Fosnot

iTrader: (15)

Go to a parts store and rent a coolant system pressure tester, pump it up to 15-20psi (don't want to go above 20, the cap should regulate pressure to 16psi max).
It should keep pressure if there isn't a leak in the system, if it does hold pressure check out the cap/overflow tank/overflow hose.
If it does start to leak pressure then bingo you know its in the system somewhere, you can rule out a few place quickly (eye the hoses, check under/behind the water pump, etc)

a10beav

The shop that did the leak down test said it passed a pressure test as well. Based on other comments here and no visible leaks, I'm going to try replacing the water pump. I just ordered one, so hopefully that solves the problem.

a10beav

I can't believe how long its been since this started, but I just solved the problem. I didn't have frequent access to the car, so that was an issue too.

Anyway, I changed the water pump and that didn't solve the problem. I did find a small gasket leak with the old pump, but I was still loosing coolant in the radiator. The only thing I had not replaced was the radiator cap, so I replaced it and that solved the problem. I can't believe I parked the car this long and changed the water pump, just for a bad cap! Oh well. Lesson learned is to do the easy/cheap stuff first...

rickybobbyss

good that u solved the problem,i was just going to say if your car has a power sterring cooler in the top radiator hose sometimes they go bad and dump coolant in to your p/s pump resivor.

wssix99

iTrader: (5)

I can't think of how you could have a bad cap that would let air in without it spewing pressurized coolant out of the system.

How many start-up cycles did you run between your pump replacement and your cap replacement?

Maybe the cap was bad in addition to something else? A bad cap could have made the initial problem worse and could have prevented the system from bleeding properly after the pump install.

a10beav

I drove it a couple times and the radiator level dropped each time. Then I replaced the cap and drove it a few times, and the level held constant with each drive. It may not be a common leak, but it made all the difference.

wssix99

iTrader: (5)

This is normal after replacing a water pump as the air bleeds out of the system. It takes a few cycles of the coolant expanding/contracting and communicating with the overflow bottle in order for all the air to work out of the system.

Old cap or new cap, you would have still had to work through the bleed cycles. The new cap might help the bleed cycle go a tiny bit faster, but it wasn't the source of your original air. (All the cap does is control the pressure and vacuum as the system pressurizes and releases/pulls coolant from the overflow. If it was bad, you likely would have experienced overheating, uncontrolled flow with the overflow, or fluid leaks.)