Having a little problem with my 1984 F150 (V8 5.0L). I let it sit for about a week in the cold and when I started up again the temperature gauge never went above "Low". Fan also doesn't seem to be putting out as much heat as it normally does. Checked the coolant, topped it off, drove it around some more and the temp came up a little bit but nowhere near normal. Just trying to figure out where to start looking to diagnosis this. Do I just need a good coolant flush? Could it be the sensor? Any suggestion on where to start are greatly appreciated. Thanks!

coolant, temp gauge, low heat, low temp

 

Well how long was it running?

 

Mne always said it was on the low side of normal. I installed a mechanical gauge at it runs around 190*.

I have electric fans though so warm up is nice and quick.

 

As LaMartian ask "How long was it running?" and I will add How long did it take for the gauge to indicate an increase in the temp? (thinking the thermostat could be stuck open)

 

Thanks for the responses. I've run the truck a couple times in the past couple days. I usually let it warm up for about 10 minutes, but I've driven it for over 40 minutes at a time. It takes the initial 10 minutes for it to go from 'zero' to 'low', but never gets close to 'normal'. The heat is warm but not hot. Where is the thermostat located on this engine?
Thanks!

 

Follow the upper radiator hose to the top of the engine to where it connects, that is the thermostat housing. If you remove the housing don't forget to remove the old gasket and put on a new gasket when you put it back together.

Hope this helps

 

Thanks! Any thing else to look at replacing when I pull that off? (hoses?) I'm assuming flush the coolant too?

 

There isn't much else to look at in there except for maybe debris or hose condition. I'd definitely flush it since you're going to have it apart anyway. When you flush, remember to reinstall the hose without the thermostat and run the truck for a few minutes without the stat in so the water pump can flush through the system in a constant loop, then drain and reinstall the stat and fluid.

 

Does your heater blow hot air? Easiest way to tell if the truck is actually running cold or not.

Thermostat is your most likely candidate. Take it out and boil it in water on the stove to see if it opens and closes as it should. If you replace it, test the new one the same way before you put it in, they have a tendency to be DOA.

Sensor is unlikely because the gauge moves some. They are cheap and easy if you ever need to do one in the future though. A coolant flush won't fix this problem, but it may be a good time to complete one. If you decide that the coolant looks fine or you don't have time, you shouldn't lose much coolant just swapping the thermostat though.

 

Not sure how old the rest of the system is, but now might be a good time to do some preventative replacements.

If you are gonna replace the t-stat, replace the water pump and all of the belts too. The parts are cheap if you order online.

That's my $0.02.