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Magical Disappearing Oil - Ford Escort

Have a 94 Ford Escort LX (1.9 Liter Engine) which have just recently replaced the engine. Replacement engine was used, but came from VERY reputable source and has ~100,000 miles on it (Prior engine had already been rebuilt once when I bought car and was losing compression). My mechanic, prior to installing, replaced gaskets, seals, timing belt and water pump. Engine has good power and gets great mileage. Problem is in two months it has consumed two quarts of oil. I drive about 500 miles in a month, so that is far too much oil usage. It is NOT smoking, the engine block is clean and shows no sign of leaks. After about 10 to 20 minutes of driving, when I pull to a stop, I can smell burning oil. This is coming through the vent system and If I get out I can smell it coming from the engine compartment. But neither me nor my mechanic can find the leak. Any ideas where the oil is escaping?

If the compression is good, the possibilities that come to mind are

  1. gumped up oil rings
  2. valve stem seals allowing oil to seep past them an night and be pulled past them at times of high cylinder vacuum (deceleration)
  3. a plugged PCV valve allowing pressure to build in the crankcase and oil to be forced out the seals

One could also put a flourescing dye in the oil, take the vehicle for a run, and look with a UV light for ;eak paths.

Exactly what to date has the mechanic done to try to find th cause?

Done a full visual inspection of the engine even up on the lift. (the engine was clean then as was when washed before shipping) Watched the exhaust for any signs of smoking, and checked the PCV valve for sticking. Ah, and when the engine was installed two months ago, it was time for the inspection, so if there was a problem then it passed the emissions test with flying colors.

If it’s not leaking then it’s burning the oil. You may not see much smoke because the catalytic converter is catching it.
Burning oil means either the valve seals, piston rings, or both.

The first step should be a compression test but even with great compression it’s quite possible to have an engine that burns oil due to stuck oil control rings.

Being from a reputable source may not mean much and the engine is still a high miles motor. It’s been my experience that a sizeable number of guranteed to be good engine/transmissions/rear axles suffer from problems in spite of claims to the contrary.