diagnosing and fixing aux fan... or more?

E28 technical advice asked and given! Troubleshooting, modifications and more.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Also just reread a detailed post on overheating from 2021 in which someone suggested removing the thermostat and running engine to see if it stayed cool with no thermostat = thermostat is broken.

No one responded that it was a bad/good idea, however It does sound easy. Any reason not to try that?

Thanks.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Wow. Senility may be taking hold. I replaced the pump and thermostat in 2018. I just searched my old posts. I will keep searching and reading. I just let it run for 20 minutes in the garage and gauge needle stayed horizontal. Hot water was moving through radiator, but slowly. Big temp differences were at input to thermostat (~90 degrees) and exit end of thermostat (~180 degrees). Temps on pump were steady. Makes me think the thermostat is not opening adequately when I drive the car. It otherwise didn’t overheat after 20 minutes idling in the garage.

Also, coolant surface level was again not turbulent before I shut it down, which would indicate ongoing blockage, as I understand it.
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Mar 17, 2023 6:38 PM Also just reread a detailed post on overheating from 2021 in which someone suggested removing the thermostat and running engine to see if it stayed cool with no thermostat = thermostat is broken.

No one responded that it was a bad/good idea, however It does sound easy. Any reason not to try that?
Yes, there's a big reason why you shouldn't try that -- with no thermostat, the coolant will "short" right back into the block and only a minimal amount will go towards the radiator.

The idea stems from a lack of understanding of the M30 cooling system compared to "standard" cooling systems. In the latter, the thermostat solely blocks flow to the radiator. In an M30, the thermostat directs flow, either 100% right back into the engine (fully cold) or 100% to the radiator (fully hot), and proportionally in between.

If you remove the thermostat, it's guaranteed to overheat.

BTW, please post that 2021 thread so I can post that it's a bad idea.
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Mar 17, 2023 6:08 PM I did just waste some money on 3 gallons of top brand coolant. 🙄
No, you didn't. Capture it when you drain the radiator so you can replace the thermostat, and pour it back in (filtered if necessary). You don't need to drain the block at this point. Just install the Fumoto valve next time you really do need to do a full replacement.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Shawn D. wrote: Mar 18, 2023 7:08 AM BTW, please post that 2021 thread so I can post that it's a bad idea.
viewtopic.php?p=1500264#p1500264

I copied the URL here, Shawn D. Did that work? It appears to not be regarding a M30.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Shawn D. wrote: Mar 18, 2023 7:11 AM
Mashford wrote: Mar 17, 2023 6:08 PM I did just waste some money on 3 gallons of top brand coolant. 🙄
No, you didn't. Capture it when you drain the radiator so you can replace the thermostat, and pour it back in (filtered if necessary). You don't need to drain the block at this point. Just install the Fumoto valve next time you really do need to do a full replacement.
Thank you.
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Mar 18, 2023 8:07 AM
Shawn D. wrote: Mar 18, 2023 7:08 AM BTW, please post that 2021 thread so I can post that it's a bad idea.
viewtopic.php?p=1500264#p1500264

I copied the URL here, Shawn D. Did that work? It appears to not be regarding a M30.
Yes, that worked. The second paragraph of the first post says "M30B34" and that's absolutely an M30 in the pictures.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Shawn D. wrote: Mar 18, 2023 7:05 PMYes, that worked. The second paragraph of the first post says "M30B34" and that's absolutely an M30 in the pictures.
Glad you caught that, Shawn D.!

Thank you.

Meanwhile, I did two more road tests to see what I might learn. On first, after 15-20 minutes the gauge stayed at vertical for 5-10 minutes and then started creeping up again to redline. I parked it. I road tested again today with more or less same results, except in addition to creeping up to redline — after holding vertical for 5-10 minutes — the cabin heater started blowing cold, then hot, then cold again and finally back to hot.

🤔

Could this be related to heater core, then, contrary to having ruled that out before?

I am ordering new thermostat now, regardless, to eliminate that possibility.

