Another wicked case of blowby.

Dear Car Talk

Dear Car Talk | Sep 01, 1999

Dear Tom and Ray:

I own an '86 Mitsubishi pickup with a 2.0-liter engine. My problem is a white,milky fluid that gets into my air filter via the valve cover. Once the air filter gets covered in this gunk, the carburetor starts to spit and sputter. Five mechanics have pulled it apart and can't find anything. Any ideas? -- Jack

TOM: I've got one, and you're not going to like it, Jack. It sounds like you've got WBB: Wicked-Bad Blowby.

RAY: That gunk in your air filter is coming from the crankcase. And it shouldn't be there. Crankcase vapors (which form this gunk) are supposed to be purged by the crankcase ventilation system.

TOM: So the first possibility is that your crankcase ventilation system isn't working (you should be so lucky). If your PCV valve is plugged up or if the hose is constricted or collapsed, that could account for the excess vapors reaching your air filter.

RAY: But more likely, there's simply too much vapor in the crankcase for the ventilation system to handle. When that happens, then the vapor can back up and contaminate your air filter, making it hard for the carburetor to get enough air (which is why the engine is sputtering and coughing).

TOM: And why do you have all those extra fumes in your crankcase? That's the WBB. "Blowby" is combustion gases that have "blown" past the rings and into the crankcase, where they don't belong. And while a little bit of blowby is normal and is easily handled by the crankcase ventilation system, when the blowby gets "wicked bad," it can cause all kinds of problems.

RAY: And the solution? This is the part you're really not going to like, Jack. If it's not a PCV valve or PCV hose problem, the solution is a ring job, a.k.a. an engine rebuild.

TOM: Have someone start by checking your crankcase ventilation system to be sure it's working. And hope to your lucky stars that it's not. Because if it is, I see major engine work in your future, Jack.

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