[SOLVED] New OEM BMW radiator causing overheating issues?

[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.

[austin_caccavo]

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

That's correct, but the new Genuine BMW radiators now have metal tanks (same part number) and no longer come with the plastic tanks hence the issues in my original post.

[milarsky]

Ah, yes, now I see. I thought you were comparing an aftermarket all-aluminum rad.

[ahab]

S38s are supposed to idle at 850 +/- 50. Looks like you're down around 600. Maybe you're moving less fluid through the radiator?? It may not make a lot of difference but it certainly isn't helping.

Is this the high compression engine with the WAR chip?

[austin_caccavo]

S38s are supposed to idle at 850 +/- 50. Looks like you're down around 600. Maybe you're moving less fluid through the radiator?? It may not make a lot of difference but it certainly isn't helping.

Is this the high compression engine with the WAR chip?

I understand your point, but it works great with the plastic radiator so I don't think that makes enough difference to matter. And yes, 3.6 10.5:1 Paul Burke build.

[ahab]

Good point. Your dad sent me the same tune for my 11:1 engine and it runs like a banshee. My idle is about 1k +/- 50 depending on temp. Did you drop the idle speed?

[austin8753]

now that i've fixed my air conditioning (!!!!!!!!!!!!), i'm running into literally the exact same issue you've been dealing with. guess it's time to find a used radiator............

[austin_caccavo]

Good point. Your dad sent me the same tune for my 11:1 engine and it runs like a banshee. My idle is about 1k +/- 50 depending on temp. Did you drop the idle speed?

Right on! We've done a bit of fine tuning over the years so it's likely a little different than what you currently have, but still fast!

now that i've fixed my air conditioning (!!!!!!!!!!!!), i'm running into literally the exact same issue you've been dealing with. guess it's time to find a used radiator............

Haha! With the OEM Bosch stuff too... that's interesting to hear.

[cgraff]

Hi everyone,

So to add this thread.

1. euro vs US radiator difference is due to the temp sensor ports for the aux fan. US uses a dual switch vs euro that uses two switches.

2. The M5 radiator isn’t an efficient cross flow radiator. If you look, the location of the hoses is not perfectly diagonal, like a 535 rad. On one side it’s about halfway. This means that at low volume flow, there isn’t enough pressure from the water pump to flow throughout the entire rad. This means at idle, you’re not getting full efficiency. I let my car heat soak on a hot day at idle and temped the rad across and up/down and you can see the relative temperatures support this observation.

3. Fan clutch lock up is at 86 deg C (per spec) for the clutch ending in 918. It’s the lowest temp fan clutch you can buy.

4. I retrofitted a later style (E30) curved blade aux fan which has some improved efficiency over the stock 5 blade.

5. I also retrofitted on my euro the 82/91 aux fan switches over the stock 91/99. You can use a 80/88 dual switch from a E36 318 for the US M5.

6. All this to say that I am improving the airflow across the rad if temps get to the 80 deg C range, so as to get more cooling efficiency at idle in very warm conditions.

7. I also use a 71 deg Tstat vs 80 deg Tstat, which has also improved cooling.

8. My radiator is a new BMW sourced one from 2020. Never had an initial issue with it - so maybe there has been a production problem on more recent ones?

Results:

Temp gauge is normally between 11 and 11:30 in 95% pf operating conditions, while moving. This includes 95 deg F ambient air temps in humid NJ; direct sunlight in summer; hot tarmac. Even in those conditions, if I am idling and sitting at a standstill in traffic, (OBC over 100), and basically heat soaking the car, temp gauge does not go over 12:00.

Not that an otherwise stock M5 (had one years ago) woth new componenta is normal to get to 12:30 or even 1:00 on the gauge in those conditions.

-Chris

[MannyE]

cgraff wrote: I retrofitted a later style (E30) curved blade aux fan which has some improved efficiency over the stock 5 blade.

[cgraff]

cgraff wrote: I retrofitted a later style (E30) curved blade aux fan which has some improved efficiency over the stock 5 blade.

I always thought the M5 stock radiator fan has 9 blades.

I said aux fan. Not main rad fan.

[Mike W.]

Chris, good to see you chime in, I haven't seen anything from you in a while and your input is always interesting.

But from a distance, key to me, seems to be the new metal tank radiator the OP was using. Not that metal tanks are a bad thing, my understanding is they actually provide a bit more cooling than the plastic tanked ones just due to metal being a better conductor of heat, but was your radiator from 2020 metal or plastic tanked? The simplistic and perhaps, or not answer, is the new design, which may very well be more than just tanks, is a lesser radiator.

[gadget73]

would be interesting to pop the original and the new side tanks off to see what the internal config looks like. Could probably even just stick a bore scope in there to see whats going on, but its possible the original has some baffles in there to force coolant flow across the entire core rather than just in the middle.

[johne]

This is very late, but when I had my M5 I replaced my radiator with a factory unit. That one and 3 more factory units failed over the course of 3 years or so. Each one leaking at the bottom right. The fourth was just out of warranty. I ordered an all aluminum one from Wizard Cooling in NY. Perfect fitment. No issues. Currently selling for $559. FWIW.
John

[Machtig]

This is very late, but when I had my M5 I replaced my radiator with a factory unit. That one and 3 more factory units failed over the course of 3 years or so. Each one leaking at the bottom right. The fourth was just out of warranty. I ordered an all aluminum one from Wizard Cooling in NY. Perfect fitment. No issues. Currently selling for $559. FWIW.
John

For clarification, is this radiator from Wizard Cooling the OEM one with aluminum tanks discussed in this thread or an aftermarket one made by this shop?

[johne]

This was an all aluminum radiator. Beautiful workmanship.
John