E36 M3 Cooling System Pressurization

[MyNameJeff]

Good evening all,

My e36 M3 has been having some cooling system has been having some issues recently. To preface this, I bought the car with ~80k miles on it, replaced all components of the cooling system known to fail. CSF radiator, water pump, upper and lower radiator hoses etc. but I cannot seem to get air out of the system.

I can open the expansion tank, the level will rise to the KALT line, and drive it HARD for 20 minutes or so and the cooling system will have no pressure the next morning, but if I drive it for ~2 hours, the level drops while the system is under pressure and operating temperature until the expansion tank is opened and the level rises back up to the KALT line when cold. I have ran a block test within the expansion tank on initial start up and at operating temp at 2-3k rpms and the results were negative for combustion gasses.

I am at my wits end with this and just want confirmation that the head-gasket or head is cracked because this cannot be normal. I have bled the system multiple times and seem to have gotten all the air out. I think the installation of a euro self bleeding system may help with residual air in the system but I am not sure.

Any help is appreciated, thank you.

[GG///M3]

I’ve heard of guys having issues with those radiators on e46 m3’s. Get a stock replacement or a better brand


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[ScotcH]

It's not hard to bleed. Did you drill a 1/8" hole at the top of the Tstat? With that done, you literally just fill it until it will tkae no more water (like to the brim full). Close it, and forget it. If next day it's pressurized or below the fill line, you have blown headgasket, likely at the back of #6 cyl.

[MyNameJeff]

I’ll look into radiator alternative, but I was under the impression CSF was pretty good quality.

For the bleeding procedure, I’m not sure exactly if I did it correctly. I did not drill a hole in the thermostat but maybe I’ll tear it down and change that out.

For what it’s worth I just got back from a 400 mile round trip with the car and there was no overheating, loss of heat in the cabin just hoses that seem a little harder than normal. No loss in coolant either.

[ScotcH]

so if you're not overheating, why are you worried about it? The CSF rad is fine ... I mean they're cheap, but they'll do the job just fine unless you're like in the middle of the desert and trying to race.

[mike.bmw]

I had a similar issue, to the point where coolant was leaking past the hose clamps due to the pressure. I had replaced the water pump, all the hoses, and installed a CSF radiator. It got bad enough that the cooling system still had pressure the next morning. I had a leak down test performed and it confirmed the head gasket was likely bad. I replaced the head gasket and it solved the issue... though I still check the cooling system pressure/level on an almost daily basis.

I wrote more detail in these articles for BimmerLife:

https://bimmerlife.com/2023/06/28/breathing-new-life-into-a-classic-m3-project-concord-loses-its-head/

https://bimmerlife.com/2023/07/18/breathing-new-life-into-a-classic-m3-project-concord-lives/

[MyNameJeff]

Great write up mike. I too am from the DMV area and might have to reach out to the mobile mechanic you mentioned in your article for some assistance.

In the meantime I will do a leak down test for confirmation of the head gasket failure. Crossing my fingers that my head turns out okay like your experience.

Thanks!

[R Shaffner]

This thread might help, when we're talking about the stock system. I don't know about the M3 or that after-market radiator specifically.

https://www.bimmerforums.com/forum/showthread.php?2392287-BMW-Expansion-Tanks-Caps-and-Bleeding-Explained

What do you mean when you say thee coolant level "rises to the Kalt line?" Is that radiator plumbing different than stock in some way?

[MyNameJeff]

I’ll have to get a look into that thread. But for more explanation on what I mean about the coolant level rising, it seems like there is an excess of gas pressure at the top of the expansion tank. When the cap is released there is a hiss and the coolant level rises as if gas is exiting from the cooling system.

[ScotcH]

Well yeah ... that's pressurized. So yeah, that's going to be HG.

[propcar]

I have a CSF (all aluminum) radiator and haven't had any issues with. The BEHR Z3-S54 weren't available at the time of the headgasket job.

When the HG went, there was no mixing of fluids like milky coolant or anything, but it would just start to overheat while idling.