My '92 F150 (168,000 miles) has been partially retired for about a
year. I use it to take the garbage down the driveway, and haul things
here and there. About 2000 miles a year.
I just noticed that the heater was blowing lukewarm air. The
temperature gauge was on the high end of normal. Then, the gauge went
down to the low end of normal rather rapidly, and the heater was
blowing regular, warm air. It then went back up and blew the lukewarm
air. This cycle repeated about every few minutes.
I fully suspect this is a bad thermostat, correct?