No signs of my leaking coolant...

Dear Car Talk

Dear Car Talk | Feb 01, 1990

Dear Tom and Ray:

I have an '81 Buick LeSabre and I have to fill the bottle up with coolant every few months. The radiator is full and I don't have any leaks. Where is it going?

TOM: Were you paying attention in Industrial Stoichiometry class, Pam? If you were, you would know that "what goes in must either come out or stay inside."

RAY: Don't worry, Pam, I learned the same lesson watching the door to the men's room here at the office last week. But the point my brother is making is that if you're losing coolant, it has to be going somewhere. And even though you may not see a puddle on your garage floor, that doesn't mean you don't have a leak.

TOM: You could have an internal leak or an external leak. An external leak from a hose or water pump could be so small that the coolant will be forced out only when the system is under pressure (e.g. when the car is running). Rather than leaving a tell-tale puddle on your garage floor, you may be leaving a puddle 6 miles long and a nose-hair wide between your home and work. To find a leak like that, your mechanic would have to pressure test the system. And if the leak is as slow as you say it is, the car may have to be observed for several hours in order to find it.

TOM: If your mechanic doesn't find an external leak, the coolant must be leaking INTO the engine through a blown head gasket, cracked head, or cracked block. If coolant is leaking into one of the cylinders, it's being vaporized and coming out the exhaust pipe as a white cloud. If it's leaking into one of the oil passages, it's mixing with the oil. To test for that, pull out the dipstick. If it looks like that cup of cafe-au-lait that's been sitting on your desk for the last four days, you've found the problem.

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