I live in Kansas, and the temperature here for the last couple of weeks has been in the low teens with highs in the 20's, if not colder. Starting this last week, when I am driving down the road, everything seems fine. When I get to a stoplight, if I have the heater on full heat, the temperature of the air coming out drops down to near outside temperature, until I start to go again, in which the temperature of the air comes back to normal. I thought it was just the temperature of the outside air, until today, when I was on the highway. Going along down the highway, every now and then, the temperature guage will go up very high, nearly touching the red, and the air coming out of the vents gets very cold. Then all of a sudden the temp guage drops back down to normal, and the air gets hot again. The first thing that came to mind was the thermostat, which I tried to replace tonight but found out by experience the difficulty of changing the thermostat on the 4.2. If anybody has any ideas, I would appreciate it...thanks.

 

all i can think of is a thermostat that smokes crack....

maybe a belt/pulley issue, but that's doubtfull

good luck and let us know what happens

 

Sounds like you have a circulation problem. Either caused by the thermostat, or a clogged or faulty radiator. I have an '02, and I had to replace my radiator last spring. I replaced everything else (pump,thermostat,etc..) to the tune of about $400 total ,before I replaced the radiator. I even had the radiator flushed 3 times, but it didn't help. The thread is still around somewhere. I believe Brian A. started it, something about "running hotter than normal" , check it out.

 

Low coolant would be the most common cause. Just those symptoms.

 

I didn't suggest that 'cause I thought it would be too obvious, but a very good idea.