Odd overheating problem

[blancojp]

Originally Posted by gtblast I figured that 7# radiator cap would get your attention!! This afternoon, I took it out for another spin, about the same length as earlier in the day. All was good until about 3/4 the way through the run, then the temp started to creep up. By the time I got home, it was above the 212 degree mark and slowly climbing. I popped the hood and the top radiator tank and hose were hot, and the bottom tank and hose were just as hot! So, I doubled the radiator pressure cap rating, but still got the same results. Back to square one.

This was the same problem I had with a '72 1.9L engine and there is a good thread on it.

End result was, changed the head gasket, added the several cooling holes and went away. As a matter of fact, the engine never went over 180 degrees with proper coolant ever again.

http://www.opelgt.com/forums/6b-cool...ht=overheating

[blancojp]

Originally Posted by wrench459 The temp drop from top to bottom of the radiator should be at least 30 degrees. You've got an air flow or plugged rad. or a slightly blown headgasket

Perhaps the gasket has more voltage than required???

[tekenaar]

Originally Posted by gtblast I figured that 7# radiator cap would get your attention!! Yes, I am old enough to remember the pressure cooker my mother used, with the rattling weight on top to maintain the proper pressure. Shows you how old I am!! Anyway, as promised, this morning before I took the GT out for a run, I changed the pressure cap from a 7# cap to a 13# cap. You guys with your pressure cap physics convinced me. First, I started the car in my driveway and let it run until the engine came up to temp. Just like clock work, the thermostat opened at 180 degrees, all looks good. So, I took it out for a good run, about 30 minutes, at least 50% of it at 50 mph or more. The temp stayed right where it should, between the 176 and 194 degree marks. When I arrived home, I popped the hood. The top radiator hose and tank were hot, but the bottom tank and hose were much cooler. Looks good, so I am thinking this radiator cap pressure issue must be it. This afternoon, I took it out for another spin, about the same length as earlier in the day. All was good until about 3/4 the way through the run, then the temp started to creep up. By the time I got home, it was above the 212 degree mark and slowly climbing. I popped the hood and the top radiator tank and hose were hot, and the bottom tank and hose were just as hot! So, I doubled the radiator pressure cap rating, but still got the same results. Back to square one.

. . . OK, let's analyze that last papragraph in detail . . . up to the 3/4 point of your last run, coolant system is operating normally, as expected.

In summary, each slight coolant system temp drop is caused by hotter than 180° engine coolant opening the T-stat and allowing this coolant to flow into the top radiator tank to replace colder coolant drawn from the radiator's bottom tank and pushed into the engine by the pump.

When T-stat "sees" that the engine coolant temp drops below 180°, it will close again and stop coolant flow into engine and out to radiator allowing the engine heat to raise temp once again, repeating the process. This is defined as "normal operation."

After the 3/4 point of your last run, the system coolant temp continues to rise above "normal", uncontrolled any longer, which tells me that "system" coolant flow is interrupted, i.e. has ceased! This is supported by the fact that you state that both top and bottom radiator hoses were at the same temp when you got back . . . no flow through radiator!

There are but two things that control all coolant flow, the T-stat and pump! . . . and I don't think the pump magically stops functioning of it's own accord! If just me, I'd run the test again without a T-stat . . .

Also, 50 MPH in top gear is ~2500RPM . . . widely considered "just off-idle" in most Opel camps, so it's not like you're even close to pushing the envelope stressing the engine here!!

[tekenaar]

Originally Posted by wrench459 The temp drop from top to bottom of the radiator should be at least 30 degrees. You've got an air flow or plugged rad. or a slightly blown headgasket

. . . try starting your engine in the driveway without a radiator cap and look in the radiator for bubbles while running . . . there shouldn't be any, of course!

[oldopelguy]

Originally Posted by tekenaar . I'd run the test again without a T-stat . .

I'd modify that a bit myself, and swap in either the 5/8" or 3/4" flat washer from the hardware store that's the same OD as the thermostat when you take it out. For some reason I always have best luck with no thermostat if I keep just enough resistance to flow there to slow the coolant down as it drops down through the radiator. There's a lot of guys on both sides of that debate, though, so it's up to you which side you believe.

