Did leaving the radiator cap off do any lasting damage?

Dear Car Talk

Dear Car Talk | Jan 01, 2000

Dear Tom and Ray:

I took my car in for an oil change, and a couple of hours later the temperature
gauge started to go up. I drove a short distance to a gas station as the
temperature continued to climb toward "H." I popped the hood and saw a small
amount of smoke. The mechanic came over and noticed that there was no radiator
cap. Since I drove quite a distance before the car started to heat up, I suspect
it just wasn't put on tightly enough and fell off somewhere along the road. I
called the guy who did the oil change and he said to send him the bill for a new
radiator cap. The car seems fine, but now my other concern is whether any other
damage was likely done. What do you think? -- Monique

TOM: I doubt any damage was done, Monique. Normally, we tell people to shut off
the engine immediately if the car is overheating (unless you're someplace unsafe,
like in my brother's neighborhood, in which case your well-being is obviously
more important than the engine's).

RAY: But since you got to the gas station and shut off the engine before the
needle ever got to "H," I think you're going to be fine. So I'd just keep driving
and forget it ever happened, Monique.

TOM: Easier said than done, I know. Every time there's a new lipstick stain on
the passenger seat, you're going to wonder if was because of "that time the
radiator cap fell off," right?

RAY: Well, to put your mind at ease, have a mechanic you trust do a "head gasket
test." That's a simple test he can do that will tell you if there's any leakage
between the cylinders and the water jacket. That's the problem most likely to
occur on a car that's been severely overheated. If he says it's fine, then you're
home free.

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