I have a 2005 Toyota Corolla with 303,000 miles on it, impressive, right? Anyway, I fill the radiator with coolant and it quickly disappears. Like within driving it for a day, I wouldn't say it all leaves the system but it definitely shouldn't be emptying that soon. I can't see any external leaks which leads me to believe it is disappearing internally. Any thoughts on why?
Pressure test and/or use UV dye to look for leaks, and test your head gasket for failure.
Use a coolant pressure tool and boost it to around 18 PSI and let it sit for around 15 minutes. If it noticeably leaks and there's no sign of anything on the ground, get a head gasket tester, let the engine cool off for a few hours, then pull a couple inches out of the radiator. Leave the radiator open, start the car, wait a few minutes, then start pulling gas through a special fluid that's meant for testing head gaskets. It should remain blue after a few minutes. If it turns yellow, you have a blown head gasket.
I tested my car for head gasket once. It’s not too hard to do. You’re basically finding out if there are exhaust gases in your coolant. If so, you’ve got a head gasket issue most likely (and you could be losing coolant to the engine). I borrowed the block test kit for free from Auto Zone, I just had to buy the bottle of block leak test chemical. The colors and more details about the test are noted in the response above
