[SOLVED] New OEM BMW radiator causing overheating issues?

[austin_caccavo]

Sup mye28! I'm usually just a lurker here, but wanted to pick your brain(s) on a strange overheating issue I've been having on my M5.

TL;DR: After replacing nearly the entire cooling system, the car still climbs to 2 o'clock at idle and struggles to maintain a 12 o'clock position on 90F+ days. Is it possible the new OEM BMW metal radiators are defective? EDIT - August 6, 2023: Somehow, yes...

I have never once had cooling issues, and the car always ran around 11 o'clock (even the hottest of days); however, earlier this year I drove the car to lunch (60F ambient temp/5min drive), and when I came back into the garage and turned it off, the OEM BMW plastic radiator had cracked clean off at the upper radiator hose. As strange as it was, I chalked it up to old age as it was likely 10 years old.

I quickly ordered a new, OEM BMW radiator (which arrived w/ metal tanks in a BMW box), refilled it the system, and after a short 30min drive, was hit with a 1 o'clock temp gauge on a 60F day. Now that it's 90F+, the car is nearing the 2 o'clock range at idle while measuring around 215F at the upper radiator hose. Since the original incident, I have replaced/serviced the following parts (along with other unrelated items) without any luck in improving the situation...

4/02/23 (381,000) - OEM BMW radiator (17112226018)
4/02/23 (381,000) - Coolant flush using OEM BMW coolant (50/50)
4/10/23 (381,000) - Meyle fan clutch (11521466000)
4/20/23 (381,500) - Sachs fan clutch (11521723918)
5/21/23 (382,000) - OEM BMW 80deg (used) thermostat w/ seal (removed a Calorstat unit with 20k miles, tested both units, successful results)
5/21/23 (382,000) - Coolant flush using OEM BMW coolant (50/50)
6/01/23 (382,400) - VEMO radiator fan switch (61318361787)
6/01/23 (382,400) - VEMO radiator fan switch (61311378073)
6/15/23 (384,000) - VEMO coolant temp sensor (13621709967)
6/15/23 (384,000) - FAE coolant temp sender (62161360870)
7/03/23 (384,100) - A/C Solutions (CSF) high flow parallel flow condenser w/ 13" SPAL pusher fan (ACS-x)
7/03/23 (384,100) - Performed Bentley OHM values on coolant temp sender (successful results)
7/03/23 (384,100) - Removed cluster and cleaned and checked temp gauge for cracks/etc. (successful results)
7/17/23 (384,250) - Hepu 535i pump (11519070761) (removed an OEM BMW unit w/ no signs of failure)
7/17/23 (384,250) - OEM BMW radiator (again) (17112226018)
7/17/23 (384,250) - Coolant flush using OEM BMW coolant (60/40 water/coolant)
7/30/23 (384,500) - Performed head gasket combustion gas test (successful results)
[EDIT - August 6, 2023] → SOLVED
8/04/23 (384,600) - Installed a used (plastic) OEM BMW BEHR radiator (17112226018) with BMW coolant (60/40 water/coolant)

Additional notes: This is a 3.6L Paul Burke stroker w/ that I've put about 90k miles in the past 6 years. I have experienced zero coolant loss over the duration of my ownership, and the expansion tank, cap, level sensor, and all hoses have been replaced with OEM BMW parts over the last 5-10 years.

Thanks in advance!

[turbodan]

Does the cooling system overpressurise? If you let it sit overnight does it still have pressure in it after cooling off?

[Mike W.]

Is this a M30 car or a S38 car. If M30 there's been some discussion about the SA radiators with round tubes not cooling well. If S38 IDK what the options are. Check out this thread. viewtopic.php?t=154621

[austin_caccavo]

Does the cooling system overpressurise? If you let it sit overnight does it still have pressure in it after cooling off?

I just pulled the cap off after about 3hrs, and it didn't seem to have a ton of pressure in it. No excessive pressure overnight.

