Evaporating Oil?

A 1990, Nissan 4X pickup, loosing oil, 1 liter every 2-3 weeks, NO smoke, NO drip spots underneath parking spot. Mechanic tried better quality oil (since in Bolivia and regular national oil is poor)with no result, no idea.

Oil does not evaporate. If your truck is losing oil, it has to be a case of worn parts such as piston rings and/or valve guide seals, a leak, or…a bad head gasket. Has your mechanic done any tests to determine if you have a bad head gasket?

The evap was a joke, the oil prob is not. Mechanic has tested compression and is ok. I will ask to check head gasket. But if is the problem, wouldn’t there be some signs to be seen? Any thing else? thanks a lot for quick response

BTW, how many km do you drive in 2-3 weeks? An engine can burn 1 liter every 1,000 km and not have visible smoke.

Does This Vehicle Have A Catalytic Convertor In The Exhaust System?
That would help clean-up the exhaust and mask the fact that the oil is burning.

Less than 1000 km, between 500-800, so could be burning without smoke as you say, but is this normal or is it due to head gasket or another possibility? Oil loss is at least 1 liter per 2-3 weeks. your instant help is appreciated, I will be at the mechanic this morning so this is great

Well, a plugged or inoperative PCV valve can increase crankcase pressure, and force oil past the rings to be burned at this rate, or back-flow through the vent pipe, and into the air intake and throttle body. It also can make seals blow out. The seals seem to be holding for now, so getting this checked is important.

Just off the top of my head, this is an 18-year-old truck, probably with 150,000 km or more on it. Using the national oil all this time has probably had an effect on wear. Even if the compression is good, oil can still seep past the rings at this rate, and be burned. I have an '88 Toyota Supra with 250,000 miles (400,000 km). It is losing 1 quart (liter) every full gas tank, with visible smoke (light) at start up that dissipates very quickly. I know it is a combination of bad valve seals and cylinder/ring wear. But compression is good, and I’m only spending $7.00 a month on oil besides oil changes to keep up. A rebuild to fix this will easily cost $2,500 or more. I’ll just keep feeding it oil until I’m forced to do otherwise.

My car used to burn a quart of oil every 1000 miles. I used an “oil system cleaner” and now my car goes all 3000 miles between oil changes without having to add oil.

I know some people will say that these “snake oils” will “damage your seals” and other crap, but I’ve used oil system cleaners on hundreds of cars - all with positive results.

In my case, the engine supposedly has an oil seal ring (on the piston) that can freeze up over time, and the oil system cleaner frees up the oil ring.