i recently installed a new heater core in my 1997 ford f150 new heater hoses
also
flushed radiator coolant was very rusty and nasty
ran for 45 mins with cap off and heat on high
well the heater works fine if your at 3k plus rpms idling or in drive
once below that it blows cold air
so i installed a new thermostat thinking that might be stuck open or something
no better than before

will blow hot if driving hard
has 153k miles btw
the coolant will not boil over unless revved up with cap off
even after 50 miles of driving
is it the water pump?

please help thanks

 

by the sounds of the lack of maintanence on the cooling system it is likely your water pump. You need to change out your coolant every 100k because from the heating and cooling it becomes very acidic and will eat away at the impellers on the water pump. It is likely your water pump doesn't have enough of the impellers left in order to push the warm coolant up through the heater core unless revved above 3000rpm

 

well i have an update it blew the passenger side heater hose off going down the interstate ok so i put it back on and kept going
are they designed to let go with pressure i have been driving it for like 300 miles
since i put it on

 

havr you checked your level recently since if you are low it will not get coolant to your HC.

 

Ya might have to "burp" the system. Sometimes ya can get air in the system when doing all that stuff. Makes for a not so good of a working system.

 

I, as well, am having this very issue with my 4.6L. Is there any way to easily look at the impellers? Or is there a way to see the coolant moving around?

 

x2 mine was blowing warm air and checked the coolant level. nothing in the reservoir. added about 45 oz. of water and i had my heater back

 

i have plenty of coolant .alright now mine is doing something different since new heater core water pump and thermostat.
when i first drive it in the morning the temp gauge goes up about a third of the way. warm heat then it drops all the way to cold.

if i stop the top rad hose is about to bust ,so i let the pressure go slowly from the cap on the expansion tank .it bubbles up a few second the temp goes back up and the heat blows hot .i have to do that about three times every morning after that its fine til the next time i drive it.... any body?!?!!?

 

oh my water pump propellers were completely gone none left
it was paper thin the new one is nice and beefy 1/8 inch blades...
still acting funny

 

Did you get the right temp tstat?

 

i got 195 and checked it

 

agree with ram-air,sounds like you need to burp air from cooling system.

 

how many miles/ hours should it take to burp the system goodness seems like i have driven 20 thousand miles well probably more like 200 still acting funny with air in it

 

Hi everyone, my problems are the same, no heat, one side of the h/c hose hot, the other cool. new t-stat installed correctly, system flushed and good flow though the h/c. Now suspecting the water pump, any other ideas before i spend time/money on the pump?...help! it's cold out here

Thanks
Satman

 

I had this same problem, changed everything except water pump, nothing worked. Took water pump off, and there were no impellers left to circulate the water, changed with a new one and everything is nice and toasty, would consider trying this!!