Dancing Temperature Gauge

[bigguns]

When my 2002 Explorer XLS is stopped at a light my temperature gauge will rise. Then it will fall back to the middle without the car moving. Then maybe it will go up to notches. Then come back down. The gauge always stays in the middle when the car is moving. Also when the car is put into park the temperature gauge will stay in the middle.

I got an oil change a few days ago and the issue went away. Today it reappeared. I did ask the auto tech if my coolant was good and he said it was.

I have read online that the issue could a bad thermostat or that my radiator needs to be flushed.

Does anyone have any ideas where I should begin?

 

[gsmaclean]

Thermostat. No question.

 

[bigguns]

Today I replaced the thermostat and gasket. It stated to leak from the middle of the housing. It was not leaking before I replaced the thermostat. Any ideas what I could have done wrong?

Just took it apart think that the o-ring slipped off but it was in the correct position. Just leaking from the seam that touches between the top housing and the bottom housing.

After reading some more it seems I forgot to note which orientation the thermostat would go in. there a little hole with a piece of metal in it to let air out I assume and I don't know which way its supposed to be pointing.

 

[jrford]

Little hole is should be on top, its a vent so it needs to be at the highest point. Maybe a real thin coat of RTV round and under the rubber gasket, be careful not to use to much.
did you get a new o-ring? i don't have a pic or the Ex with me any chance you could post a pic?

 

[bigguns]

Followup.

Notice the old o ring was much thicker than the replacement I got from autozone. Went to Ford and got the official motorcraft thermostat and o-ring and it worked perfect. Filled up the coolant with some prestone 50/50 and the truck worked fine in 6 o clock traffic through downtown Orlando tonight.

All is well. Except for the Door Ajar light and the oil gauge that stays all the way down until the car heats up. :