Mysterious Oil Loss, 97 Tercel

Well, the saga of the 97 Tercel (manual tranmission) continues.

Review: Engine burned out due to oil leak, combined with lapse in checking oil. Engine was replaced with a used engine. Oil was then being lost at 0.7L/1000km. Valve seals were changed, which reduced oil loss to 0.6L/1000km. Oil was dripping from rear main seal, which (for some reason) was greatly reduced by changing oil pan gasket. Currently, loss is at about 0.65L/1000km. This is the approximate upper limit of acceptability according to some people, but considered quite excessive by others (and by the mechanic himself). Things that have been tried to identify the cause include:

  • Color of exhaust -- neither black, blue, nor too white (Exhaust invisible on a warm day) * No cross-contamination between oil & coolant * No loss in coolant * PCV valve changed

The mechanic has checked the following

  • Exhaust was analyzed for composition (was within acceptability) * Spark plugs have no black or white crud on it * No signs of oxidation on spark plug threads

The only outward signs of any leak is the remaining seepage from the rear main seals (leaks down face plate of transmission). Never enough to drip, but very fresh every time I see it. Perhaps the agitation of the movement of the crankshaft, combined with high pressure during operation, causes leak when car is driven, but stops when engine turned off. Seeing as it is leaking down the faceplate of the transmission, however, it could also be gear oil, but that would eliminate the only clue I have as to where the engine oil is disappearing to.

As this has been trouble-shot for many months, the mechanic plans to replace with yet another used engine. I am concerned that the engine might not be the problem, due to the lack of clues pointing that way. The replacement engine could very well be worse than the current engine, which passes compression test and leakdown test with good results (and has new valve seals). If the engine is changed, that would burn up good will with my mechanic without really solving the problem. An instructor of a basic car-care course agrees with this concern. He (and others) have checked through the engine from the top-side and from down under (car lifted) and can't find any other signs of external leakage besides the seepage down the transmission face plate.

Is it a big job to change the rear main seals instead of the engine, or is it the case that the engine might as well be changed at the same time, due to difficulty in getting the rear main seals changed?

Related question: Are there separate seals on the engine block side and the transmission side, where the two meet, or does "rear main seal" refer to a common seal for them both? If it is the former, would it be easy to change the seal on the transmission side, in case it is gear oil that is leaking?

Finally, is there anything more that can be done to track down the source of the engine oil loss?

Thanks.

P.S. Oh, yes, another possible clue is the aggravating fumes coming in the intake vent, which I've posted alot on. I believe it is coming from the engine compartment. Mostly just aggravating to lungs, throat, nasal passages, and eyes, gets very serious after a few days. Sometimes, there's not much of a smell, sometimes smells like hot oil, sometimes like burnt rubber...though it might be the case that the aggravant is separate from the smells.

Reply to
Tercel Owner
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Just an idea ... but why not.

In spite of new PCV valve is it possible that crankcase pressure is not being relieved as designed?

Such pressure could cause that drip to increase at highway engine speeds but you would only notice a slow leak when it is parked at idle. Is there a way to check the crankcase pressure - say by holding a film of plastic or a light disk over the oil filler opening awhilst revving the motor a bit?

Reply to
Leo_Lennox

I can't say that I'm that familiar with the details of the engine interior aside from illustrative concept diagrams. I tried to see how the crank case pressure might relate to the oil filler opening. Does that space share the same volume of air as the crank case? If so, how does one know whether the pressure is too high? That is, assuming that I hold a plastic film or light disk over the oil filler opening?

For PCV, I am looking at the following (as well as a textbook):

Developmental Testing of Automotive Oil Separators in the PCV System Dennis Siemiet

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p. 7 & 8 Emission sub systems - positive crankcase ventilation system Toyota
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p.2 For the oil lines/galleries, I am relying on a textbook & some animation shown in a car care course. It showed that oil gets forced up to the top to lubricate the cam shaft. I assume that this is where the oil from the filler hole goes, and there are holes in the block that drain the oil back to the pan. It isn't all that clear, however, that the space for the cams shares the same volume of air as the crankcase. Thus the reason I ask.

Tercel Owner

Reply to
Tercel Owner

Tercel Owner wrote: snip

Yes, this para is correct and the poster who suggested pressure could be right... any pressure escaping past the rings could be pressurizing the sump and if the PCV isn't doing it's job then the sump will pressurize and possibly force oil out of your main bearing seals...do as he suggests and if there does seem to be quite a bit of pressure there try changing your PVC again.

Reply to
Gord Beaman

Okay. Will give it a go. Just not sure how to recognize too much pressure.

Reply to
Tercel Owner

My car was burning oil but it was obvious from the exhaust cloud. The problem was intermittent - sometimes blue smoke for a 10 km trip and other times there would be no problem on the same trip.

The problem was an obstructed crankcase ventilation system - sometimes becoming unobstructed. (My car has no PCV valve.) Frothy oil had plugged the breather hose and a condensation chamber. This scummy foam was also evident on the underside of the oil filler cap.

A failed ventilation system will allow pressure to build up in the oil pan and the valve cover. In my case, we speculate that oil was being forced upward past the (worn) piston rings and burning in the cylinders.

Cut out a smooth piece of cardboard to amply cover the oil filler opening. Slobber it with oil and hold it lightly over the oil filler opening. Check whether the cardboard is pushed up or whether air is being forced out of the opening.

Reply to
Leo_Lennox

Well, to be honest, neither do I...I'd sort of think that there shouldn't be any pressure there to speak of though.

Anyone else here who might know?...Philip?...failing this, you might ask a friend with a similar vehicle to do this test and compare results?...

Reply to
Gord Beaman

I'm the odd ball. Most people I know have American cars. I'll give it a whirl anyway. Thanks.

Reply to
Tercel Owner

Well, I haven't seen any frothy oil under the filler cap. I'll give the oily cardboard a try. Thanks.

Reply to
Tercel Owner

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