Car Doctor Q&A: Where does the coolant go?

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This week, John Paul fields a question about missing coolant that doesn’t seem to be showing up anywhere. This also happens in our bank account.

I have a 2001 usually dependable Jeep Grand Cherokee and it has been using antifreeze. I have checked all the hoses and the local shop has pressure tested the cooling system but didn’t find any leaks. The car needs enough antifreeze to turn on the low coolant light every few days. What is wrong? I love this truck and it has been unstoppable this winter and I don’t want to give it up.

A pressure test will to locate some leaks, but isn’t particularly effective looking for internal coolant leaks such as cylinder head-gaskets and cracked cylinder heads. I have found the best method is to use an infrared exhaust gas analyzer. Shops still use these testers for a variety of engine performance issues. This is simple, quick and accurate test. Simply warm up the engine and hold the end of the exhaust gas analyzer over the top of the open radiator.

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If there is combustion gases in the cooling system (indicating an internal leak) it will register as a hydrocarbon reading. The other method is to use a combustion-leak test kit. These kits use a special liquid that turns color in the presence of combustion gases. These test kits are generally accurate and can be purchased for about $50.00. One simple item not to overlook is a faulty radiator cap.

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.