Can't figure out where all my antifreeze is going.

Dear Car Talk

Dear Car Talk | Dec 01, 1999

Dear Tom and Ray:

My Chevy Lumina APV uses a lot of antifreeze, but I don't know where it's going. There are no puddles under the car. I see no signs of wetness on the bottom of the
engine or transmission. I am not blowing clouds of smoke, nor do I see any signs of antifreeze in the oil. Where could it be going? I've had the cooling system pressure
tested at two different places, and it holds the pressure OK. Where is the stuff going? -- Joe

RAY: Well, the first law of industrial stoichiometry teaches us that "what goes in must either come out or stay inside." And we know it's not staying inside, ergo ...

TOM: And I would be willing to bet my brother's salary that it's coming out the tailpipe in the form of antifreeze vapor -- which isn't always that easy to see.

RAY: That's certainly a good possibility. Although it's possible that the stuff is leaking from the shaft seal of your water pump, or even from a bunch of slightly loose
hose clamps.

TOM: Even though your car has been pressure tested twice, it may not have been pressure tested correctly.

RAY: Here's the proper procedure: You run the engine until it's nice and hot. That simulates real operating conditions, when the leaking actually occurs.

TOM: Right. A lot of mechanics try to test the system when it's cold, and that's why they don't find a leak.

RAY: Then, while the engine is hot and still running, you put on the pressure tester and pump it up to 15 to 18 psi. Then leave it running a few minutes longer.

TOM: Then turn it off, and let it sit -- with the tester still on -- for two to three hours. Or even overnight. If you follow that procedure, I guarantee you'll find the leak.

RAY: And if you've lived a good, clean life, Joe, the leak will appear from the water pump, or from a bunch of loose hose clamps.

TOM: But, more likely, you have a blown head gasket, and the pressure tester will force coolant into one of the cylinders or onto the ground. We'll say a novena for
loose hose clamps for you, Joe.

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