Overheating/coolant loss issue

E28 technical advice asked and given! Troubleshooting, modifications and more.
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stuartinmn
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Joined: Feb 12, 2006 12:00 PM
Location: Minneapolis

Overheating/coolant loss issue

Post by stuartinmn »

The other day I was out driving around on errands when it was around 95F outside. The temp gauge was a little past the center point but not into the danger zone, and the car was running fine. I came home, parked in the garage and went inside. The next day I went out to the garage and noticed the floor was damp so I opened the hood to see what was going on, and found that the overflow tank was empty, I mean totally empty.

I can accept the idea that after I parked the car it built up enough heat and pressure to blow some coolant out the overflow hose, but I'd think there still should have been some left in bottom of the overflow tank. Can the system discharge coolant with enough force to totally empty the tank?

I looked around and couldn't find any evidence of leaks or failed hoses anywhere. The only signs were some drops of coolant on the lid for the power steering reservoir - there's a crack in the overflow hose right where it connects to the overflow tank, which is right next to the power steering reservoir. I need to fix that but it wouldn't cause a leak, and it does show that there was a discharge from the overflow.

I did have a new water pump put in a couple weeks ago, but I didn't see any signs of leaks from it and it seems to have been working okay so I don't think that's related. I suppose the next step is to simply fill it up again and then run it for a while to make sure the temp gauge stays in the normal range and there are no leaks, but I wanted to ask first to see if anyone else has experienced this.
kojo96
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Location: Pleasanton CA

Re: Overheating/coolant loss issue

Post by kojo96 »

Check the water pump pulley and belt to make sure it's good amd not loose.

I'd fill the tank and make sure to bleed the system before just hopping in and driving it. There's a very good chance it'll take in air and that's the last thing you want after what just happened.

Fill, bleed and let it idle up to temp and pressure test the system before driving.
Mike W.
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Re: Overheating/coolant loss issue

Post by Mike W. »

That little 8MM bypass hose does carry coolant when the car is running, along with being a breather. There is a continuous flow thru it, not at high pressure per se, but still the normal system pressure. While Kojo's suggestion about bleeding is a good one, I wouldn't be surprised if you have a mist leak from that hose, which in time would cause it to be low.
kojo96
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Re: Overheating/coolant loss issue

Post by kojo96 »

Is this the E28 you were driving in Stuart? I'd be really cautious about driving it without fully understanding what the issue is. It's also odd that the low coolant light didn't throw a warning.
I may be wrong but is this the car that had a slight crack in the cylinder head?
stuartinmn
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Joined: Feb 12, 2006 12:00 PM
Location: Minneapolis

Re: Overheating/coolant loss issue

Post by stuartinmn »

I was talking about the drain hose that exits under the car, not the bypass hose, so there's only flow in it when the radiator cap bleeds off pressure.

I observed all this before trying to start the car, the low coolant light is still functional. No cracks in the cylinder head. When the new water pump was installed a couple weeks ago the repair shop did a pressure test, and the only leak they found was from the old water pump.

What I'm saying is the system was full of coolant the day before when I parked the car in the garage. It puked coolant after it was parked, which I discovered the next day when I returned to the garage.

Edited to add: Well, I refilled the reservoir, started the car, and let it run until it reached standard operating temperature. The tamp gauge stayed there, and I saw no leaks or signs of airlock in the system. So, I guess I'll just have to see...I'll drive it around locally for a few days and keep an eye on the coolant level and the temp gauge.
garageboy
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Re: Overheating/coolant loss issue

Post by garageboy »

Did you bleed it through the thermostat housing??

And this sounds PRECISELY like a cracked head (but I don't wanna be the one to be the bringer of bad news). Don't ask me how I know. :(
Mike W.
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Re: Overheating/coolant loss issue

Post by Mike W. »

garageboy wrote: Jun 29, 2022 1:42 AM Did you bleed it through the thermostat housing??

And this sounds PRECISELY like a cracked head (but I don't wanna be the one to be the bringer of bad news). Don't ask me how I know. :(
A cracked head is fairly easy to diagnosis, I can say that having had a few. You look in the expansion tank with the engine running. Just at idle is fine. There will be turbulence in there, looking inside with the cap off, but there shouldn't be bubbles. The little 8MM line off the top of the radiator does shoot coolant back into the tank, and it can be a little hard to tell as water is moving all around in there, but there shouldn't be bubbles. They would be coming from combustion gasses being pushed thru the crack in the head by the ex valve seat to the water jacketing in the head.
garageboy
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Re: Overheating/coolant loss issue

Post by garageboy »

Well, when Ben Thongsai diagnosed my cracked head on my earlier E28, he said, get the car warm and then pop off the valve cover...

I did exactly as he instructed.... then he walked over, grabbed the upper radiator hose, squeezed it, and we got to watch the coolant squeeze through the crack on top of the head (between cyl 5 and 6 as I recall where all early eta heads failed) that we would never have seen otherwise. :laugh:
Mike W.
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Re: Overheating/coolant loss issue

Post by Mike W. »

garageboy wrote: Jun 29, 2022 5:13 PM Well, when Ben Thongsai diagnosed my cracked head on my earlier E28, he said, get the car warm and then pop off the valve cover...

I did exactly as he instructed.... then he walked over, grabbed the upper radiator hose, squeezed it, and we got to watch the coolant squeeze through the crack on top of the head (between cyl 5 and 6 as I recall where all early eta heads failed) that we would never have seen otherwise. :laugh:
Oh, we're speaking different languages. I'm in M30 and you're in M20. I guess they crack in different places. Although I have heard of B35 heads cracking as you describe, although I've not heard of troubleshooting that way.
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