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Oil disappearing!

I have a 25 year old Toyota 3.4L diesel engine that eats oil, about half a liter per tank of diesel.

Normally I might say, “well, its an old engine, must just be worn”, however I don’t have any blue smoke. Moreover, I did a compression test and it was good, so I’m surprised the oil rings could be shot if the compression rings are fine.

Now the engine does have oil leaks as it happily bathes itself from the side cover/breather/front main seal, however it never leaves spots on the driveway so its shocking that I could be losing so much through leaks.

The only secondary symptom I notice is that after using the engine to brake, like when costing downhill or to a stop without pressing the clutch, its extra smelly. (Its hard for me to tell the difference between diesel exhaust and burnt oil, so I won’t say it smells like oil… but it might) I keep trying to catch it smoking blue, but I’ve never seen it do so.

Anyone know what it could be??

I have no idea if a 25 year old diesel engine will have a catalytic converter on it or not, but if there is one it will catch any oil-burning smoke that’s being produced…at least until this makes the cat crap out.

An engine can have excellent compression readings, and yet have junked oil control rings.

I’d guess that the leaks are your problem, and perhaps they only actually leak when you’re going down the road with the engine humming along.

Check to make sure the crankcase vent tube is clear.


I checked the crank breather, its wide open (old engine has a simple tube-to-the-bottom-of-the-truck system).

No catalytic converter.

Many of the leaks will be apparent only when the engine is running at speed, with the oil pressure typically up higher than at idle. I had this problem with my Toyota 22R gas engine. I replaced the front timing seal and rear main when changing the clutch, and slowed my oil loss considerably. After the head gasket replacement at 225,000 miles, all apparent oil losses disappeared. I was back to a 1/2 quart loss between oil changes (@5,000 mile intervals).

I’d fix the oil leaks and go from there. A half of a liter is not much and it’s possible that most of it could be blown off before you even stop the vehicle.

Also agree with budd2049; it’s quite possible to have good compression, good compression rings, and seized up oil control rings.

What about valve seals? Aged valve seals could be allowing oil into the combustion chambers.

Some years ago a friend of mine who was living in Indiana for a while had a valve job performed on his old Chevy 6 cylinder truck before moving back to OK. He burned a full 24 quarts of oil on that trip (shade over a 1000 miles).
When he got it looked at back here he found out the auto machine shop “forgot” the valve seals entirely. Oops.