiator itself was cooling lots of air.

    Best Regards,
    Shipo
  • lancerfixerlancerfixer Posts: 1,308
    A faulty vacuum valve (don't know the technical term) between the tank and the radiator. The fluid could check in, but it couldn't check out.

    That's a fancy way of saying I like shipo's answer. :-)
  • the temperature sensor used to control the fan.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Yes that's what I thought but then I realized the sensor must be working since the fan does cycle on and off.

    But thinking about the sensor did lead me closer to the problem, that's true.

    After the car cooled down, I opened the radiator to find--very little water! This would explain why the sensors wouldn't read properly (sensors don't read steam or air very well). But there WAS some water in the radiator.

    Soon found a crack in the upper radiator outlet, but the hose was partially obscuring this crack. I guess the water had slowly leaked/steamed out but once pressure was relieved the rest of the water in the radiator just circulated as if it were a non-pressure system.

    So mainly I was fooled by thinking that because the coolant tank was full the radiator was full. I should have realized with the crazy sensor behavior that the radiator coolant was very low. This was also why the fan could not bring down the temperature.

    OKAY--NOW FOR SHIPO'S QUIZ?
  • Shiftright is probably familiar with the vacuum fill procedure. Since some radiators sit lower than the head, some vehicles are prone to developing air pockets in the cooling system. The easiest way to solve or fill the cooling system is to put it under a vacuum and then fill with coolant. Some cars have steam bleed valves mounted on the top of thermostat housings, cooling systems will not always fill correctly by using gravity. Air pockets can and have caused engine failures.
  • shiposhipo Posts: 9,148
    My turn to take the plunge.

    In 1988, I visited a family member who I saw about once a year back then. He and I were sitting around his back yard drinking a brew when he mentioned that his motor home was having a problem that prevented it from traveling faster than 35MPH, only when the engine was warm. The vehicle in question was one of those motor home vehicles built on a full size Dodge Van chassis with a Dodge 360 CID engine, I cannot remember whether it had a 2 BBL carb or a 4 BBL one.

    The exact symptoms were as follows:
    -The engine would start easily from a cold start.
    -After the cold start, the vehicle ran just fine at all speeds for a few minutes until the engine warmed up.
    -Once the engine was warmed up, it would idle with no apparent problem.
    -From a standing start, the engine would run fairly well in first gear, however once second gear had been engaged, the whole vehicle would start bucking and shaking with terminal velocity somewhere in the neighborhood of 35MPH.

    He also told me that he had had it back to the dealer who was unable to diagnose the problem, and had even taken it to a friend who was a Chrysler Technician, who was also unable to diagnose the problem. Given that this person had a very large EGO (and I was about 20 years to his junior), I was reluctant to offer my help, however, after the third time he brought the subject up within the span of one hour, I suggested that we take a look.

    We opened up the mini-hood over the front of the engine as well as removed the engine cover between the two front seats, started it up, and started evaluating. After a few moments, I became vaguely aware that the engine note seemed to be slightly off, and I said so. He said, “You are used to car engines, this is a truck engine which has slightly different heads and a different cam.” Maybe, I thought to myself, and I started pulling plug wires starting at the #5 cylinder (which in my experience has been the weakest cylinder on the old small block Mopar engines). I pulled several plug wires off and each rewarded me with a proper drop in engine RPM and smoothness. He kept insisting that this was a truck engine and they simply run a little rougher than car engines. So, I gave up and said, “Lets take it for a spin.” Sure enough, after a couple of miles, the engine started bucking severely at virtually any positive throttle setting once in second gear.

    What was wrong with this engine?

    Best Regards,
    Shipo
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Okay, so once warm AND under load it starts bucking.

    Hmm...I'm not going to answer but I will say this could be tough, because bucking only when warm relates more to fuel issues (i.e., engine running on choke is over rich, compensating for extreme leanness when operating at normal temperature), BUT bucking under load often relates to ignition. I say under load because there is no load in first gear, but most likely there would be in a motor home in second gear.
  • shiposhipo Posts: 9,148
    I too assumed that the problem was ignition related, hence pulling the plug wires while the engine was at idle. That wasn't it. So, I tried something else, while under way (this is something that I would NEVER have been able to do with a car), I took a grounded cable and traced it along the existing wires, with negative results.

