What's causing foam to appear in this Ford's oil filler cap?

Dear Car Talk

Dear Car Talk | Aug 01, 1992

Dear Tom and Ray:

My daughter has a '89 Ford Escort with 27,000 miles on it. Every few hundred miles, a gray, foaming material fills the oil filler cap. Sometimes it has a greenish tinge. The Ford dealer has advised her to drive it harder. Does she have a serious problem?

TOM: Actually, Donald, what the dealer should have said is that she should drive the car LONGER, not "harder." Driving harder is never good for a car.

RAY: The foamy substance in the oil is probably the result of water. When excess water builds up in the crankcase, it gets churned up with the oil and ends up looking something like hollandaise sauce that's been sitting in the back of the refrigerator since 1967.

TOM: If you don't know what that looks like, just stop by my brother's house and ask him to take you on the full kitchen tour.

RAY: Anyway, Donald, this foamy stuff is not very good for the engine, because over time, the water contaminates the oil, and then you get inadequate lubrication. So the first thing to do is have the dealer check the crankcase ventilation system to be sure it's working properly.

TOM: If the crankcase ventilation system is OK--that is, it's allowing the vaporized water to escape-- then my guess is that the engine is never getting hot enough to evaporate the water. Why? It could be because your daughter uses the car primarily for short trips.

RAY: And that's where driving "longer" comes in. If she made a point of taking the car out for a half hour ride on the highway every week or two, most of that condensation would clear out, and that greenish foam would probably disappear.

TOM: The other thing you can do is change the oil more often. Obviously, the less time it's in there, the less contaminated it will get. Good luck, Donald.

Get the Car Talk Newsletter