Truck doesn't heat up!
 

I have a '92 f-150 with the I6. For some reason it won't get up to temperature. Last week i drove about 150 miles without stopping. The temp gauge never even got up to normal range. The gauge moves up and down the way it should depending on what type of driving i am doing but it stays in the "cold" range. I thought the thermostat was stuck open so i replaced it 2 days ago and nothing changed. After about 4 miles of city driving i have do have sufficient heat so could it be just a faulty gauge?

-Jon

The temperature sending unit would also be a suspect. I kind-of doubt that it's the gauge, typically you don't get a bad gauge. Kenster is correct in his thinking. If you are getting heat then you engine is getting warm you just have a problem getting the signal to your gauge check the sending unit and the wires going from the sending unit to the gauge.
My .02.

Ok so to check the sending unit i would just use a multimeter to check the resistance across the unit and if it reads wide open then the unit is bad right?

-Jon

If you are getting warm air out of your heater, I would say the engine is heating up just fine and your guage is shot.

My old '90 with the I-6 did that right before I got rid of it. You could let the truck warm up for 15 min and the gauge would read warm. Drive it and it would go to cold. Thought the same thing you did too. Took it to where my Wife works and let their guys look at it. Bad upper rad hose. Check your hoses. Mine was wore out and doubleing in size when the truck heated up. New hose good to go.

------------------
'01SuperCrew (Gen1) 4.6L,Auto Trans Black,Lund Stainless Steel Grille and Bumper inserts,Westin Nerf Bars,Extang Black Max Tonneau Cover,Tinted Glass,Front and Back Door and Rear Window Vent Visors,Billet Third Brake Cover
'00 F150 Flareside Sport,4.2 L V-6,5-Speed White,Factory Steps, Tinted Glass, Billet Third Brake Cover http://albums.photopoint.com/j/Album...525&a=11310714

I had the same thing happen on my '92...one word...THERMOSTAT... that's the first thing I would replace, because 1, it's easy, and 2, dirt cheap. Odds are that will take care of your problem