My daily commute mainly consists of a 10 mile, 3500' elevation gain stretch. On the return trip I coast in 3rd gear (97 OBW, automatic, 208k mi). When the grade levels out for the last 2 miles, I put the tranny in D and hit the gas. The car burns oil for the entire 2 miles (I can see this in the rearview). This is the only time the car burns oil like that; otherwise, it burns very little. Any insight as to why this is happening? Thanks for the help...

Descending a hill is a condition when the throttle is closed, intake vacuum is high, and combustion chambers cool down. Oil gets past rings, and especially past worn valve stem seals, and doesn't get much of a chance to burn off. When you level off and open the throttle, you're moving a lot more through the engine and the combustion temps go up, burning off the accumulation. Bingo, instant smokescreen.

Just for the heck of it, when was the last time the PCV valve was replaced?

 

nipper

Just for the heck of it, when was the last time the PCV valve was replaced?

Good point, Nipper -- a clogged PCV (valve and/or hoses) can allow the crankcase to pressurize and increase the likelihood of the problem.

Good point, Nipper -- a clogged PCV (valve and/or hoses) can allow the crankcase to pressurize and increase the likelihood of the problem.

 

Agreed, back in the old pepper tree mechanic days ... before any pollutiion devvices had been invented (even the PCV valve), I was always taught blue smoke on acceleration = rings, blue smoke on deceleration = valve guides.

 

In this case, I too voe for a clogged PCV valve.

Just for the heck of it, when was the last time the PCV valve was replaced?

 

nipper

 

Bingo. I would bet ten bucks it's the PCV valve. Get a genuine SOA one as the aftermarket ones are crap. This is a very common problem in Subarus of pretty much every generation.