Temp Gauge Hot then Normal

[Loopy]

So this started happening last summer. On warmer days in the 70's or warmer the temp gauge would sometimes run high almost to the red for about 5 minutes then drop to normal operating temp. It would stay normal the entire time driving. Keep in mind it was not all the time. The car seem to run fine during this quick spike on the gauge. The coolant level is fine and there are no external leaks. The car also had no gauge issues this winter whiles temps were much cooler. Today the temps got above 75 today and the gauge spiked way above normal for about 3 minutes then settled back to normal. I let the car idle for a bit and everything seemed normal. Any clues what's causing the gauge to do this?

[luke_dubs]

Could be a wonky thermometer, your sensor could be bad, or you could be in the early stages of the traditional Northstar failures. However, I'm no expert.

[RJolly87]

Here is what I would do....

Check the gauge:
That era has a great many issues with bad stepper motors in the cluster. If you have a scan tool, or even can pull the coolant temp up on the DIC, check the figure reported by the PCM is consistant with what is indicated on the dash. The cluster is known to 'fake it' by putting the gauge dead center when at normal operating temps (180-220ish degrees if memory serves), but when it takes off to the red, the cooling fans should be running full bore (another indication to note). If the gauge is putting out what it's getting, I would move on to...

Check the actual coolant temperature against what is reported
In 3800s I use an IR thermometer on the thermostat housing to ballpark it. An IR thermometer can be a very informative tool when used properly as well, and can help diagnose dead cylinders, coolant flow diagnosis, etc. Once you confirm it actually is getting hot...

Check for causes of overheat
This could include cooling fans not coming on as needed, blockage, etc. Given the way you describe the behavior, I would gravitate towards the thermostat being temperamental or cooling fan issues. If cooling system maintenance leaves a lot to be desired, a full flush could be in order. Also check to see what affects it, such as sitting still, driving low speeds, driving high speeds, driving for a while, restarting warm, if running the A/C helps it, or makes it worse, etc.