Is this a M30 car or a S38 car. If M30 there's been some discussion about the SA radiators with round tubes not cooling well. If S38 IDK what the options are. Check out this thread. viewtopic.php?t=154621

88 M5 (S38), so unfortunately there are only a few options. I'm reluctant to go to an aftermarket radiator unless I need to, but would much prefer a NOS plastic OEM M5 radiator to rule out the new metal ones from potentially being defective.

[Mike W.]

88 M5 (S38), so unfortunately there are only a few options. I'm reluctant to go to an aftermarket radiator unless I need to, but would much prefer a NOS plastic OEM M5 radiator to rule out the new metal ones from potentially being defective.

Ok, now this is an absolutely crazy thought, but since you're kind of in a spot and it has metal tanks, what about a recore? Not many do it anymore, but I see you're in Sac so there ought to be someone over there that still does it. I didn't have them done myself, but I've had a couple that came in cars I bought and they always performed well.

[austin_caccavo]

Ok, now this is an absolutely crazy thought, but since you're kind of in a spot and it has metal tanks, what about a recore?

Not totally crazy - I've thought about it...

[austin_caccavo]

After doing some research on RealOEM, I noticed the euro M5 uses a different part number (17112226082) than that of the US M5 (17112226018). Does anyone know the difference between the two?
(https://www.schmiedmann.com/en/product/ ... -2-226-082)

[turbodan]

It would be easy to verify that the radiator is functioning. Pull the fan and shroud, warm the engine until the thermostat opens and check if the radiator is hot from top to bottom. Cold spots indicate no flow.

Does it overheat when idling or only while running at speed?

[Blue Shadow]

What radiator cap are you using? I read here on my that the ///M motor needs a 1.4Bar cap not the usual 1.0 bar unit in the M30

Don't know if that will change the overheating, though.

[austin_caccavo]

It would be easy to verify that the radiator is functioning. Pull the fan and shroud, warm the engine until the thermostat opens and check if the radiator is hot from top to bottom. Cold spots indicate no flow.

Does it overheat when idling or only while running at speed?

Planning on doing this later today, but since I'm on my 2nd new radiator I'd assume it's "fine", but will report back! It overheats at idle as well as at slow speeds. On the freeway it takes a very long time to cool off and get back down to 12 o'clock.

What radiator cap are you using? I read here on my that the ///M motor needs a 1.4Bar cap not the usual 1.0 bar unit in the M30

Don't know if that will change the overheating, though.

I'm using the 1.4BAR cap, but just ordered a new one (as well as a vacuum bleeder) to rule it out (17112227683).

[austin_caccavo]

Yesterday, I observed the external temps of the upper and lower radiator hoses. Here's the spread as the gauge climbed:

10 o'clock - 155/106
11 o'clock - 180/140
12 o'clock - 185/170
Just past 12 o'clock - 195/180
1 o'clock (as seen in photo) - 200/187

[Rouven036]

I saw that you have replaced twice the viscous fan clutch but it's not the first time that non original clutches face issues with proper function. The viscous fan is engaging clearly audible in my car at around the half or slightly above mark on the gauge.
If this doesn't happen then rectify the issue here first. In idle you need airflow from a proper engaging Fan unit. If that fails you will have always temperature issues. Also keep in mind that the Fan disengages above a certain rpm. Best to test it at around 1500-2000 rpm in idle

[marek]

You might have an air pocket. Did you also replace the thermostat? I highly recommend the vacuum fill. That's what I use on all my cars when changing coolant or doing cooling system work.

[austin_caccavo]

I saw that you have replaced twice the viscous fan clutch but it's not the first time that non original clutches face issues with proper function. The viscous fan is engaging clearly audible in my car at around the half or slightly above mark on the gauge.
If this doesn't happen then rectify the issue here first. In idle you need airflow from a proper engaging Fan unit. If that fails you will have always temperature issues. Also keep in mind that the Fan disengages above a certain rpm. Best to test it at around 1500-2000 rpm in idle

The fan clutch seems to be locking up correctly when it's hot, but perhaps not as much as necessary if there's a cold spot in the radiator (still need to confirm this).

