Newbie with a Cooling system problem.
 

This 944 has a thermostat reading continues to raise to the bottom of the red stay there for a while then drop to the middle, then work its way back up to red and then drop right back down.

Can you verify that your radiator fan(s) are turning on properly?

Also, is the system is not bled properly, an air bubble trapped in the cooling system could cause this.

Did you open the coolant reservoir while it was still hot? This will definitely cause it to overflow, as it is pressurized. If thats the case, and you popped the reservoir cap while hot, there is a likelihood that some air was introduced into the system at that point as well.

thank you, thats what i thought was the issue... air bubble. The fans turn on when the car is off i know that. I am not sure if they turn on during driving.

Do you just suggest draining the coolant system and refilling with a new mixture of coolant and water?

just to be safe i will get a new termostat and flush the coolant system. That should take care of it. I know that the thermostat could be an issue as well.

ifs its a new-to-you car, and you're unsure how long the coolant has been sitting in the engine, myself, I'd flush and fill.

Depending on how hot it is where you live right now it might not be so abnormal. I had the waterpump update, new thermostat and fluids. In hot weather, in traffic especially, air conditioning on, my car would do the same thing. It never caused any problems, was more annoying than anything else.

Sounds like your fan switch is working.... if you dont want it to run so high, you could switch to a lower temperature fan switch.

Yeah in 2003 i got a new thermostat, a new water pump and head job. Today it was hot out and i was in traffic, but on the freeway it still would climb and drop.... climb drop... climb drop. It has to be the air bubble.... COME ON AIR BUBBLE. NO WAMMY.. NO WAMMY STOP! I hope thats all thats the problem.

My buddy with an 86 944 said that he fixed his overheating issue with a oil cooler gasket? (cause his oil and coolant was MIXING! I doubt its that issue)

I read a few articles describing the coolant and oil mixing being a common point of failure on 944's. I never experienced that, you might want to try turining the heat on. The flow to the heater coil may help to flush the bubble out, it might not work but it's an easy thing to try, good luck..

Fro the Thermostat in the car, you may want to replace it with a 180 degree t-stat. My car barely hits 1/2 on the hottest of days. Also, it's a main in the ass to change. It took me 4 hours to get it out, and 15 min. to replace. It's molded into the side of the water pump and held in with a MASSIVE C-Clip. Make sure you have 90 degree bend snap ring-pliers for this.

For the coolant, I'd replace it just in case. To bleed it, get the engine warm so it circualtes, then find the bleeder screw on the top of the engine and SLOWLY crakc it open until it lets pressure out and it'll bleed itself. Once it stops spewing air/coolant and switched to just coolant, it's ready to go.