94 Camry radiator doesn't pull coolant from overflow tank

Why would the radiator in my 94 LE (247k mi) not pull coolant back into it from the overflow tank. Every few months I have to add about 20 ounces of coolant to the radiator. Hoses from radiator to overflow tank and one small one off the overflow tank are clean, no blockage, and when presurrized, will not leak air. My radiator cap is pretty old but seems to not leak, etc. Should I replace it anyway or could the problem be somewhere else?

I would replace the radiator cap with one from Toyota so that you are sure you get the correct pressure. They are not that expensive you have to take a chance with an aftermarket one.

When you said that "when presurrized, will not leak air.", did you mean the overflow tank and hoses or the entire cooling system. If you haven't checked the cooling system, do so. There may be a leak there. Still, the most likely cause is the radiator cap.

I agree, it sounds like a bad cap that can't vacuum the coolant during cool down period.

Thanks. I pressurized just the hoses to/from the overflow tank and tank and no leaks, blockage. I will try a new rad cap though. I did have a total shutdown from an overheat and total loss of coolant from my waterpump/timing belt area about 35k mi ago. Although my mechanic did replace the waterpump, timing belt, and t-stat he did say that I may have caused irreversable damge to the heads, other components that may get worse in a few months or a few years. I think I may be knocking on that door now. Hopefully the cap does the trick. If not, I wil get the whole cooling system pressure tested.