About two months ago the car over heated on my girlfriend on her way to work, she let it get pretty hot before shutting it off, between the 3/4 mark and pegged.

We figured out the water pump was going bad, and replaced it. We bought a new thermostat for it as well, which ended up being bad. For the time being, I just cut the spring out so it would always flow. Now that it is getting cold, I went ahead and put a new one in it, but the car acts like it is still open all the time.

If you let the car sit and idle, or are driving slow through town it will get up to about a 1/4 on the gauge, but as soon as you hit highway speed, it goes down to the C. If the heater core was plugged up, I could see not getting heat inside but I don't understand why the motor loses all temperature.

 

Did you bleed the air from the system? And just because you put a new part on a car doesn't mean that the new part is any good.

 

Yeah, I agree with the thermostat being possibly bad. I'd say just swap it out again.

 

Yep, thermostat was bad. Bought a fail-safe and it failed and was stuck open. Not sure why, it never reached a high enough temp to fail.. Put a regular one in it last night, today she went about 30 miles to school and it ran normal and had heat. Should have went with my gut feeling and pulled it out sooner lol. Thanks for the replies.