temp guage goes wild

Hey Guys I got a 2000 Venture that the temp guage wont move but very little then jumps to the red and the motor slowes to 20 mph. for about 5 miniuts then when the guage drops back to cool the motor acts normal.
The low coolant light comes on just before it jumps to hot than I get a hot coolant light and the needle jumps to the red and then back to cool. i open the radiator cap when cool and get a pressure release and then it runs normal until I hit a bump then it jumps to hot and the same thing again.

I replaced the thurmostate and the waterpump and it didnt help a thing. I thought it was a faulty guage or sensor and replaced the sensor but still nothing changes. Although I noticed there is no heat inside the vehicle

Hey Guys I got a 2000 Venture that the temp guage wont move but very little then jumps to the red and the motor slowes to 20 mph. for about 5 miniuts then when the guage drops back to cool the motor acts normal.
The low coolant light comes on just before it jumps to hot than I get a hot coolant light and the needle jumps to the red and then back to cool. i open the radiator cap when cool and get a pressure release and then it runs normal until I hit a bump then it jumps to hot and the same thing again.

I replaced the thurmostate and the waterpump and it didnt help a thing. I thought it was a faulty guage or sensor and replaced the sensor but still nothing changes. Although I noticed there is no heat inside the vehicle
Welcome to the forum!

Sounds like you have air in the system or you are low on coolant (or both). Did you bleed the air out of the system when you changed the parts? Bleed via the brass bleed valves near the water pump and thermostat.

Let us know what happens.

Take Care,

Are you adding coolant constantly? All the symptoms you describe is indicative of air in the system. As already mentioned, release trapped air via the brass screws. If you have done this several times already and/or you are adding coolant constantly, you might want to investigate a coolant leak or head gasket issues.

-The low coolant light comes on
-jumps to hot
- hot coolant light
-needle jumps to the red and then back to cool.
-open the radiator cap when cool and get a pressure release
-I replaced the thurmostate and the waterpump and it didnt help a thing.
-replaced the sensor but still nothing changes.
-no heat inside the vehicle
All symptoms of head gasket failure (specially when they all come together). Exhaust invasion of cooling system. forum is full of similar events. It is alas a fact of life with the 3.1/3.4..and , to be fair, with a LOT of other modern engines too, specially those using dissimilar block and head material. Latest example in my backyard: Subaru Outback (To show how common it is, Outback owners are even contemplating a class action)