Overheating but not really? Air in system or other problem? Need help diagnosing (Page 14/14)
cebix JAN 29, 04:45 PM
(...)"Put thermostat cap on and turn just barely enough to hold cap on."(...)

Man, I'm an idiot. I somehow remembered this another way and was burping always with the cap off and put aside so I could see the burping in the coolant... I did this every time. And it kind of worked I guess until it got so full it was blowing out. Sorry about that, it was probably mentioned in some other burping instructions and it just stayed in my head.

EDIT: Yeah, I was holding the cap barely on when starting the engine but once it started I was removing it altogether for those 30 seconds until shutoff and revving ocasionally.

As for the second question... I have no idea. I can only say for sure that I had this problem before the engine was rebuilt. The shop supposedly pressure checked the head during the rebuild. But the coolant was flowing back nicely those few cycles and it just stopped again. And not to mention the new radiator, new heater core installed just a month or so ago. Also no other symptoms of a cracked head that I can tell.

[This message has been edited by cebix (edited 01-29-2020).]

cebix AUG 01, 01:14 PM
A little update.

Nothing really has changed, been driving like this the whole time revving it slightly in traffic if the needle goes too high.

However I noticed a change - it's the first time we've had these temperatures since my engine rebuild (>86F) and when I drive the car in this heat... it runs perfect. No sudden needle movements, temps stay rock solid. Like a normal car should. Starting it in the morning when it's colder the engine temp still likes to go up... Starting it after work again with >86F heat it runs great again.

I'm thinking it's a manifold gasket leak now and/or poor pairing to the block, maybe even a cracked inside manifold? Does this change in behavior say anything about my problem? Heat outside, car runs great. Wheather is colder, car wants to overheat...
Mike in Sydney AUG 01, 10:57 PM
Interesting problem...It sounds like the thermostat is slow opening when the car is cold. What temperature stat do you have? A higher temp 'stat will open slower. If the car is cold (morning start-up, setting in the cold, etc.) it would take longer to getup to temp and open than it would if the car was warm (warm day, recent driving, etc.).

I expect you know this already but you can check the temp where the stat opens by taking it out and putting it in a pot of water on the stove with a cooking thermometer. I put mine in an old whiskey tumbler in the pot to keep the thermostat from being in direct contact with the bottom of the pot. Turn the burner on and slowly bring the water temperature up. You'll see when the "plug" in the 'stat opens.

BTW, I had a problem burping the radiator on my '86 2.8 GT. I got rid of it by parking the car with the engine well above the radiator. Our drive way was short but it was a 40-degree incline. I backed the car up the drive opened the front radiator and overflow tank and filled the system from the engine without the t'stat until the coolant was running out of the radiator. I then put the radiator cap on and the overflow tank cap back on and added coolant to the t'stat housing until it reach midway up the neck. I cranked the car and let it idle for ten minutes while watching. Saw a couple of big "burps" and the coolant level dropped in the t'stat housing. I topped up the coolant and let it idle for a few more minutes. No more burps so I replaced the t'stat with a 180-degree thermostat. Haven't had an issue since.

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Mike in Sydney

cebix AUG 02, 04:00 AM
I wonder if it is indeed a burping problem.

I have the standard 195F Stant Superstat. Did the boiling pot water test - it's opening nice and wide. Many posts say the car should burp pretty much itself after a few heat/cool cycles and I've done a hundred of those easily since the engine rebuild.

[This message has been edited by cebix (edited 08-02-2020).]

Patrick AUG 02, 04:14 PM

quote
Originally posted by cebix:

I wonder if it is indeed a burping problem.



As important as "burping" the system may be, it's not something that needs to be done over and over and over again.

I'm more inclined to suspect that it's a coolant circulation problem. Whether that's due to a slipping belt, loose impeller, blockage in system (radiator, engine block, coolant tubes), I don't know.
cebix AUG 02, 05:30 PM

quote
Originally posted by Patrick:

As important as "burping" the system may be, it's not something that needs to be done over and over and over again.

I'm more inclined to suspect that it's a coolant circulation problem. Whether that's due to a slipping belt, loose impeller, blockage in system (radiator, engine block, coolant tubes), I don't know.



Yup, been fighting this for quite some time now. Only thing left to do is tear down the whole system, poke through every tube.
cebix OCT 15, 03:46 PM
Quick follow up on this. Yeah the problem's still there, however...

I noticed a slight but sudden improvement after torquing down the intake manifold bolts. So I think I've got coolant leaking into the cylinders either from the gasket or internally from the manifold.

Is there a quick bypass test I can do? Is plugging the coolant tube that flows into the intake going to show improvement? Or does the coolant flow the other way around?
cebix NOV 26, 05:06 PM
Alright here's an update.

Took the car to a shop and told 'em what I think and that they should check the manifold first.

Turns out there was a small leak into the intake. They redid the gasket, torqued down the manifold to spec and so far... Seems like it's fixed.

Will update if turns out it's not it but for now it seems there was indeed a intake manifold gasket leak causing all these problems.

Thanks for you suggestions all this time, much appreciated.
Patrick NOV 26, 05:31 PM

quote
Originally posted by cebix:

Will update if turns out it's not it but for now it seems there was indeed a intake manifold gasket leak causing all these problems.



I hope you're right... but looking over all the problems you reported in this thread, I can't help but wonder how a coolant leak into the intake would cause all these issues... unless the coolant reservoir was being sucked dry as the coolant level dropped, and air was being drawn into the system.

Keep us informed of any new developments.