Thanks.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Also, I am trying to figure out the differences between the temperature ratings of the different thermostats available for my 535is M30 configuration. The 71 degrees rated Mahler is bit cheaper then 80 degrees rated. Is the temp rating of the thermostat a material factor here?
Mike W.
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Re: diagnosing and fixing aux fan... or more?

Post by Mike W. »

Mashford wrote: Mar 19, 2023 10:22 PM Also, I am trying to figure out the differences between the temperature ratings of the different thermostats available for my 535is M30 configuration. The 71 degrees rated Mahler is bit cheaper then 80 degrees rated. Is the temp rating of the thermostat a material factor here?
80C is what they came with and what the FI is based on. It's a fallacy that using a lower temp stat will help with overheating. If it's anywhere near overheating either a 71 or 80 is long since wide open. A 71 will have it running cooler when it's cool and doesn't matter, but will not help prevent overheating. It's not a big deal, but I would go with the 80.
Could this be related to heater core, then, contrary to having ruled that out before?
No, you could block off or bypass the heater core and it won't do anything related to overheating. Well, except sort of one thing. Running the heater when it's running hot or near overheating will help dissipate a little bit of heat, but not enough to really make any difference. Turning it on at first will lower the temp very briefly, but then it returns to where it was. Heater is a non issue.

The hot/cold thing is very odd, and speaks to low coolant. Take that little hose off that goes to the reservoir and make sure the nipple isn't collapsed. There's supposed to be a little brass bushing in there and if missing you can crank down on the hose clamp enough to shut off flow.
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Mar 19, 2023 10:16 PM ... the cabin heater started blowing cold, then hot, then cold again and finally back to hot.

Could this be related to heater core, then, contrary to having ruled that out before?
Not the heater core, but the heater control valve. Aside from ensuring you bleed the air out of the heater circuit, you can eliminate this as a variable. Just don't mess with it or be concerned about it for now -- it's a red herring.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Thanks, fellas. New thermostat is on the way and hope to install this weekend, if not sooner.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Reasons for optimism: installed the new thermostat last night and drove for 20 minutes or so. Gauge went to vertical and held there for a while, and then dropped back down to below vertical (!!) and stayed there for rest of test drive. Cabin heat remained constant. Parked the car with no overheating. I will take it for a longer drive today/tomorrow.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Mashford wrote: Mar 24, 2023 1:07 PM Reasons for optimism: installed the new thermostat last night and drove for 20 minutes or so. Gauge went to vertical and held there for a while, and then dropped back down to below vertical (!!) and stayed there for rest of test drive. Cabin heat remained constant. Parked the car with no overheating. I will take it for a longer drive today/tomorrow.
Just drove for 40 minutes stop and go traffic and gauge stayed below vertical. I will do a highway test drive later today, but I am calling it fixed now.

It was the thermostat.

I am happy to have a new radiator and main hose, anyway, and to have gotten under the car to check things out. I think I will turn my attention to cosmetic tasks now.

Thanks again for all the help everyone! I am soooo grateful for this forum!
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Mar 25, 2023 12:35 PM It was the thermostat.
We should have suspected it all along, but for some reason, none of us emphasized it -- it's a "start at zero" item. A stovetop test is something that we should mandate going forward.
Mashford wrote: Mar 25, 2023 12:35 PM Thanks again for all the help everyone! I am soooo grateful for this forum!
You're welcome, and thank you for the appreciation. This thread has added to the knowledge, so it's a part of getting things corrected.
Mike W.
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Re: diagnosing and fixing aux fan... or more?

Post by Mike W. »

Mashford wrote: Mar 25, 2023 12:35 PM

Just drove for 40 minutes stop and go traffic and gauge stayed below vertical. I will do a highway test drive later today, but I am calling it fixed now.

It was the thermostat.
I feel I owe you an apology. I'm sorry. So simple and yet I didn't suspect it. I should have seen it coming. :brick:
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

All good, Shawn & Mike! It was fun and ended well.
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