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Overheating but not really? Air in system or other problem? Need help diagnosing by cebix
Started on: 10-31-2019 03:34 PM
Replies: 138 (2043 views)
Last post by: Patrick on 11-26-2020 05:31 PM
Patrick
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Report this Post01-12-2020 05:52 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by cebix:

So I took the rad cap off (maybe shouldn't have done that?) to see if the hose is flowing. It is. I'm wondering if I might have messed up the burping by removing the rad cap and introducing air back to the system. Is that possible?


On level ground, the rad cap is not the highest point of the Fiero's coolant system. Check your coolant level in the system by removing the thermostat housing cap. Also make sure of course that coolant is at the proper level in the reservoir.

It wouldn't hurt to burp it one more time... but in the future leave the rad cap alone!
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cebix
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Report this Post01-13-2020 11:17 AM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
All the old symptoms came back...

The reservoir tank filled up an inch moments after engine shutdown. So I'm guessing back pressure because of a clog. Damn this thing must be still clogged somewhere. I just can't believe it ran so well the first day - it was textbook normal temperature behavior. I must be pretty bad at flushing this thing. I guess the symptoms don't mean air in the system?
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olejoedad
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Report this Post01-13-2020 11:36 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
That would be perfectly normal.
The hot engine transfers heat to the coolant, causing it to expand.
This also burps the air out of the top of the radiator.
The level will drop as the car cools.

[This message has been edited by olejoedad (edited 01-13-2020).]

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cebix
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Report this Post01-13-2020 12:05 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
The level didn't rise when the engine was hot. Dead cold/operating temperature was exactly the same, rad cap and reservoir hose were both cold.

Only after I shut it down it filled up an inch in seconds and the rad cap and reservoir hose became warm.

Does that still make sense in an air bubble situation?
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cebix
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Report this Post01-15-2020 01:34 AM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
Story is now as follows:

1. Reservoir is being filled up an inch or so in a few seconds after hot engine shutoff. Level doesn't rise one bit when engine is running dead cold/hot.
2. The reservoir level is not dropping, it's not being sucked back in. Every heat cycle I have more coolant in the tank.

Could air be sucked in only through a loose overflow hose or basically any leak in the system anywhere? I'm not observing any coolant leaks whatsoever. If there's a small enough leak to not let coolant out but let air in, would a pressure tester show this?

[This message has been edited by cebix (edited 01-15-2020).]

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olejoedad
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Report this Post01-15-2020 07:34 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
The radiator to tank hose must be tight at both ends, free flowing and leak free.
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cebix
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Report this Post01-29-2020 02:51 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
Didn't really have much time to tinker with this issue so I'm just driving it and seeing no real improvement. Tightened some hoses, pretty sure there are no leaks. The coolant level still rises in the reservoir with each heat/cool cycle. I guess no self-burping is occuring so I have another question about it.

Since the system is "full" it's just not possible for me to get the thing running with the thermostat cap open. It sprays it out all over the place. How do I go about this? Should I drain some coolant and add it again while burping? Should I drain the system dry and refill it again? I just miss that one day it ran perfectly fine and I don't know if it was the one time I did the burping right. Thanks.
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Patrick
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Report this Post01-29-2020 03:36 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by cebix:

The coolant level still rises in the reservoir with each heat/cool cycle.


Well, the coolant level is supposed to rise during each heat cycle... but does the coolant level in the reservoir not also lower again when the engine cools down?

 
quote
Originally posted by cebix:

Since the system is "full" it's just not possible for me to get the thing running with the thermostat cap open. It sprays it out all over the place.


That's normal. Why do you wish to run the engine with the thermostat cap open.
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cebix
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Report this Post01-29-2020 04:12 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
I meant to run the engine with the thermostat cap off just during burping. It's not possible now even with the rear elevated (about 5 inches I'm guessing).

When I tightened some hoses and burped again the system about two weeks ago the coolant level was rising when hot and was lowering when cold, so it was operating normally. I'm checking the tank level every time I drive cold, hot and immediately after engine shutoff.

3-4 cycles after that the level was rising still when hot but lowering less and less back into the system. 2-3 cycles later it does _not_ go up when hot. Only goes up a few seconds after shutdown. Hissing can be heard from the rad cap when it does this. Now it's not lowering back almost anymore at all.

Two weeks ago the tank was halfway full cold. Now it's at the full line when cold in about let's say... 6-8 cycles? Didn't add any coolant to that tank manually, it filled up on its own. Does this give you guys any ideas on what to look for next? I though I would have had it with fixing this system but I'm now genuinely intrigued.
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Report this Post01-29-2020 04:28 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by cebix:

I meant to run the engine with the thermostat cap off just during burping.


Again I ask why? That isn't the way to burp the system.

 
quote
Originally posted by cebix:

Now it's not lowering back almost anymore at all.


I guess the question is whether the coolant is for some reason being prevented from being drawn back into the radiator while cooling down... or is there something (air) being added to the cooling system (from an internally cracked head?) that's displacing the coolant?

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

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cebix
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Report this Post01-29-2020 04:45 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
(...)"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).]

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Report this Post08-01-2020 01:14 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
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...
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Report this Post08-01-2020 10:57 PM Click Here to See the Profile for Mike in SydneySend a Private Message to Mike in SydneyEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.

------------------
Mike in Sydney

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cebix
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Report this Post08-02-2020 04:00 AM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
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).]

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Patrick
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Report this Post08-02-2020 04:14 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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.
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cebix
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Report this Post08-02-2020 05:30 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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.
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cebix
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Report this Post10-15-2020 03:46 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
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?
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cebix
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Report this Post11-26-2020 05:06 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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Patrick
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Report this Post11-26-2020 05:31 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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.
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