2002 Mitsubishi Galant

Check your coolant reservoir, if it's empty, add coolant to it. Then add coolant to your radiator, and rid the system of air bubbles. To do this: add coolant to your reservoir with the engine off. Once it's full, start your engine and let it get to operating temp while leaving the radiator cap removed. You'll start to see some overflow, that's normal. Then you'll see bubbles appear from the fluid soon after that. Let your engine run until the bubbles stop. Once the fluid recedes into the radiator, add more, and watch it until the bubbles stop. Do this for about 15 minutes, then watch your temperature gauge. If this does not solve your problem, check your thermostat. It may be stuck closed. Replace it if necessary (it only costs about $14). If that doesn't work, you may need a new radiator, hoses, and water pump. The radiator and hoses are the easiest to replace(you can totally do this yourself if you go to the junk yard and an auto parts store. The water pump, however, is what you'll have to go to the shop to get professionally done, as it's in a place which is hard to reach, and relies on a drive belt.

Thanks a lot. I appreciate the input. I had been told never to add to the radiator itself--only to the reservoir--but when I took the cap off and started adding, I found that it was extremely low.

I don't know why the coolant wasn't flowing from one to the other, but at least now the temperature isn't spiking.