Odd overheating problem

[gtblast]

I took my 70 GT project out for a long spin yesterday. I was gone about an hour, and I even took it up one of the small nearby mountains. It ran great! I came back home for a short pitt stop and then headed out again for a drive. This time, about 10 miles out, the engine temperature began to climb. So, I pulled in a gas station and popped the hood. The coolant overflow bottle was almost full, so I shut it off and let it cool down some. When I shut it off, it began to percolate and belch steam out of the overflow container. I let it cool and restarted it. The temperature had dropped some, and most of the coolant had been sucked back into the cooling system from the overflow container. I started my trip home, but the engine temperature never returned to where it normally runs, it stayed up higher than normal. When I got home, the engine temperature was still higher than normal, but the level of coolant in the overflow container was normal. When I shut it off, no percolating or belching of steam.

The normal running temperature is usually in the lower 1/4 to 1/3 of the gauge. However, when it decides to overheat, the gauge goes to about half or a little above.

This is the second or third time this has happened in the last few weeks. I take it out and run it for an hour and all is good. Next time I go out, I get 10 miles from home and the temperature ramps up.

The radiator was cleaned and tested by a radiator shop and was declared by them to be good. The radiator hoses are good. The thermostat is a 180 degree unit and I tested it myself in a pan of water on the stove and it is good. I am using a fan shroud and 5 blade fan, and running a 50/50 mixture. Stock engine with a Weber 32/36. Fan belt appears tight enough. Timing is on the money.

The only other clue may be in the speed of driving. The first trip out, I did not go over about 40 mph, but I did climb the mountain. The second trip out, was more 50-55 mph for a while. Perhaps the radiator can not handle the increased demand at higher speeds? Some things I can try are to run it without a thermostat and see if that helps. Also, I will pay more attention to the possible connection to speed. I flushed the system a couple of months ago, but plan to do it again. Any insight before I do would be greatly appreciated.
Fred

[baz]

pop a new sender unit in it may have gone bad !

grounds may be corroded and giving faulty readings !!

voltage regulator may be going bad !!

does it have a fan shroud if not it may not be pulling air through the rad good enough!!

gauge may be going bad !!

i may get bored and stop typing before the end of the list .

[opelnut10]

With it coming on all of a sudden I would look at changing the thermostat and make sure the hoses are not going bad. Most GT's need a seven blade fan and a shroud to move enough air through the radiator. I also run Water Wetter additive in my system which will drop the temp about 15-20 degrees. The temp sender will give false readings also if the system gets low on coolant and it is not fully submerged in the water neck. Just a few things to add to the other list to check out.

[ungermm]

It does sound like you have a problem with coolant circulation in which part of the system is hotter than the other. That might explain the percolation and belching. I would try running without the thermostat first. I've tried the stove top method to test thermostats. However, I wouldn't trust this test. So, maybe just replacing one is the best option since they are one of the least expensive and easiest things to replace.
Jerry

[tekenaar]

Originally Posted by gtblast I took my 70 GT project out for a long spin yesterday. I was gone about an hour, and I even took it up one of the small nearby mountains. It ran great! I came back home for a short pit stop and then headed out again for a drive. This time, about 10 miles out, the engine temperature began to climb. So, I pulled in a gas station and popped the hood. The coolant overflow bottle was almost full, so I shut it off and let it cool down some. When I shut it off, it began to percolate and belch steam out of the overflow container. I let it cool and restarted it. The temperature had dropped some, and most of the coolant had been sucked back into the cooling system from the overflow container. I started my trip home, but the engine temperature never returned to where it normally runs, it stayed up higher than normal. When I got home, the engine temperature was still higher than normal, but the level of coolant in the overflow container was normal. When I shut it off, no percolating or belching of steam. The normal running temperature is usually in the lower 1/4 to 1/3 of the gauge. However, when it decides to overheat, the gauge goes to about half or a little above. This is the second or third time this has happened in the last few weeks. I take it out and run it for an hour and all is good. Next time I go out, I get 10 miles from home and the temperature ramps up. The radiator was cleaned and tested by a radiator shop and was declared by them to be good. The radiator hoses are good. The thermostat is a 180 degree unit and I tested it myself in a pan of water on the stove and it is good. I am using a fan shroud and 5 blade fan, and running a 50/50 mixture. Stock engine with a Weber 32/36. Fan belt appears tight enough. Timing is on the money. The only other clue may be in the speed of driving. The first trip out, I did not go over about 40 mph, but I did climb the mountain. The second trip out, was more 50-55 mph for a while. Perhaps the radiator can not handle the increased demand at higher speeds? Some things I can try are to run it without a thermostat and see if that helps. Also, I will pay more attention to the possible connection to speed. I flushed the system a couple of months ago, but plan to do it again. Any insight before I do would be greatly appreciated. Fred

