Advance Auto Parts OBDII scan showed a possible thermostat issue since there is no coolant leaking. I am running the original Thermostat (18 years old, 384,000 miles. I'll be replacing the thermostat tomorrow.

 

No thermostat can be expected to go 18 years without problems. Impressive yours made it this far. Let us know if this clears the code/solves the problem.

 

It would help if you posted the explicit fault code instead of an interpretation that's ambiguous (and probably wrong).

 

SOLVED: First time replacement of thermostat and O ring. I am pleased with the mileage I got out of it. 18 years of service and almost 400,000 miles. Several coolant flushes along the way, too. I might just replace the Coolant Sensor while I'm at it at some point.

 

Is that the light that is just under the temp gauge? The small round yellow one. I have a 1999 Lincoln Navigator that has that light on.

Thanks,Dan

 

Dan, The light was the Service Engine Soon light (SES) that was glowing on the left side of the instrument cluster. I had someone attach an OBDII scanner to determine a code and it came up "Insufficient Coolant". I suspected the original Thermostat to the culprit since I had already flushed and filled the system with new coolant the previous year. Also, I was not getting any hot air out of the vents. I replaced the thermostat and gasket myself and it fixed the issue of SES light and no heat.
I am still amazed that the thermostat lasted as long as it did.

 

Thanks for the reply. I can not find anything on that light anywhere. Thought that might be it.

 

Refer to your owner's manual so that you can correctly identify the light that is on. The manual fully describes all of the lights by name and function.

 

I have looked through the owners manual several times and can not find anything about this light.

 

Post a photo of it. It may not be original.

 

I think it is fixed. I added coolant to the over flow tank. The next morning the light was gone. Would have liked to gotten a pic though.