CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Puffy Montero

I have a mysterious exhaust issue on my 1991 Montero. After the engine warms up and I have been stopped at a red light for a minute or so when I accelerate away from the light a cloud of blue (I assume oil) smoke puffs out of the exhaust pipe. If I sit in the vehicle with it idling for, say, 5 minutes then the cloud of blue smoke can last all the way down the block. Then it goes away. Spark plugs are all clean. PCV valve recently replaced. Mo warning lights. What can this be?

I think that oil is being sucked in around the valve guides. You may need new valve stem seals.

Do you also smoke when decelerating or going downhill?

Sounds like valve guide seals to me also. If it was bad oil rings the smoke would not go away.

Could be clogged oil drain holes in the head.

How many miles are on the car?

Valve stem seals.
Your engine’s pistons fill with air & fuel by pulling it in past the throttle body every time they go down the cylinder with the intake valve open. When the engine is sitting and running with your foot off the gas, the throttle plate is closed, and a vacuum is created by the piston going down. That vacuum can draw oil past worn valve stem seals, which are the only things that normally prevent the oil used to lubricate the valvetrain (camshaft etc.) from being regularly drawn down into the cylinders.

In addition, over time the rings around the piston that wipe the cylinders down and prevent excess oil from remaining there to get burned in the cylinders lose their spring tension over time. That combined with wear on the cylinder walls and the rings can allow too much oil to remain on the walls after the pistons pass down and that gets burned. That may be exascerbating the problem.

The car is over 21, old enough to smoke in 50 states. I’d suggest a good evaluation of the condittion of the engine before considering replacing the valve stem seals.

The car has 148,000 miles. The compression is good so I’m figuring that the rings are good. The problem started when, in an effort to quiet a noisy lifter, I added a can of Risoil. Could this have loosened up the old gunk that was around the valve stems thus creating a problem where there wasn’t one in the first place?

Did you change the oil afterward? It may be a good idea to get the additive out of there. If your oil level is too high, you might get oil burning that wouldn’t happen if the oil level were normal.

It’s possible, but I’m inclined to think it was a coincidence.

It’s truely great that the compression is good, but remember that the valve stem seals are rubber. 20 year old rubber.

As it turns out, I think we were all “overthinking” this problem. I took her out and put about 1000 miles of 65mph highway driving on her and the problem has disappeared. As far as I know this vehicle hadn’t been driven outside of the city limits (30 mph) for 10 years. (So maybe there’s some truth to Grandpa’s advice that a car NEEDS to be run “wide open” every once in a while. Thanks for all your advice, guys.