Thermostat Or Water Pump Or...?

[BDD]

I have installed a new thermostat in my 1972 GT. Spring side down in the housing. The temp. gauge goes to the middle of the scale and above so I shut the engine down to avoid overheating.

At what point on the gauge should the thermostat open? I assumed that it would open before the temp. climbed much above the middle of the scale.
As the temp. climbed the last time I started the engine it suddenly popped down to the middle of the scale but rose again so I shut it down again.
I thought that this might have been from the thermostat opening but probably not because the engine was hot and the radiator was cold. The top radiator hose was cold too. With the radiator cap aff I saw no movement in the anti-freeze that's visible there.

Does this mean, by definition, that my water pump is not working or could something else be causing this?

I don't see how that thermostat could be getting hung up in the housing. I kept the old thermostat gasket but since it's not leaking I don't see what other problems an old gasket could cause.

[namba209 (R.I.P.)]

Did you check the thermostat before installing it? I've seen new ones not work. To check them, put it in a pot of cold water, on a stove, turn on the heat, and check the thermostat for opening at the rated temp. This can be checked with a cooking thermometer. The cylindrical part of the thermostat should be installed in the housing so that it in the block side of the cooling system. HTH.

[BDD]

Namba:

I didn't check it because it is brand new. Now, It's kind of difficult because it's been in the anti-freeze, etc.

I don't hear any squeaking or noises from the area of the watre pump. It does not appear to be leaking.

[Lindsay]

Hopeful you installed 180 degree thermonstat and not 195 degree.

GT Temp Gauge Indicator:
http://www.opelgt.com/forums/attachm...agemarkswc.jpg

[BDD]

What I did was go to Autozone (they had one in stock) and asked for the right thermostat or my car, year, model, etc. When I take it apart I'll check that. My old one has the temp. stamped on the top.

I guess I could put it in a coffee can on the grille. That would avoid poisoning anybody. Don't know what I'd use for a thermometer though.

[jeff denton]

Was there a problem before you changed the thermostat?
Did the new thermostat have a little bleed hole in, if not, did you drill one?
Also I'm wondering if there's some air in the system somewhere, maybe it needs a good burping.

[Lindsay]

What I did was go to Autozone (they had one in stock) and asked for the right thermostat or my car, year, model, etc. When I take it apart I'll check that. My old one has the temp. stamped on the top.

I guess I could put it in a coffee can on the grille. That would avoid poisoning anybody. Don't know what I'd use for a thermometer though.

I use a meat thermometer with metal stem/ probe.
Look for one in the gadget aisle of grocery or discount store.

[BDD]

The temperature was getting high before so tried a new thermostat.
Is the bleed hole in the disc of the thermostat that sits on the thermostat housing?

What are the signs to look for to identify or rule out the water pump as the problem?

[tomking]

Your water pump is not the likely cause of the car getting hot, if it is getting hot. I am assuming you are not constantly finding the car low on coolant. If you are then the pump is the likely cause. But assuming you are not losing coolant, then the pump is not the place to start looking. The thermostat is one place but the other is the radiator. Have you flushed the coolant system? If the radiator is not a new one and you have not flushed the system then that is a thing to do. Is the radiator dirty with bugs etc? Clean it off. Do you have a fan shroud? If not then buy and install one. From what you have stated I am not sure your car is getting hot, but you may be assuming it is going to get hot because the gauge reads at high normal. Maybe it isnt getting hot, but just a faulty or high reading gauge?? Let it warm up and idle with the rad cap off. That way you can see when the thermostat opens and you can monitor the gauge reading. But before you do that follow the advice already given and make sure your new thermostat works. You can drill the small vent hole in the thermo plate if it doesnt have one; this allows any trapped air to vent and allows a tiny bit of water to bypass in case the thermo doesnt open. Search this site for thermostat and cooling issues and your answer will probably be found. Good Opeling.

[broszzy]

Run it with no thermostat and check for circulation. you should check the radiator fins for dirt, and junk, or bent fins that will block air flow. When was the last cooling system flush?

Broszzy

[free4u2nv]

put it on the stove in a pot. I drain antifreeze in the pots out of my kitchen and I'm still kickin'! aluminum pot if you have it. If you have a wife....wait till she goes shopping....or you may have 2 overheated problems!!!

[Dennis Texas]

Do you really have an overheating problem? Does the temperature really get that hot? Your instrumentation is about 35 years old or so you may want to run engine and check the actual water temp and see how it corresponds to the gage, If thats not suspect then like mentioned above may need to have some radiator work to be done.

[timemachine]

As I think someone else mentioned, I've had this happen just because there was an air pocket above the thermostat. Give a squeeze to the upper hose to be sure it's got coolant in it.

