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My GF has a 2005 Buick Rendezvous. I swear this car has had more issues then any I have seen. Anyways, she was driving home from work the other night and all the sudden the heater stopped working and moments later the car began to over heat. She made it to a gas station and a couple guys put some new engine coolant in for her (Green kind 50/50).. She made it home ok after that. Yesterday she checked the coolant levels and they were fine. She then drove over to my house that night but complained the heater was blowing colder then normal. The temp gauge in the car tried to spike on her also but went right back down.. This morning I went out to look at her car before i left for work. I took off the radiator cap and the water level was fine but the coloring looked orange as apposed to green. I then looked at the 50/50 she bought and it looked green.

Is this car supposed to take a green or orange antifreeze? I have looked online but not found my answer. I do know that mixing the two is bad for the engine. Any ideas whats wrong with this car?

It sounds like the thermostat is sticking. Mixing antifreeze wouldn't cause it to do this.

Dex Cool is the orange stuff, and is not supposed to be mixed with "regular" antifreeze.
You may want to google it, I would suggest flushing it now and replace the coolant with a "mixes with all types" antifreeze.

might want to look here
http://bioengr.ag.utk.edu/ExtProg/machi ... ngcool.htm

the temperature problem is likely the thermostat.

Driver,
I would suggest that you take your vehicle to your local dealership. They will be in the best position to diagnose your vehicle for you. If you need assistance locating a dealership you can visit the Buick web site and use the Locate a Dealer tool. If you have any further questions please feel free to message me.
Thank you,
Stacy GM Customer Service

sounds to me like the thermostat or the heater core is clogged up. the heater core won,t make it overheat but the thermostat will if it,s stuck closed. yes her car takes the green stuff.