A week ago I got the oil changed. On the drive home, I notices my temp guage registering an uncomfortably high level (265 is the top line, it was at that top line). No boiling over at all or anything, but I threw on the heater on high and got home quick. I have now replace the thermostat (which appeared to be fine) with a 195F as is called for. I also put a new radiator cap on. I have been driving it all week now, and what I am seeing now is after 2 or so miles, the temp gauge will register 265F for 10-15 seconds, and then will quickly drop down 210ish (where it always ran prior to these issues) over the next 30 or seconds of operation. This can occur whether at a stop light or driving down the hiway. Again, never has it boiled over, no change in coolant level, no leaks etc.
So I am curious if my gauge or sensor is FUBAR, or if something worse is going on. I have purchased a mechanical gauge to put in it to see what the temp actually is running. I wanted to see if anyone has any ideas/suggestions, and I also wanted to verify that the dash temp gauge is the one that is in the side of the block and NOT the one on top of the motor near the thermostat. Right? I obviously don't want to do the work twice, and I know if I pull the computer's temp sensor my truck will run like a dog.
Big Chris