I live in an area where the temp. gets as low as 10 degrees and as high as 70 degress during the winter. I am haveing a problem with the heating in the car when my water temp. gauge reads that the car is warmed up and I turn the heater on it will be hot air for a few minutes and then the temp. gauge drops down to cold again and the air gets cold. And then when I am sitting in traffic the temp. gauge will read that the car is about to overheat but when i get the car over 2,000 rpms it drops back down to normal. Also the belt squeels alot during the winter. Does anybody know what the problem might be and how to resolve it. thankx.

you don't have enough coolant in your system. The same thing happened to me and my car would overheat and i wouldn't get any hot air blowing through my vents.

I checked the coolant and its full.

did you bleed the air out of the coolant system?

run the car with the radiator cap off, topping the fluid as it goes down. you'' wanna keep doing that till the thermostat opens so u get as mcuh air out as posible

Could also have a broken thermostat. Has happened to quite a few people. Easy fix.

Sounds like air in the system. It's a big problem on the 3g's, as the thermostat is mounted a bit lower than the high point and you have to burp the system to get the air out. Friend had almost the same problem, but less severe - their car heater would work well while they were driving but would blow cold when they came to a stop. Purged it and it works great now.