Hey guys! I'm new here but certainly not new to Fords...love em!

Ok so i just bought this 97 f150 flareside 4x4 and have been fixing all of her "little issues" one at a time.

I'm not getting heat and winter is approaching! Truck runs fine...already did a coolant flush and check thermostat in boiling water, it works. Temp gauge always warms up to 1/3 of the gauge and stays there.

Heater blower blows and blend door is fine.

Pulled the heater hoses with engine running and pressue/flow was weak. Hooked it all back up and decided to really rev her up. All of a sudden I had heat and it stayed hot. Then I let her cool for hours and took it back out at night. This time I drove her normal and didnt rev up the motor. Still had great heat!

Next day...started her up...NO heat. Revved her up...warm for a second...then went cool again. Didnt work like the first time.

I'm thinking water pump...? or something with tensioner?

Any testimonies, thoughts or ideas would be much appreciated! Glad to be apart of the Ford Truck Family! You'll come to find I'm a team player

Ryan

 

Change the thermostat I put them in boiling water test to that doesn't mean its working all the time also their is a mark on the belt tensioner that tells you when your belt is stretched I also have seen them have air pockets in the hoses to the heater core that have caused them to do that good luck and let me know what you find

 

Sounds like you have a partially plugged heater core. done a few of these and they involve some time. you need to pull the dash out to replace it. before you do though you can try to pull the hoses off of the heater core and attach short pieces that you can use to direct some CLR through it from both ways until it flows clean. the problem is that that heater core is a radiator style core so the coolant does not only have one path. so what happens is that most of the core is plugged with corrosion and lime and the coolant is only passing through a section of it which is not enough to get it hot. (by the way this assumes you have bleed the system properly and do not just have an air pocket, in which case you just need to pull the cap off and let it run with the heat on until it burps out) hope this helps.

 

I'll try to find that mark you were talking about to see if my belt is within specs...I dont think its air in the system or the thermostat though because Ive had the heater hose off and the problem was I wasnt getting much coolant pressure flowing into the heater core. The upper radiator hose is hot and stiff once the thermostat opens and the gauge reads normal and truck runs great. If it was getting stuck shut it would overheat and if it stuck open it wouldnt warm up.

Wonder if anyones had the water pump strip or break blades or the tensioner thingy stock working? That would cause low pressure right?

 

Never heard of a water pump doing that you would probably know if the tensioner was bad you belt would slip

 

Hmmm

 

Ok so check this out. I was talking to my buddy and his friend had a 99 expedition lose heat but ran totally fine and he pulled the waterpump to find that all but 1 fin was missing. So basically that 1 fin was enough to flow coolant to keep it running fine but not enough to push coolant up and through the heater core with any force. So when it was revved up to high rpms that 1 fin acted like 3 or 4 fins with the flow it was producing thus producing adequate flow and heat.

Anyone else buy that but me? lol

 

Pull it off and see but I've never heard of that that's you call let us know if that's it

 

The only times I had your problem with a vehicle it was a bad thermostat.
This is why the boiling water test fails. If the thermostat opens too soon or is weak, it never allows the engine to heat up properly so when you stuck it in boiling water, you might have put it in water a lot hotter than your engine gets so it fooled you into thinking it was not defective.
They are cheap and you know how to replace it, so I would replace it and see before getting into other things.
Based on the temp guage, it sure sounds like the thermostat is lazy.
My experience has been it is almost always the obvious and the simple things with car repairs and replacing parts. I learned my lesson the hard and expensive way.

 

Yes replace the thermostat first before you take the water pump off