Cruise/temp relationship

[mark315]

I have a 2007 sedan. A couple of weeks ago my temp gauge was rising while on the highway. I brought it to my mechanic and he tested it and said there was no indication of it overheating. Yesterday while making the same trip it did it again. Now I know this sounds crazy but it seems that the temp gauge only rises when I'm using cruise control. If I turn it off the temp goes back to normal. When the temp rises it doesn't get to a critical level. Usually about 3/4 of the way to Hot.
Can anyone provide insight? The thermostat is about a year old. Coolant is new.
Thanks

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[CBXBob]

Sounds like an indication/dash problem. anything else affect it? heat lights ect. try driving in test mode and monitor actual temp. Just a guess.

[whynotthinkwhynot]

Could be dash problem, could be wiring problem. I would double check the issue using the electronic odometer trick. Key off, press and hold the trip odo reset button, turn key on, continue to hold reset button until the odometer reads [test], release button. Now each time you press and release the odo reset button you will scroll through one of 30 test functions until the key is turned off again. There are too many to go through, but a few of the first ones might interest you in the future- like the [bat 12.1] bat/alt readout. You are looking for one that reads [15 C] or whatever your temp should logically be at the time in C. Now start the engine, and drive the car. You should see the temp moving up towards 92C where the thermostat opens, then dropping down, over and over again until it reaches a stable temp somewhere around 110C. The electric fans should come on at 115C low speed, and 118C high speed, but will only come on at low mph.

Now test your theory. It should be interesting to see what the temp goes up to. Someone more technical than I can tell you what the temp jump means. I'd say a wiring fault under the hood. Possibly something melted or maybe just corrupted like at the bulkhead connector if it got water in it.