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Discussion Starter · #1 ·
My son had one of my e46s and it had a coolant leak. Took it to the shop and they replaced the radiator and the lower coolant hose. No need for commentary about DIY - I can't do it when I live 1500 miles away.

we drove the next day about 100 miles and the car overheated - steam billowing out of the hood. The bleeder screw was a bit mangled and steam was pouring out.

my question is what would cause this? Presuming I didn't destroy the engine, I would like to repair it, so I will replace the upper radiator hose.

could it have been overfilling or bad bleeding?
 

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The bleeder screw was a bit mangled and steam was pouring out.

my question is what would cause this? Presuming I didn't destroy the engine, I would like to repair it, so I will replace the upper radiator hose.

could it have been overfilling or bad bleeding?
The bleeder screw is leaking and this is the main issue. There are other potential cause for the overheating, such as bad bleeding, but over filled does not cause overheating. Was the red light turned on on the temp gauge? If yes then it's a serious problem if head is cracked.

Btw, there is no need to tighten the bleeder too hard; stop turning whenever the o-ring is below the hole rim.
 

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Who knows what caused the overheat 100 miles after a repair and a bleed...that's a bit odd..if it was a bad bleed, I think it would have overheated much sooner.

Did it occur at speed? In traffic?

Whenever I open the cooling system for a repair... and after I fix and bleed it ...I drive for days with the actual coolant temp shown on the cluster sub-menu...and watch it like a hawk... I suggest you show your son how to do this...the coolant temp gauge as programmed from the factory is nearly useless.

Hopefully you/he saved it in time...keep an eye out for coolant loss.
 

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Discussion Starter · #6 ·
It was at 80mph on open freeway.

I suspect either the bleed screw wasn't fully seated or it was cross-threaded. There was a lot of melted plastic around the threaded area of the hose fitting suggesting hot coolant coming out for a significant period before it hit a tipping point.

Put a new upper radiator hose in and have driven it 200 miles with OBDFusion on and it is cooling perfectly.
 

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2003 M3 6MT Slicktop
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we drove the next day about 100 miles and the car overheated - steam billowing out of the hood. The bleeder screw was a bit mangled and steam was pouring out.
sounds like the bleeder screw which is plastic either broke or was leaking. causing the system to not be pressurized and poor steam from it.
you can just replace the plastic bleeder screw. you can even buy some made if brass. less prone to heat brittling. but you don’t know yet if the top hose was cross treaded. so perhaps a new top hose is warranted.
good chance you’re fine
 

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I replaced the entire upper hose. The threaded opening was pretty melted by the escaping steam. Works perfectly now.
nice to hear 👍🏻
if you did it yourself make sure the connections are tight between hoses, use only bmw hoses for best fit, bleed properly and keep a good eye on the temp for a few drive cycles.
 

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Discussion Starter · #13 ·
I love to see a pic of the melted thing.
Don’t think it damaged by hot steam; human did that trying to fix the leaking after realizing it was cross threaded.
It was 100% damaged by the heat - it had plastic filaments around the opening. That is not to say that the tech didn't introduce the leak, either by cross-threading or not tightening, but the steam definitely compromised the plastic:

Automotive tire Hood Water Flash photography Automotive design

Automotive tire Automotive lighting Hood Motor vehicle Water

Hood Liquid Automotive lighting Automotive tire Water
 

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Discussion Starter · #14 ·
nice to hear 👍🏻
if you did it yourself make sure the connections are tight between hoses, use only bmw hoses for best fit, bleed properly and keep a good eye on the temp for a few drive cycles.
Yep. Definitely not my first BMW cooling system rodeo ;)
It was fun doing the fix in my in-laws' driveway, however.
 

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It was 100% damaged by the heat - it had plastic filaments around the opening. That is not to say that the tech didn't introduce the leak, either by cross-threading or not tightening, but the steam definitely compromised the plastic:
No need to see the pic with all the steam and smoke as these cause the bleeder part out of focus. If you still have the hose, post a good focused pic of it. The steam is not hotter than the coolant, and the hose was design for this and so I don't think it was melted by the hot steam.
 
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