Heat Not Hot, Upper Radiator Hose Hot, WTF

Swarzkopf · Nov 12, 2006

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?

Feedback is appreciated as always.

parchisi · Nov 13, 2006

Maybe somethings up with your heater core. I don't think they're too expensive to replace.

HISSIN50 · Nov 13, 2006

How did the heater lines feel?

How cold is it at your grandparents' house? Your radiator is rejecting heat really, really well.

Good luck.

Adam95GT · Nov 13, 2006

yea check the heater core... you also need to let it run for a decent amount of time for the thermostat to open...

Swarzkopf · Nov 13, 2006

It's 180* thermostat. I'm sure that after running for 10 minutes, showing over halfway on the temp gauge, and having an upper radiator hose HOT that the thermostat would open, regardless I don't believe that that was the problem due to the situation I described where the upper radiator hose was hot, but the lower was cool.

I don't think it's a heater core problem- again, the sticking point to me is that the upper radiator hose was hot, the coolant in the block was hot (as evidenced by the temp gauge), but the lower radiator hose was cold.

How did the heater lines feel?

Both cold.

How cold is it at your grandparents' house?

About 35* F.

Basically, can anyone explain what could cause the upper radiator hose to be hot while the lower radiator hose stays cold?

Thanks guys.

1TallMF · Nov 13, 2006

I'm more or less stumped...

All that comes to mind is perhapse a blockage in the radiator causing the coolant to not really flow anywhere. Or, the water pump isn't, err, pumping for some odd reason

Methodical · Nov 13, 2006

When you run the car again and let it come to normal operating temperature, shut it down and then feel the radiator for cold spots. I had an 80 Supra and had the exact same problem and the radiator was cold in the center. I removed the radiator took it to a shop and the guy rodded out the radiator - basically all of the center cores were blocked. Of course, you would just have to replace the one in your car because I don't think you can open it up. Peace

Adam95GT · Nov 13, 2006

take it for a drive... i still dont think the t stat oppened...

Swarzkopf · Nov 13, 2006

When you run the car again and let it come to normal operating temperature, shut it down and then feel the radiator for cold spots. I had an 80 Supra and had the exact same problem and the radiator was cold in the center. I removed the radiator took it to a shop and the guy rodded out the radiator - basically all of the center cores were blocked. Of course, you would just have to replace the one in your car because I don't think you can open it up. Peace

This is what I'm afraid of...

My radiator is pretty new, just put it in last year.

take it for a drive... i still dont think the t stat oppened...

Coolant flows in this direction: from the bottom of the block, through the lower radiator hose, through the radiator, through the upper radiator hose, through the lower intake manifold, into the block, and back to the lower radiator hose.

A stuck thermostat will result in the lower radiator hose heating up as hot coolant from the engine trys to flow into the radiator, while the upper hose remains cool because the coolant in it is not heated and not flowing because the thermostat is closed.

Hence, a stuck thermostat is not the issue here as my situation is the exact opposite- I was hoping someone had a suggestion as to a common problem. Obviously, there is an obstruction somewhere between the lower intake manifold and the radiator blocking coolant flow. The thermostat is opening, and allowing warm coolant to mix with the coolant in the upper hose, hence the upper hose being hot.

If anyone has any other clues as to what the blockage could be, fire away.

1TallMF · Nov 13, 2006

Swarzkopf said:
Coolant flows in this direction: from the bottom of the block, through the lower radiator hose, through the radiator, through the upper radiator hose, through the lower intake manifold, into the block, and back to the lower radiator hose.

Um, I'm about 99% sure its the other way around. Your thermostat opens when the coolant reaches a certain temperature, allowing it to flow to the radiator where it can be cooled. Your thermostat is working since hot coolant is getting at your upper rad hose, but it is not flowing down the rad like it should. Since there is no good flow out the thermostat, the hot fluid also can't make it to the heater inlet hose. Can a third party confirm either case? Maybe I'm on crack in my reasoning...

Adam95GT · Nov 13, 2006

i though it said it was "hot" not hot coolant... in the upper hose that is... i know the t- stat has to alow it to pass in to the upper hose... Did it have coolantin it?

LoudToy958 · Nov 14, 2006

Two things pop into my mind - one is there is an air bubble that worked its way around the system and is holding things up, unlikely it would show this far after a coolant change, but possible.

Next, test your coolant, and see if its good. Maybe your mix is more water than you think. With the temps you guys are getting over there, it could have a chunk of ice in it somewhere. That would account for the upper being hot, and the lower staying cold.

Good luck, worst case, I would say your rad is toast. Could be worse.

Keep us posted, curious to see this one solved.

'94ChickStang · Feb 7, 2007

1TallMF said:
I'm more or less stumped...

All that comes to mind is perhapse a blockage in the radiator causing the coolant to not really flow anywhere. Or, the water pump isn't, err, pumping for some odd reason

you're radiator is blocked, it doesn't matter if it's new or not. If it wasn't flushed properly when changed it could get deposits right back in the core

1TallMF · Feb 7, 2007

Holy random thread resurection, batman

sl03gt · Feb 7, 2007

Wrong coolant mixture, your radiator is frozen. Seen this on a few cars this last weekend were the engine would warm but there was no heat. Eventualy the car would over heat. First see after warming if the lower radiator is hot. If not your radiator is frozen. Hope this helps.

1TallMF · Feb 7, 2007

That would make alot of sense. But was it really that cold in Pittsburg in November when this thread was started? I know it was still well above freezing up here in the great white north.

sl03gt · Feb 7, 2007

Didn't look at the date. Oh well. Hope he got it fixed.

Heat Not Hot, Upper Radiator Hose Hot, WTF

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