We purchased this vehicle 3 months ago, which has only 70,000 miles on it, and have added over a gallon of coolant since. However, there are no external signs of leakage. We have been told it could be a cracked cylinder head with fluid leaking into the combustion chamber. However, there is no evidence of the coolant getting into the combustion chamber. Compression was fine and so was the block test, and no engine light, or fault codes have come on. I'm just curious if anyone else has had a problem with this and if there is an accurate way to make a diagnosis. -Thanks,
RT

 

If you had a coolant leak in the engine, most of the time anyway, you would have white smoke out of the tailpipe. I would assume you looked at the bottom of the water pump to see if the weep hole is leaking? If so, the only other thing to do is a pressure test on the radiator. Either rent a pressure tester, or have a shop pressure test it for you. If you have an automatic trans, you may have a leak inside the radiator between the trans cooler and the coolant side. Either way, pressure testing should help find the leak, either by hissing sound, or bubbling. A gallon of coolant over a 3 month period is not alot, so your leak is a very small one at best, and those can be a real b**** to find sometimes. Also, usually with a block problem, coolant will burn and go thru the exhaust, contaminating the O2 sensors, and throwing a CEL, you said you hadn't had a CEL, so I agree that this is probably not your problem. With such a small leak, you will not have "wet" signs of the leakage, but you may see dried "tracks" of it, a place where it looks like water had been but dried up? Kinda hard to say for sure w/o seeing it myself, but it sounds like your on the right track. As a mechanic, my next, actually my first, step would be to pressure test the coolant system. Hope that helps, and Good luck!