. . . some basics first, you've already said that the cooling parts are deemed in good order, so driving speeds, at least those you're reporting, have nothing to do with your "problem" . . . if anything, the faster you go, the more air that flows through the radiator, the better it cools . . . within reason, and yours were definitely WELL WITHIN!!

Your interpretation of temp gauge "normal" and "overheat" indications is where a lot of your perceived "overheating" problem lies, IMO! Allow me to explain . . .

. . . as you can see, what you saw as "normal" is actually on the cool side, with the "lower 1/4 of the gauge" also being too cool and not good for the engine . . . and a good indicator of a "stuck open" T-stat too!

What you "saw" as "overheating" is actually a fairly "normal" operating range for your typical 180° T-stat . . . After flushing and refilling the engine with coolant, did you run it through several heat cycles to "burp" any coolant air pockets in the engine BEFORE you took it for that first outing?

All that said, I would change the T-stat for a new one as already suggested, just to be sure! . . . oh BTW, have you checked/replaced your radiator cap . . . ever?! . . . very often completely ignored!!

[OriginalOpelGTOwner]

I just went over my stock cooling system last fall. My 180F thermostat reads 180 on my temperature gauge as per the above post. The system holds 6 quarts when filling the radiator to the proper level. My experience is when I pull the lower radiator hose to drain the system 1 quart of coolant is always left behind. I carefully flush the system until only water is remaining. I add 3 quarts of standard green antifreeze then 2 quarts of distilled water for a total of 6 quarts which includes the one quart left after flushing. If you overfill the system the radiator will overflow mainly during a hot soak with the engine off on a hot day after a long drive. I do not have an overflow bottle installed. Still stock configuration.

[gtblast]

Many thanks to all of those that responded to my post. The thermostat seemed to be the overwhelming suggestion, so today I changed it out with a new 180 degree unit. I was also questioning if the gauge was reading correctly, so I also changed out the temperature sensor with another one I had in a spare engine. The gauge now reads correctly, and with the new thermostat, it reads right where it should when the engine is up to operating temperature. Tomorrow or Wed., I will take it for a couple of test drives and see how it behaves. I will report back how it goes.
Fred

[gtblast]

As reported yesterday, I changed out the thermostat with a new 180 degree one, and also changed out the temperature sensor. Today, it was nice and warm, low 80's, so I took it for a test drive. Here is what happened.

I started out cold and watched the temp gauge as it climbed up to where I thought the thermostat should open. It acted normal, reaching a point on the gauge between the 176 degree and 194 degree mark, and seemed to cycle in that area. About 10 or 12 miles into the trip, the temp began to creep up slowly, past the 194 degree mark. As I continued to drive, it continued to creep up ever so slowly to the 212 degree mark and beyond. By this time I was headed home and only had a few miles to go. It continued to creep up past the 212 degree mark so that by the time I arrived home, it was just at the red zone on the guage. Once home, I popped the hood and found that the overflow was full, which had been nearly empty when I started, but the engine did not seem to be too hot. I shut the engine off, with no percolating or steaming.

What troubles me about this is that the indications are that the engine temperature is fine for a long time, long after the themostat has opened, and then it begins to go up.
Any additional thoughts?
Fred

[tomking]

Do you have any indications you are running lean?

[tekenaar]

Originally Posted by tekenaar . . . have you checked/replaced your radiator cap . . . ever?! . . . very often completely ignored!!

. . . as previously said . . . above.

[Tru-Craft]

Don't know the condition of your engine?
Is this a fresh rebuild?
Did this just start happening?

[gtblast]

Originally Posted by tomking Do you have any indications you are running lean?

