Where did my antifreeze go?

About six weeks ago my temp guage indicated that I was running hot. I found that I was low on antifreeze, about a gallon. Recently I added another gallon. I took it to the shop and they did a pressure test, a hydrocarbon test, checked for leaks, also no indication of water in the oil and none on the driveway. Does anyone have any other ideas?

The only thing I can think of would be, possibly, a breach in one or both of the head gaskets. I have an old Mercury Sable with a coolant habit and no apparent cause of it. I have never let the car get hot or run low on coolant, and it just started doing it about three months ago. I also have not been able to find a reason for the consumption, so I assume it has a breach in a head gasket due to age and mileage of the car (14 year old car with 135k miles). The difference between our situations is that, apparently, your car is consuming much more coolant than mine. My car uses a quart a month, yours a gallon every three weeks. Whatever it is, it will likely become very apparent very soon, so keep a close eye on your coolant level, and pray it’s not head gaskets or worse!

thanks for the input

The first thing I’d do is change the radiator cap. They’re cheap, even for your Rover, and they can cause all sorts of odd problems when they go bad.