Heat Not Blowing Hot, Upper Rad Hose Hot, Lower Rad Hose Cold

[SAC81]

So my GT is put away for the winter...I keep it at my grandparents house, parked in their driveway.

When I visit them on Sundays, I start the car up and let it warm up.

Today, started the car and went in the house. Five minutes later I came back out. I noticed that it was past halfway on the temperature gauge, so I threw the defroster on maximum heat/maximum fan- it was cold. The air was not even warm.

So I popped the hood...I was assuming I had a stuck thermostat...

The upper radiator hose was hot.

The lower radiator hose was not warm.

WTF?

Doesn't a warm upper radiator hose indicate that the thermostat is working? How is it even possible that the upper hose was hot and the lower hose was cool?

I didn't have time to look the car today and probably won't until next week...now that I'm home though, thinking about it is driving me crazy. WTF could the problem be? Some sort of block in the cooling system?

[George C]

stat is sticking and not allowing coolant to pass through

[Domination]

Dont matter if stat is opperational, or even there. The heater core is on the engine block side. If stat sticks closed then the heater core still sees flow. What your going to need to look for is reasons that it is either not getting hot, or air is not being directed over your hot heater core. Rarely have I seen malfunctions with the heater box itself. First thing check your fluid level. The temp guage doesn't show how hot your rad is. Just coolent in the block. Don't worry if your stat only open just a bit and closed when it let really cold water in from the rad and didn't get the rad heated up all the way. Grab the hoses to and from your heater core. See if both of them are hot.

[somethingclever]

COuld be the mechanism that operates the door to the heater core. Fairly common problem.

[SAC81]

Thanks for all the feedback...


Dont matter if stat is opperational, or even there. The heater core is on the engine block side. If stat sticks closed then the heater core still sees flow.

Exactly, that's why I figured it wasn't the thermostat.


Grab the hoses to and from your heater core. See if both of them are hot.

I forgot to mention that I did (I guess that was kind of important), neither of them felt warm.


First thing check your fluid level.

Fluid level was good.

What really sticks in my mind was that the lower radiator hose was cold, while the upper radiator hose was hot.

[Stangman701]

I would sometimes have trouble with my 85 GT at the beginning of winter. I guess it was just the heater core being a little clogged. If you unhook the two hoses that go to the heater core and flush them in both directions with a garden hose you should hopefully fix the problem, that would always work for me :goodidea:

[Domination]

If neither hose to or from the heater core is warm when the guage says the engine is up to temp there is a flow blockage. Make sure there isn't a valve that is suposed to open to the heater core when the heat is turned on. Normaly it will be vacum operated if you have one. It will make a damn mess if you deside to flush your heater core with a garden hose. Its pretty easy to see if you system is starting to gunk up though. That shit doesn't only accumulate in the heater core. Under the rad cap will have all kinds of gook, as well as in the overflow bottle.

[George C]

my notch was like that and the head gasket was the culprit, took a while for it to finally show its ugly face and now its fixed its fine

[lib88stang]

My Dad had a air pocket in his cooling system in his notch, he burped the bleeder on the thermo stat housing and it fixed his problem.

[SAC81]

Thanks all. I don't believe the system would be "gunked"- I flush it once a year, and the fluid in the radiator looked good.

I'll be looking at the car again tommorow and will report my findings. At this point, I'm thinking either:

1. My antifreeze/water mix was poor and a small chunk of ice formed, causing a blockage.

2. It's a big airpocket somewhere.

I'll probably try burping the system good tommorow and see what happens.

If I don't get a resolution I'll be real stumped.

Thanks again.