97 F -150 4.6L will not heat up. A little history. I bought the truck from auction a couple months ago. Not knowing what was done with the truck previously, I wanted to change out the antifreeze before it started getting cold here. I only drained the radiator and not the block and the old antifreeze didn't look too bad.

Everything seemed ok until the cold set in. The engine was taking a long time to warm up. After about a 10 minute warm up, I could turn on the heat and get warm air for maybe 5 seconds, then it would cool. This lead me to swap out the thermostat.

After I swapped out the thermostat, same problem. I hooked up an OBD2 scan tool and saw that even after 20 minutes of running, the coolant temp was still around 175 deg. During that time, it dawned on me that the radiator fan had been running for almost the entire time.

Any thoughts on what I should look at or how to troubleshoot further?

 

Pull the thermostat and make sure it's not stuck open and use a pot of hot water and a thermometer to check the opening temp.

 

sounds to me like you might have some air in your system, Take the radiator cap off parked on an incline with the front as high as you can get it. Run the engine keeping the reservoir at the full mark..

 

Replace the thermostatic fan clutch and verify proper thermostat operation and that its a 195. If the fan is constantly pulling air and won't disengage it's bad.

 

Thanks for the responses. Took all advice, removed new thermostat and verified it worked, pulled the truck onto ramps and ran it to get rid of any possible air, then today I swapped out the fan clutch...and it's still running and pulling air. After I changed out the fan clutch, I took it for a 20 minute ride on the highway, and the coolant temp still never got above 185 degrees, and it is a warmer day today. Fan clutch recommendation made perfect sense, now I'm stumped.

 

What is the problem you are still having? If the fan is running and the water not circulating, as the thermostat is supposed to regulate, the engine will still warm up. With a 195 degree thermostat, the coolant temp may only show 175 or 185 degrees, the heater should work with that.

I assume the heater not working is the problem you are still having. If so you will need to look into the heater aspect of things.

 

So with that temp, I should still be able to get heat? Right now, after a while of warming up, I can get about 5-10 seconds worth of heat, then it cools down. I can also change between heat and cold, so I'm assuming the blend door is working? Should I try to flush the heater core? Both the supply and return hoses feel hot.

 

Yes, you should have heat with a 175 degree or more engine coolant temperature. Changing the heater core on those is very time consuming, have to remove the dash I understand. I don't put much faith in that both heater hoses are hot scenario.

Backflushing the heater core would be a good place to start. Act gently because as mentioned those things are a beast to change. Good luck.

 

Flushed out the heater core and the heat seems to be good for now. Thanks again for the responses. Definitely seemed to be a little clogged. Put the water to the supply side first and a little stream with green coolant came out. Switched to the return side and a large stream with brown nasty coolant came out. Back to the supply side and the stream was much better. Back and forth for a few minutes and both sides had a good clear flow.

Maybe once the weather warms up I can see the coolant temps rise a little.

 

The thermostat is a 195 degree, right?
At about 175 +/- or lower a code will set for excessive warm up time.
A Scanner check should show between 190 and 205 as the thermostat, fan and outside temperature dictate.
Good luck.

 

Yes, thermostat is set for 195. Scanner shows max of 185 after 20 minutes of driving. I'm just happy to have my heat working now. Got some other issues to look at next.

 

Your thermostat is defective.

 

If the cylinder head temp sensor is detecting a 185 it will run the fuel richer and be cause for a loss of fuel mileage but the feeling of engine torque might be just a little greater.
Good luck.