FWIW, my 4-door Kadett right now runs 75mph just fine, all day long, but at 78 it develops just enough heat that the temp gauge starts creeping up until I slow down. It's certaily due to the radiator being just barely enough, and it's fine with me for now, but I will be upgrading the radiator before I charge the AC system with freon. It's not at all hard for me to believe the radiator would not be up to the task of even a stock Opel motor.

[wrench459]

Originally Posted by blancojp You are kidding, right?

Nope I've seen it many times.
The cooling system turning into a small battery.

[trlmr]

the process is called electrolysis (hope I spelled it right) and is usually checked with a ph strip that you can get at most diesel motor supply outfits. the antifreeze builds up an electrical charge that is neutralized with additives or in the case of most diesel engines a coolant filter that contains the nessessary additives. It is a concern on diesel engines because the acidity of the coolant will actually eat holes in the cylinder liners, and to a lesser degree foul up the radiator. But, usually not much of a concern on gasoline engines. This is the reason the oem's want you to change coolant

[kent]

FWIW, my 4-door Kadett right now runs 75mph just fine, all day long, but at 78 it develops just enough heat that the temp gauge starts creeping up until I slow down. It's certaily due to the radiator being just barely enough, and it's fine with me for now, but I will be upgrading the radiator before I charge the AC system with freon. It's not at all hard for me to believe the radiator would not be up to the task of even a stock Opel motor.[/quote]

My first gt did this back when the limit was 55 she would heat way up at 55 but would cool right down at 60

[Dennis Texas]

another question ...you don't happen to have a lower gear in the rear end by any chance.

[ungermm]

Originally Posted by gtblast Tom, Your point about the radiator is a good one. I believe the radiator shop only filled the radiator and pressure tested it, and flushed it out with water. I am certain they did not boil it or hot tank it, and they did not rod it.

It's hard to tell if the radiator is at fault. When you see a lot of crud or rust in it you have a pretty good clue it's bad. However, you wouldn't be able to know that with the offset inlet neck. If the radiator shop did a pressure test and it holds, you have eliminated the possibility of leaks in it. Plus, you would most likely have noticed leakage when it got hot. The other variable is the amount of flow through the radiator. I've done the garden hose trick through one of the hose fittings and watch to see how it flows through the other. However, if you have a condition where the radiator is marginally good, that wouldn't be good enough information. I would do as already suggested and run it without the thermostat. But, I'm thinking you will probably need another radiator.
It's been suggested that you might have head gasket issues. My experience is that you will see a loss of coolant and/or moist exhaust if that condition existed.
Water pump? I don't think so. But it just reminded me of my old Jeep when I put in a new water pump and the temp gauge climbed quickly after starting it. That was because the fins of the new impeller were facing the wrong direction.
Jerry

[gtblast]

Here is an update on the overheating issue with my GT.

I went back and looked at my receipt from when I had the radiator shop check out my radiator. It clearly states that they power washed it and flushed both ways, and visually tested for flow and it was good. Also no leaks tested to 15 pounds.

So, I decided to flush the system. Some months back, I had put in some Barr's Leak sealant and water pump lube just to make sure there were no leaks. Of course, the Barr's Leak turns the coolant somewhat brown. However, when I drained and flushed it the first time, the coolant came out looking like hot chocolate or bad coffee! I flushed it clean and added a cup of Washing soda and drove it around for a while. I drained it and flushed it several more times until it ran clear and no trace of the soda. I filled it with a 50/50 mix of glycol and water.

I took it for an extended spin and it seemed fine, and never got over the thermostat temp of roughly 180 degrees. This is part one.

The more I thought about it, I decided it was running a bit lean, and that may be contributing to the heating issue. So I dug up my notes from when I rebuilt the Weber 32/36. I had placed the 135 jet in the primary side and the 140 jet in the secondary side. The logic here was better gas mileage and it would go richer when the secondary opened. After some thought, I decided to swap the jets and put the richer 140 jet in the primary and the leaner 135 in the secondary. Once I did this, I took it out for a spin. The first thing I noticed is that I could feel a difference in the power, so I was sure I made the right choice by changing the jets around. Also, I had had a slight hesitation at the transition from idle to light throttle when cruising along. Now the hesitation was gone. Another step in the right direction. I have had it out for several longer spins since then with no problems. So, part two I am sure helped.

