It is a 1999. The temperature gauge goes up and down as I drive it. It seems to get hotter when I am driving and then it runs cold when I am stopped.

You have 2 sensors for engine temperature one tells the gauge on the dash board what the coolant is the other one ECT. SENSOR tells the computer what the temperature is.If the ECT gives the wrong information to the computer it doesn't matter what the temp. gauge reads .
It's a common problem they go bad .It works like this the hotter it gets the easier electrons flow through it. The colder it is the more residence their is because its colder and the electrons move slower through cold materials that's how it works .

Chevrolet Venture Questions - My thermostat gauge in the ...

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CarGurusOct 2, 2014 - My thermostat gauge in the car is going up and down, what could be theproblem - My thermostat starts on cold and when i get in and drive it goes from low .... low to almost hot., and it jumps back and forth when I drive the car.

Temperature gauge shot up - Bimmerforums

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Nov 30, 2010 - This morning I had a problem starting the car as it was -22F and when I finally started it my ... Now the temperature gauge still jumps right to the red zone (all the way to the right). There is no way that this is right as the engine is cold. ... Even if it were stuck closed, it would take a while for the car to warm up.

Car Repairs: Coolant Temperature Gauge - YouTube

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... Caprice/Olds Delta 88 owners. If your coolant temperature gauge isn't working, check this out before heading out to get replacement parts. ... the car is barely getting warm inside. What seems to be the problem if you know?.

My car temperature gauge keeps bouncing around from cool to red ...

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IF your symptoms are when driving , the temp gauge acts normal rising slowly. Then all of the sudden it goes high and a second or two later it goes back to normal. Then you have low coolant in the engine. The reason this happens is because of air pockets. Air pockets are much hotter than the coolant. Check for coolant leaks...

I'd say you have a faulty thermostat, be it new or not. If your temperature gauge goes to cold as your engine is taking you down the highway, the thermostat is not doing its job. The temperature should never come down to below normal until engine is shut off...

Its very possible the fan clutch has locked up and is now a direct connection from the fan to the water pump.
Depending on if it is controlled by temp or speed, it may not run at full speed when cold or at idle.
When the engine is cold and not running, a normal fan clutch would let you turn the fan blade without turning the pulley.

make sure you have plenty fluid in the radiator and the bottle. sounds like it is low.

When you said you replaced everything, did that include the temperature sending unit?
The temperature sensor just operates the cooling fan or fans for the radiator.
The temperature sending unit operates the temperature gauge in the dashboard. If that thing is faulty, the gauge won't work right.
If you did change the sending unit, it could be possible that the computor is screwing it up, but in my 41 years as a mechanic I never heard of it, when a computor goes, nothing works.

That does not seem too abnormal to me. I believe you have a 195 degree F thermostat, so you should probably be a bit cooler than 230 that is for sure. You have got an engine temperature sensor, should be located on cooling port on intake, you have a coolant temperature sensor on rad. Have you put in a new thermostat?

I'm thinking the coolnat level is low, and this might be caused by a bad head gasket - At least $800 to fix - sorry.

The sensor for the fans is in the rad at the bottom. T-stat may be bad or the rad may be clogged. Cooling system needs attention.