My 98 F-150 4.2L engines temperature fluctuates from normal, all the way up to HOT, to the point the oil light comes on, then it will stay there for about 10 seconds then rapidly drop down to normal again. Also, the heater does not kick out any warm air whatsoever. My guess is that the thermostat is screwed?

If so what is the procedure to change it. I have only changed thermos on older trucks (1980 and older) and I don't suppose it is the same. What do I need to do? Any help would be greatly appreciated!

 

Drain coolant from the radiator until the coolant level is below thermostat housing. Take upper radiator hose from thermostat housing. Remove the bolts and lift cover off remove the o-ring seal. Use scraper get old gasket off. Make sure new thermostat the spring end towards engine. Apply thin coat of rtv sealent to both sides of the new gasket. The rest the same as removing just the opposite order. Hope this helps good luck.

 

As mentioned above, it is a fairly straightforward process.
I'd suggest buying a Haynes manual. It has lots of good info and pics to help guide you thru this and other DIY projects.

 

The only thing that bothers me, is that you said there is no heat coming out. That usually means that there is no water, or very little water in the system, or a major blockage. If there was water, and it was that hot,you would have mega heat. Take the chance to flush your radiator out as well. Just my .02

 

I am going to replace the thermostat first, then see if it fixs the problem. Thanks for your help guys.

 

make sure to bleed the air out.

 

how do you bleed the air out?? of the upper radiator hose? (i'm assuming thats what you mean)

 

The only reason I even mentioned it, is that I believe our trucks take the water from the engine without the thermostat in the loop for the heater core. I may be remembeing wrong, it old timer's kicking in.