179 k miles engine burning 1 qt per 100 miles. bought used engine with 56k miles. ran fine for a week now the new (used) engine burning same amount of oil! Mechanic said compression test is good but also said he has heard the 3.5 has ring issue where compression is good but oil is getting by. Has anyone heard of this? the junk yard that sold the engine won't warranty the engine. They say it is seals, my mechanic doesn't know what to think. I'm thinking the used engine with 56k miles probly has sat for a few years and the valve seals aren't sealing now but after $4000 for used engine install not sure what to do. Mech said $1100 to remove and service heads plus parts. Has anyone run into anything like this?

 

No obvious leaks around the engine? rear main seal ok? oil pump seal ok?

 

leaks are first thing checked for. No outside leaks anywhere on the engine.

 

Wouldn't valve seals leave oil on the engine? How does the exhaust look and smell?

 

No of course not, valve seals are inside the heads and under the valve covers. IT's burning oil! Clouds of blue smoke.

 

You're thinking the valve cover gasket. If that's leaking you'd have oil on the engine and it might leak onto the exhaust exterior causing a smell but no clouds AFAIK. I think OP is referring to valve stem seals? I might be confused.

 

Change the PCV on the cam cover - that can result in excess crankcase pressurisation.

If it were oil stem seals, it should smoke badly on start-up after being left for a while and clear while driving.

If it's smoking up at idle, that's usually a sign the rings have gone.

Sound bad lcuk if it was fine immediately after the swap.