I have a '93 F150 I bought new. It always had fantastic heat. Last winter I started having poor heat. I have done the following, all to no avail.

Changed Thermostat (several time, several brands)
Flushed cooling system and block
Verified computer temperature vs. actual water temp. OK.
Replaced Heater Core
Replaced Water Pump

Still, the heat is poor. It seems to have normal (very hot) heat when engine is at higher RPM (say highway speeds of 65mph or more). But at low RPM, around town, idle the heat is mediocre.

I have a remote start that I've used for years. My cab was ALWAYS toasty when I left for work in the morning. Not any more.

My feet are COLD! Any ideas out there?

 

You left one thing out. Have you checked the heater control valve? It is possible that it is stuck partially closed and when you throttle it up, it is forcing enough coolant past it to heat up the core. You covered pretty much everything else that it could be.

 

there is no water control valve on this year F150, only the door inside the heater box - which I have also checked.

but thanks anyway.

 

Check that the heater hoses are not reversed. It seems that it should not make a difference, but it does.
Bob

 

hmmm. good point. I don't recall if they are different size hoses, I don't think so.

So if they are the same size hose, how do I know which one goes where?

 

I believe the one from the engine goes to the tube closest to the engine, and the one from the water pump goes to the one closest to the fender. Or just switch 'em and see what happens.
Bob

 

I'll give it try. won't take long to find out, it was -20 this morning

thanks