Jim

[newman27]

I have installed a new thermostat in my 1972 GT. Spring side down in the housing. The temp. gauge goes to the middle of the scale and above so I shut the engine down to avoid overheating...

As others have stated, I'm not sure you have a problem. My cooling system is in good working order and my temp gauge (after the car is fully heated up) runs at the midpoint of the scale while moving and will occasionally creep toward the 3/4 mark while standing at a light.

...Let it warm up and idle with the rad cap off. That way you can see when the thermostat opens and you can monitor the gauge reading...

This is interesting. How will you know when the thermostat opens - by a change in fluid level? Can this method be used to calibrate the temp gauge in some way using a thermometer?

[deaner]

The temperature was getting high before so tried a new thermostat.
Is the bleed hole in the disc of the thermostat that sits on the thermostat housing?

What are the signs to look for to identify or rule out the water pump as the problem?

I would suspect the radiator. You didn't say what kind of condition it's in. You can and should back flush the radiator. Make sure it's flowing enough coolant. Also check for air bubbles, (as in making sure the head gasket is not leaking).

[namba209 (R.I.P.)]

This is interesting. How will you know when the thermostat opens - by a change in fluid level? Can this method be used to calibrate the temp gauge in some way using a thermometer?

Two ways to know when the thermostat opens, the upper hose gets warm/hot, cancel the second on a GT, the radiator cap is not above the upper tank. But if it was, you could see the coolant flow across the top of the radiator below the hole. You could use a cooking thermometer in the cap hole, but because it's out of the mainstream of flow in will only be in the ballpark. Check the link in post #4 of this thread, Lindsay put in a link that show the temp versus the bars on the gage in F and C.

[BDD]

When I test ran the engine for a while the other day after replacing the booster vacuum hose, the voltage regulator and having put new electrodes on the Bosch coil (getting ready to go to an electronic ignition) the temp. gauge showed a very high temp. I was distracted checking other things but noticed that it was near the red. So I shut it down. That's what prompted me to try a new thermostat. It had gotten warm before so this isn't a new issue. Now that it runs better I'll be running it longer so need to keep it cool.

From the outside the radiator seems to be in excellent shape. The fins are straight, no bugs, no leaves...it just looks a little dusty on the front side. The shroud is bolted on and hasn't been chewed up be the fan. The plastic fan blades seem to be in good shape too.

I see no signs that there are any leaks at the head gasket.

The first time it got hot I think that the top radiator hose was hot too.

So I put in a new thermostat. The top hose was practically dry at that point. I could not see anti-freeze in the radiator so after changing thermostats I put some premixed antifreeze in. It didn't take much at all to bring the fluid level to where I could see it.

The next two times I ran it the radiator and hose didn't seem to get hot but the engine did.

I just called the store where I bought the thermostat and they said it was for my car and it opens at 195 degrees. I just returned it and got one that opens at 160 degrees (too low or o.k.?). I'm only going to drive the car in Spring, Summer, and Fall. This one is a Duralast and it does have a small hole in the top, wide disc with a small metal stopper that looks like it's intended to allow flow from radiator to engine but might restrict it going the other way.

The last time I ran the car I squeezed the top radiator hose and there was some coolant in it but it didn't seem like much.

When I took my thermostat out to return it a few minutes ago the coolant on the engine side was under just a bit of pressure (totally cool, hadn't been run in a day) so some flowed out. On the radiator side the hose was wet but no coolant to speak of.

I won't put this thermostat in until later.

[BDD]

I just went out and started the engine with no thermostat. I started with the radiator cap off. Shortly, I could see the coolant moving around with air bubbles in it. It was kind of frothy. I figured, if nothing else, the water pump is probably moving things around. So I put the cap on. I suppose the air just floats to the top hose when it cools down and isn't pressurized.

Ran the engine for several minutes. It stayed cool (temp. gauge) and maybe got 1/4 of the way up. Never got up half way or hotter.

Shut the engine down and now the radiator was hot and the valve cover was just warm. The top radiator hose was hot now and could hear collant sloshing around.

Not having the thermostat in made a huge difference. I guess it's a matter of a thermostat that works and getting any air bubbles out.

[trlmr]

Have you driven the car enough to see if it is using coolant? If it doesn't quit making bubbles and froth in a short time it may be something other than a thermostat

[jeff denton]

What is the heater core doing all this time when you're testing? You want the heater turned on, in other words coolant flowing through. Otherwise it might just contain a big air bubble.
Somebody wondered how hot is what you call "hot", and how trusty the gauge is. Good point. How hot is it, what is the temperature in degrees? (I love my infrared thermometer when trying to figure things like this out! It's really neat to be able to check out temp diffs all over the engine.)
A constant stream of bubbles venting out the top of the radiator is not a good thing.