I have a Weber 32/36 on this vehicle and it may be a bit lean. I do not have the jet numbers in front of me from when I rebuilt the Weber, but I can tell you that the color of the plugs look perfect and not too lean.

[gtblast]

Originally Posted by tekenaar . . . as previously said . . . above.

Sorry, I did not answer earlier. Yes, I have a new radiator cap. It was a must so I could use an overflow tank.

[gtblast]

Originally Posted by Tru-Craft Don't know the condition of your engine? Is this a fresh rebuild? Did this just start happening?

This is a project car I bought in mid Spring. It had not been running for years. It is now on the road and safe to drive, having taken care of the brakes, steering, lights, etc. I do not know the actual miles on the engine, but I do know it has hydraulic lifters and appears to be the lower compression. It starts and runs great, and currently has only two problems, this coolant issue and an oil leak. As mentioned before, when working on other things, I had the radiator out and checked, and flushed the block. I have been driving this car more and more, trying to build up my confidence and work out the bugs. Only lately, have I been driving it for longer periods of time, and this is when the overheating issue started to show up.

[deaner]

Originally Posted by gtblast The coolant overflow bottle was almost full, so I shut it off and let it cool down some. When I shut it off, it began to percolate and belch steam out of the overflow container.

I had a Toyota truck that did this. It really never overheated but would percolate and belch steam. Turned out to be the water pump, somehow it was sucking just enough air through the shaft. Also I have seen new caps fail, what pressure cap are you using? They also can be tested.

If it's still doing this. You have a problem. But if it's running around 200-210 this is expected on a hot day driving up hills. If it's getting too hot, I would suspect the radiator. Even used cleaned radiators can be bad. Nothing like a new one. Sound's like you just don't have enough cooling available. I have found that Hi performance Opel's can heat up on hot day's. That's why I've always had stock radiators upgraded to more cooling area. It's worth the insurance.

HTH

[gtblast]

Originally Posted by deaner I had a Toyota truck that did this. It really never overheated but would percolate and belch steam. Turned out to be the water pump, somehow it was sucking just enough air through the shaft. Also I have seen new caps fail, what pressure cap are you using? They also can be tested. If it's still doing this. You have a problem. But if it's running around 200-210 this is expected on a hot day driving up hills. If it's getting too hot, I would suspect the radiator. Even used cleaned radiators can be bad. Nothing like a new one. Sound's like you just don't have enough cooling available. I have found that Hi performance Opel's can heat up on hot day's. That's why I've always had stock radiators upgraded to more cooling area. It's worth the insurance. HTH

I am running a new 7# radiator cap. On all my older cars, muscle cars and performance cars alike, I have always switched to a 7# cap, as it is a little more friendly towards the old heater cores and radiators. Never had any problems with that, no boiling or coolant loss issues.

I am going with Tomking a little in that I might be running a bit lean which would drive the temperature up. Also, I am with you in thinking that the old radiator might be just borderline, and is fine for low speed local driving, but not enough cooling when I push it faster and harder. Perhaps a combination of both.

By the way, it has been hours since I drove the car and I just checked, and it has sucked all the coolant back into the system from the overflow tank, so that appears to be working normal.

[Dennis Texas]

just curious, is the overflow container for radiator coolant in front of the radiator blocking air flow?

[gtblast]

Originally Posted by Dennis Texas just curious, is the overflow container for radiator coolant in front of the radiator blocking air flow?

Since I am using a Weber 32/36, I have a small air cleaner just on top of the carb., so I removed the stock air cleaner. I mounted an Opel GT windshield washer bottle and bracket just to the side of where the normal air cleaner snout would stick through the core support. So, it is completely tucked away and out of the air path to the radiator, but excellent question!!

[deaner]

Originally Posted by gtblast I am running a new 7# radiator cap. On all my older cars, muscle cars and performance cars alike, I have always switched to a 7# cap, as it is a little more friendly towards the old heater cores and radiators. Never had any problems with that, no boiling or coolant loss issues.

I think I would rebuild your radiator , and have your local radiator shop add more rows. They can customize anything.
The factory list 13.2-15.2 (why the .2 ???) 7 lbs. of pressure is just not enough. 7 lbs. may work on cars that have oversized radiators to begin with.