99 tahoe with the 5.7. In the lasr week when i take it out the temp gauge raises to the the red line check gauge light comes on. It hits red and then just a minute or so it drops back down to normal temps. I replaced the thermostat a few months ago and havent had this problem till now. Would a thermostat go bad after a few months? Anything else to look at? Thanks

 

Do you have antifreeze in the system or all water? If it is water then you also have rust in the system. I have seen thermostats go bad in a few months especially with rusty water.

 

Some t-stats can be bad out of the box. Sounds like yours was stuck shut and then opened.

 

Yes i have antifreeze and water in the system... Im going to check everything tomorrow and yank thevthermostat and test it on the stove

 

did you properly bled all of the air out of the cooling system? it might have a "hot spot" in the system. make sure you have all the air bled out of the system and check the temperature sensor and the gauge.
on my suburban the gauge is actually bad... instead of swapping the gauge cluster out I just put in an aftermarket coolant temp gauge and it works fine. the gauge itself was bad.

 

99tahoeinwv,

When you start filling the Radiator to get things going again, MAKE SURE you turn on (all) the Heaters for the cabin where any air will be replaced with Coolant. Then, after you close the system for use, check the Coolant level the next morning before you start your vehicle. It may have "burped" and dropped down and need to be added to.

 

yes they can be bad right out of the box ,i had a new one in a engine i just put together ,it did the same thing .new one ,no problem .