Bob looks for advice on taking coolant samples.

Dear Car Talk

Dear Car Talk | Oct 01, 1992

Dear Tom and Ray:

Can I check the anti-freeze in my radiator by taking out fluid from the overflow tank rather than the radiator itself? Will the mix in the overflow tank be the same as in the radiator?

RAY: Well, Bob, generally speaking the answer is yes. The radiator and overflow bottle are connected by a hose. And the fluid--the water and antifreeze mixture--flows back and forth between the two. So it usually is exactly the same.

TOM: But despite that, no self-respecting mechanic would ever take a coolant sample from the overflow tank. First, there's always the slight possibility that the overflow system isn't working properly. Second, if coolant or water were recently added to either compartment, the samples might NOT be the same.

RAY: And third, if he does take a sample from the overflow tank, he doesn't get that macho thrill of wondering whether pressurized, scalding coolant is going to spray out of the radiator, permanently disfiguring him.

TOM: And making him look like my brother.

RAY: So while they usually are the same, the best thing to do is to take the coolant sample directly from the radiator.

TOM: And the safest way to do that is when the radiator is stone cold--like first thing in the morning. That, and good personal hygiene should keep you from ever resembling my brother.

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