Now, the only part that is unknown is, if I cured the overheating issue with these steps I have taken, or is it just running cooler because all of a sudden Fall weather has arrived and it is now 30 degrees cooler outside than it was a week or so ago???

Either way, I have had it out on four good long runs in the last week and it has been fine. So, if there still is a problem, perhaps it will not show up again until next Spring/Summer. Many thanks to all of those that offered suggestions and insight.

[ddoyle]

I am glad it is working ok now, guess the real test will be when the weather heats up. I have read thru all the posts and would like to add a few things. The boiling point of a 50/50 mix (EG/water) is advertised to be 223F, 70/30 raises it to 235F. The point about the voltage in the coolant is a good one, but this condition normally leads to leaks caused by electrolsis, voltage/coolant action eats thru the metal, heater core usually the first victim. This cannot be checked with a PH strip, that is for measuring the acidity/aklynity of the coolant. The coolant filters and additive packages used on big rigs and commercial units have one main purpose, to extend the life of the coolant. Now my question is about the Barrs leak... that was added after the rad was checked out? Barrs leak is a good product, for emergency use to get you off the road. I have seen the insides of thousands of radiators, and bars leak will really plug coolant passages solid. The only way I know to get an accurate idea of flow in the radiator, pull the top tank, large water hose attached to bottom hose connection and see the flow or lack thru each tube. Sorry for the long post, hope someone got something out of this.

Dan

[trlmr]

Sorry, I was trying to keep it simple in my explanation of the coolant test. I attached the instruction to the test strips if anyone cares. It actually measures moly and nitrite levels. As the coolant flows around inside the engine it flows across dissimilar metals. Over time it does build up an electrical charge similar to a battery, so wrench459 is correct in what he says. The test lets you monitor the metals (moly in this case) and nitrites in suspension. The coolant additive contains the chemicals to keep things in balance and negates to electrical charge. Anyway I don't know if this interests anybody or not and it gets alittle off topic. If the moderator wants to delete it I won't take it personally.

I am waiting for UPS to deliver a part and I have too much time on my hands I guess
Tom

[gtblast]

Last weekend I took the GT on a 60 mile run. I went 30 miles out to go look at a 71 GT for sale, and 30 miles back. My GT ran great the entire trip, no overheating problems.

Yesterday, I took the GT out for a 24 mile run to meet some friends for lunch. I went out 12 miles and the car ran great. On the return trip, I stopped about half way and went to the bank. On the second half of the return trip, the temperature began to creep up. Once it got to about 212 degrees, I pulled off the road and looked it over. Everything seemed in order, but I did notice that the bottom of the radiator was almost as hot as the top to touch. I finished the drive home, and by the time I got home it was up to about 250 degrees on the gauge. I shut it off and it began to percolate and completely filled the overflow with coolant.

I looked at it a couple of hours later and it had sucked the coolant back into the system from the overflow tank.

So, it seems my recent flush and carburetor jet change did not help the problem. Odd, that this overheating problem seems to occur in a radom fashion, sometime it does, other times it does not. One day I can go on a 60 mile run with no problems, and another day I go 12 miles down the road and barely make it home.

[MICAH1]

Dang, Just when we thought it was safe to go back in the water JAWS returns!!!!! All that mileage with no problem then ..... it's back!!! Radiator blockage or thermostat sticking?? I know we went down this street before but did you change to another radiator just to test???

Just finished reading this entire story again ........ with a sharp eye on what Otto is saying. There is a point of pressure building up from blockage. Either the thermostat sticks, or there is a circulation issue somewhere in that radiator!!!! If you have a extra radiator install it and run a gradual road test. Won't hurt to run without a thermostat too.

Time for another edit..... Are you getting good heat inside the cabin. When the control is open it to is part of the coolant route......Yes???

[Redskinsjbs]

Are the air tempertures the same?

Does it ever rain?

I am just trying to see if there are other factors that change along with the overheating.