Tahoe losing pressure


We have a 2005 Chevy Tahoe. Been running great. Has 140,000 miles on it 80% open road. Couple of weeks ago was highway driving and noticed the coolant temp gauge went all the way down to nothing, and then back up to normal (middle of the dial) This happened 5-6 times and each time as the temp rose back to normal, the transmission would lurch.

I took it to a mechanic who could not figure out what was wrong, but acknowledged it was running terribly. Said I needed to go to the dealer. As I was about to leave, he asked if I would be willing to gambe $20 for him to order a new radiator cap. He said that was what he would try before going to a dealer. I agreed and the car instantly seemed to be running perfectly. Now a couple of weeks later, the coolant temp gauge is dropping again. It is not going all the way to nothing, and the transmission is not lurching. It goes down from half to a quarter and then back again. So something still seems to be wrong. Otherwise all seems to be well.

If anyone has any suggestions I would be most appreciative as the thought of the cost of taking it to a dealer is making me cringe.

Thank you


You probably need a new instrument cluster

The stepper motor behind the coolant temp gauge is failing. Very common problem


If you get one of these, it’ll come programmed with your mileage

If you’re handy, you can install this yourself in 15 minutes

If you have doubts about what I said, go to a shop and ask them to sweep the gauges. That will answer the question as to whether one or more gauges are failing

If they don’t know what you’re talking about, walk away

Would a stepper motor failure cause driveablity issues? I have an o3 trailblazer that the speedometer does not work when cold, but no driveablity issues, stepper motor issue I assume. Would a failing thermostat be a possibility?


I didn’t say the stepper motor would cause driveability issues

The PCM doesn’t care what coolant temperature the gauge is indicating

It gets its info from the sensor, not the gauge

In OP’s case, it sounds like the radiator cap and the cluster were two separate issues

Thanks. I will get that checked next week. Appreciate the suggestion