A wicked case of blowby.

Dear Car Talk

Dear Car Talk | Aug 01, 2002

Dear Tom and Ray:

My '93 Ford F150 is spouting oil out of the dipstick, and the oil is then running down the arm of the dipstick and burning on the top of the engine. A mechanic told me it's due to the age of the engine (174,000 miles). Is there anything I can do? I live in Fairbanks, Alaska -- it gets cold up here in the winter (-25 F), and I need my truck. -- Jamie

TOM: Unfortunately, I think your mechanic is probably right, Jamie. Most likely, you've got a wicked case of blow-by.

RAY: Blow-by occurs when combustion gasses slip by old, worn-out piston rings and end up in the crankcase, where they don't belong. Actually, a small amount of blow-by is normal and is easily expunged by the crankcase ventilation system. But on old heaps (i.e., yours), worn-out rings can let so much stuff into the crankcase that the ventilation system just can't handle it.

TOM: So the pressure in the crankcase builds up until gasses and oil try to escape any way they can. And we often see air-filter housings full of oil, seals blown out or leaking, and the occasional dribbling dipstick.

RAY: The solution is an engine rebuild, which would include a ring job. But before you consider that route, or ditch the truck, I've got two other things for you to try.

TOM: If you've lived a really good, clean life, your problem might just be a plugged crankcase ventilation system. So have your mechanic check out your PCV valve and the hose it's attached to.

RAY: But even before that, take a close look at the dipstick. There's a rubber seal around the top of the dipstick that keeps the dipstick in place and keeps oil from spilling out of the dipstick tube. There's always pressure pushing up on the dipstick seal, and if your seal is no good, that could explain why the dipstick is being pushed out and the oil is leaking. And that seal can be replaced for pennies.

TOM: It's a long shot, with 174,000 miles on the truck, Jamie. But if you've helped enough old ladies cross the street in your day, a new dipstick seal might be all you need. We'll cross our fingers for you.

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