    As it turned out, the problem was not ignition related.

    Best Regards,
    Shipo
  • 0patience0patience Oregon CoastPosts: 1,712
    What was the compression?
    A valve problem?
    I've seen alot of motor homes with the Chrysler engines eat the exhaust valves and depending on how advanced it was, it may not show itself until warm.
  • shiposhipo Posts: 9,148
    Close, VERY close. The next clue should give it away.

    After testing the plug wires, I pulled off the air-cleaner (I cannot remember why), and each time the engine bucked, a 2 foot tall column of flame came shooting out of the carb (torching the arm-hair off my arm the first time it happened).

    Best Regards,
    Shipo
  • 0patience0patience Oregon CoastPosts: 1,712
    Hmmmm.
    Either the intake valve has a problem, a rocker is toast, possibly a valve spring or a long shot in the dark, the air cleaner was clogged?
  • shiposhipo Posts: 9,148
    Good job Opatience, you smoked it out. ;-)

    As it turned out, I never actually pulled all eight plug wires during the initial test when the engine was at idle; I had given up after 7. As soon as I saw the column if fire come up from the carb, I reached down and pulled the #6 wire, and suddenly, the engine seemed to be running perfectly again (albeit on 7 cylinders). When I told the owner that the #6 intake valve was burned, he did not believe me. We blew a compression test and he still did not believe it even though all of the other cylinders were ~80 pounds and #6 was zero. A year later, I was back visiting, and I asked about the engine. He said, "Wait there for a moment." When he returned, he had an intake valve in his hand which was so burned, it looked completely oval!

    A little investigation revealed that there had been a batch of motor home chassis (several hundred) complete with drive trains and instrumentation that had been sold to Winnebego (sp?) during the early 1980s, that had sat in a field (in Indiana I think) for a couple of years while the company worked itself through some financial difficulties. As it turned out, Winnebego sold many of those chassis to other builders of motor homes, many of which developed some form of engine problem (mostly valve problems) within a year or two of being sold to the final buyers. In the case of this one, if I remember correctly, the engine and chassis of this unit had been built in either 1983 or 1984, but was delivered as a 1986 vintage motor home. Two years and 26,000 miles later, and the result was the burned intake valve, and of course, by then, long out of warranty as far as Chrysler was concerned.

    Best Regards,
    Shipo
  • 74,75 sunbird. another version of the imfamous chevy vega with the aluminum block.

    here's the problem.. guy is driving it down the hwy, all of a sudden, engine dies like it ran out of gas, pull's over, hits the key, starts right back up.. go down the road again, no power loss and runs normal but, does it again in less than 1/4 mile. pull the fuel line, electric fuel pump in tank is pumping plenty of volume.

    any ideas?

    bob in jville.
  • 0patience0patience Oregon CoastPosts: 1,712
    Well,
    Do the guages all drop off? Do lights stay on when this happens?
    Is the fuel pump working when the engine dies?
    What is the voltage when this happens? Are all the connections, ground and power good?
    Just a start.
  • 0patience0patience Oregon CoastPosts: 1,712
    Ha ha. Well, I tried.
  • gauges are normal, when engine dies, oil light comes on, battery is good so is charging system. all connections and ground are good and unit will restart and run with no problems as soon as you pull over. but again, 1/4mile drive and engine dies like it runs out of fuel. connection on fuel pump is good and check vcc,(+voltage) on fuel pump is correct. read ohms across the fuel pump leads and it too is correct, so fuel pump is eliminated.
  • What aboout the coil? It sounds like it might be ignition related.
  • but, coil is good and all ignition components. when it dies, it acts like it was running out of gas. usually ignition problem due to over heating of the component would cause backfire or take a few moments to cool down before restarting. in this case, soon as you stopped, you could restart. fact is, if you were to crank it with in just a few seconds of when it dies, it would restart, but would take a second or two of turning over, like the fuel was having to be pumped back up to the carb.
  • Im a novice when it comes to engine repair (though I try real hard) sounds like a partialy clogged fuel filter or blockage before the filter slowing the fuel flow to the carb thus why it will run a little at highway speed then die out. cranking over will build enough pressure to supply fuel at low idle but at Hwy speed starve the engine?
This discussion has been closed.