What's the cure for condensation on my distributor cap?

Dear Car Talk

Dear Car Talk | Oct 01, 1999

Dear Tom and Ray:

Our 1988 Pontiac LeMans is a piece of junk, but there's no way we can trade right now. The problem is condensation in the distributor. Almost every day I have to take
it off and wipe it out to get the car to start; then it starts for the rest of the day. I've tried the spray, but that doesn't work. George, an 80-year-old ex-mechanic, says to
put a plastic bag over it, but common sense tells me it would collect even more moisture, not to mention melt all over the engine. Someone else said to drill a hole in the
cap. What do you suggest? -- Clyde

TOM: I'd check the supermarket, Clyde. I saw an ad that says Hefty has Sandwich Bags, Freezer Bags and now, "New, Distributor Cap Bags"!

RAY: Actually, the guy who said to drill a hole is closer to being correct than George is with his bag theory. I'll tell you a little story. We had a customer some years
ago who drove an old Dodge van. And every three months, he'd come in because the van was running terribly.

TOM: And we'd take off the distributor cap and, sure enough, there would be so much moisture in there that mushrooms were sprouting on the inside of the cap.

RAY: So we got fed up one day and put on a new cap and sealed it with a whole tube of waterproof silicon sealant. We put so much goop on there that, when we were
done, not a molecule of water could have possibly gotten inside. And we patted each other on the back and sent this guy on his way, confident we would never see him

TOM: Well, three months later he was back, and the problem was exactly the same. It turned out that the moisture wasn't coming from outside the distributor, but from
inside. The distributor shaft was worn out, and moisture was coming right up that shaft from the engine. So, in effect, we made things worse by sealing all that moisture

RAY: And what almost all manufacturers have done since then is come out with vented distributor caps. The vent looks like a little smokestack with a cover on the top --
kind of like a chimney cap on a house. It's designed so that moisture can get out, but can't easily get in. And that's what you need, Clyde.

TOM: You should go to your local auto parts store and see if someone makes a vented distributor cap for your '88 LeMans. And if not, you can craft one yourself by
drilling a hole and using the covered vent from another cap. Good luck, Clyde.

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