You might have an air pocket. Did you also replace the thermostat? I highly recommend the vacuum fill. That's what I use on all my cars when changing coolant or doing cooling system work.

Yes - the thermostat was replaced several times. The new vacuum fill kit arrives in a few days, so I'll be report back asap!

[austin_caccavo]

Update: I ended up sourcing a used BEHR E28 M5 radiator so I am going to swap that in this weekend and see if that makes a difference and/or proves my theory with the newer radiators being less efficient. Stay tuned.

[41magfan]

Should be a 20 degree difference if i recall correctly. My M5 will idle quite a while in 90 degree temp with no problem wo the aux fan at all fwiw

[Mike W.]

The fan clutch seems to be locking up correctly when it's hot, but perhaps not as much as necessary if there's a cold spot in the radiator (still need to confirm this).

IIRC S38s are a bit more crowded in that neighborhood, but the newspaper test for fan clutches is pretty easy and a good test.

[Blue Shadow]

but the newspaper test

Newspaper? What is that? Where can we find one?

[Mike W.]

but the newspaper test

Newspaper? What is that? Where can we find one?

Yes, an artifact from an earlier era.

[austin_caccavo]

SOLVED! Thanks to Sam (@sam.the.jam), I installed a used (plastic) BEHR M5 radiator on Friday and just got back from a very successful 350mi roundtrip. Outside temps ranged from 75F to 105F, yet the car stayed in it's previous 11-12 o'clock range that I am used to seeing. The highest I saw was during heavy stop and go traffic outside of Davis (105F / OBC displayed 120F+), where the the temp gauge just barely crossed the 12 o'clock mark with the A/C on full blast.

Also, for consistency sake, I kept everything else the same and did the same bleeding process (non vacuum fill) as I had been in the past with the same 60/40 water/coolant mix. Very thankful to say things are back to normal with successful results, but also very disappointed as this proves my theory that the new metal radiators run hotter. I looked through the one I removed, but there's nothing that would lead me to think it wouldn't work... so hopefully BMW can address this issue!

the newspaper test for fan clutches is pretty easy and a good test.

I did the "newspaper test" on all 3 fan clutches and they all seemed okay. After doing it again with the new (used) plastic radiator, it's working perfectly.

[austin8753]

interesting to note. mine also likes to get quite warm when idling, often getting in the 1/2-2/3rds range. as soon as there's airflow, temp comes right down to 1/3 and stays there, until i idle again for more than a few minutes.

new fan clutch installed yesterday made absolutely zero difference. guess these new radiators suck. at $600, that's frustrating...

[Mike W.]

Glad you got it working ok. Just for the record, did the new, expensive, but lacking, radiator have round tubes or conventional flat tubes?

[LeiseyJr]

Glad that fixed it, and it's no longer collecting dust in the shed.

[Rouven036]

Great news!

[austin_caccavo]

Thank you all for your help! Glad to say it's back to normal, but it sucks that the new metal radiators are problematic. If anyone has a NOS/NIB plastic OEM BMW M5 radiator, please let me know - I'd be interested in buying it!

[austin_caccavo]

Glad you got it working ok. Just for the record, did the new, expensive, but lacking, radiator have round tubes or conventional flat tubes?

It had the conventional flat tubing similar to the plastic radiator. After looking at it further, I don't understand how/where things went wrong as it looks promising.

[mottati]

would be interesting to bring to a radiator shop to take it apart and inspect it.

[austin_caccavo]

would be interesting to bring to a radiator shop to take it apart and inspect it.

I thought about that too, but it's already been returned to FCP/BMW...

[austin8753]

makes me wonder if the internal diameter of the tubing is smaller than that of the standard aluminum radiators... thus, causing the issues we have here.

[milarsky]

Hello Austin. I am confused. FCP doesn't seem to sell any radiator other than the stock Genuine BMW 17112226018 for the M5.