Blowby: the beginning of the end for this engine.

Dear Car Talk

Dear Car Talk | Oct 01, 2004

Dear Tom and Ray:

My wife drives a 1991 Ford Escort. About every six weeks or so, I have to replace the air filter, because oil builds up in the box that holds the air filter. No mechanic to date has been able to solve this problem. Any suggestions? -- Michael

RAY: I'm surprised no other mechanic has been able to fix this, Michael. It's very simple. You just change one part, and this problem will completely disappear. Unfortunately, that part is the engine.

TOM: You have what we call "blowby." That's when combustion gases from inside the cylinders sneak by old, worn-out piston rings and get into the crankcase, where they don't belong. Soon, there's too much gas and pressure in there for the crankcase ventilation system to handle, so, to relieve pressure, oil gets blown back into the air-filter housing, where it ruins your air filter.

RAY: Assuming your crankcase ventilation system is working, blowby is basically the beginning of the end for an engine. In your case, maybe the middle of the end. But the good news is that you won't do any more harm to the engine by driving it. So, you can keep driving it until it dies, thereby creating a severe air-filter shortage in your region.

TOM: If this car were something spectacular -- you know, like a '95 Escort -- I'd suggest that you look into a replacement engine from the junkyard. You can do that if you're unnaturally attached to this car.

RAY: But keep in mind that a replacement engine will cost you at least $1,500 when all is said and done. And for that money, at 10 bucks a pop, you can replace the air filter every six weeks for 17 years. Good luck, Michael.

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