I have a 1994 Ford F150, 5.0 with A/C. A little while ago I noticed that I wasn't getting enough heat, I went and checked the coolant level and found it was ok. I checked the upper hose and it was warm and then checked the lower hose and it was cold. So I installed a new thermostat and CTS. Still I get the same problem. I rechecked the upper hose and it gets hotter. I had installed a new radatior last year.

I slid nearly off the upper hose to see it the thing was air bound and had no air come out(engine running) had some pressure, but was afraid to remove it off completly. I then pulled off the return heater hose and had flow come through. At this time I saw that the flow was very little. I checked the heater controls and found them to be working ok (flow door). I have no leaks or strange noises.

Questions
1. Could this be a problem with the water pump. Has anyone ever had a water pump go bad without leaking or making a lot of noise.
2. Could the heater core be plugged up (seems to me that there would be more pressure even if it were clogged up). Flow seems to be 1/5th it should be.
3. Would the bottom hose stay cold even after running the engine up to operating temperature.

Thank you in advance
Droff

 

If the engine doesn't run hot, the pump is probably ok.

I have had partially clogged cores before. I hooked a garden hose to them and blew them out in reverse flow with excellent results. Just beware if the core is weak, 40~80 psi of water pressure will blow a hole in it. When I did it I figured I was buying a new core anyways.

Another thing to look at is I have had foriegn objects get lodged in the air door and not allow them to close all the way. But with you having A/C, since your interior will be exterior when you get to the air door you may as well replace the core.

If it were me, I would attach a hose, and slowly open the faucet while watching flow, and watch all the gunk come out.

Good luck!

 

You might want to check the lines to the heater core to see that they are both hot. It sounds like you might have a blocked heater core. They are around 50 bucks and don't take mauch to replace.

 

is it possible that the valve that allows coolant to flow into the heater core is not functioning properly

 

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there is a vacuum line coming of the valve on the heater core hoses take it and hook the line up to straight manifold vacuum if you then have heat it is the control board inside

 

I think you have a partially clogged heater core. I had that happen on a vehicle once. I had no heat in a blizzard. I fixed it the next day.