Help re: intermittent overheating

[LSB4Me]

Hi Everyone:

I am have been having some strange overheating symptoms and am hoping that you all can identify the part(s) that need changing.

After a decent testing period, I can say that the coolant temp starts to climb: (1) on hot days; (2) with the AC on; and (3) when the motor is being run harder—meaning, shifts at 5k+ or while under load (uphill). Another clue is that the coolant temp returns to the midpoint when turning the AC off. And yes, I can hear the aux fan doing its thing and see it running when I get home before shutoff.

This car is new to me and my records are good, but not great. A challenge here is that my trusty mechanic doesn’t like to “throw parts” at a problem, which is typically my go-to—if it ain’t behaving like it should, replace everything. I still might do this and take the heat from the shop.

With that said, it seems like the cooling system can be broken into two parts: (a) the radiator/fan side; and (b) the water pump side.

Any thoughts or opinions on which of these two is the likely culprit? I would like to start with a targeted approach, if possible.

*Disclaimer: I’ve read all the thread and bought the “easy” sensors. I will install the lower radiator hose sensor this week, but am not optimistic given the above.

Thanks in advance!

[Tbonem3]

Radiator and/or fan clutch. A new radiator alone would solve your issues I bet. So much so that you could remove the fan and still not see over heating.

Please no one say "air". System is self bleeding.

[LSB4Me]

Radiator and/or fan clutch. A new radiator alone would solve your issues I bet. So much so that you could remove the fan and still not see over heating.

Please no one say "air". System is self bleeding.

*heart emoji*

Follow-up detail. When the coolant temp starts rising, the AC seems to lose some of its oomph—both fan speed and temperature. Does that confirm the suspicion of radiator/clutch fan?

If so, I have questions about radiator brands/choices in the next round.

[heinzboehmer]

Please no one say "air". System is self bleeding.

Ah sounds like an issue with air...flow


Yeah your radiator is probably old and filled with debris from the road or has a bunch of bent fins. This won't allow enough air to flow through it and cool the liquid inside it.

If you want to track down the issue before starting to swap out parts, you could remove the radiator shroud, move the AC condenser out of the way and try to blow out any debris that's caught in the fins of both. Make sure to blow it out in the opposite direction that air normally moves (i.e. blow back of the car to front), so that you don't just lodge everything in further. If the issue goes away (or gets better), then a new radiator should take care of it. Otherwise, fan clutch would be the next culprit.

[heinzboehmer]

If so, I have questions about radiator brands/choices in the next round.

Number one choice is stock. Second choice would be stock.

There's been a bunch of threads where people have issues with aftermarket radiators. Resolution is always to be going back to a new stock radiator.

[LSB4Me]

Hah! T-Bone will enjoy the irony there.

I will give some thought to cleaning the radiator but at $300ish, it’s probably best to start fresh as the cooling system is one of the last mechanical components to be baselined. I’ve been through everything else in the last 3 months. Good times.

Copy that. Genuine radiator it is.

Question 1: Does the fan clutch make a noise (a rattle, perhaps) when it’s on the way out?

Question 2: I will replace the hoses with the radiator. Silicone (Mishimoto?) or stock here again?

[oceansize]

Hah! T-Bone will enjoy the irony there.

I will give some thought to cleaning the radiator but at $300ish, it’s probably best to start fresh as the cooling system is one of the last mechanical components to be baselined. I’ve been through everything else in the last 3 months. Good times.

Copy that. Genuine radiator it is.

Question 1: Does the fan clutch make a noise (a rattle, perhaps) when it’s on the way out?

Question 2: I will replace the hoses with the radiator. Silicone (Mishimoto?) or stock here again.

1. Not in my experience. This should be replaced at 100k in my opinion as a wear item.
2. Stock is fine, no need for silicone unless you want to.

3. Get this o-ring kit. This dude is a forum member.

[Tbonem3]

Stock for everything. Factory bmw radiator (Modine build) is surprisingly cheap right now still at $3xx. For hoses, genuine again, but to save $ you could get the cheap OEM REIN, but then replace the junk o-rings with quality ones sold by fellow member here @wofln8tor.
Fan clutch goes bad when the viscous element fails. I believe they work by centrifugal force. So not a noise or bearing thing, just won't have much force to spin. You can roll up a newspaper and stick in there and see if the fan stops.

I would delete the fan simply to avoid it grenading the hoses and hood.

[heinzboehmer]

3. Get this o-ring kit. This dude is a forum member.

Also recommend doing this.

You can get the rein hoses to save a bit of money over the genuine BMW ones. On the now-dead M3forum, there were reports of people having issues with the rein o-rings (the hoses are fine), but if you replace them with the ones from WOLFN8TR, it won't be an issue. That's what I did on my car.

Edit: ah damn tbone beat me to it

[Tbonem3]

[LSB4Me]

Roger that, guys. I had the o-ring guy’s post bookmarked for a later day . . . which seems to be today. I will get those for sure.

Regarding Rein, I’ve used their parts on a prior P-car (as they were the OE supplier and I was in a pinch). I’ll see what the Genuine hoses run and will likely go that route as retracing steps due to inferior parts is a pet peeve of mine. Do it once . . .

ECS has the genuine radiator at $280ish. After LA tax and shipping, it’s $340. Seems reasonable to me.

What’s the time requirement on this job for a seasoned pro?

[Tbonem3]

ECS is charging shipping on that? Look at FCPeuro too.

[heinzboehmer]

Rein makes good stuff. Their hoses are totally fine. Might even be OE for the BMW stuff. It's just the o rings that aren't good enough.

Job would take me 1-2 hours. Probably closer to 2 after I spill a bunch of coolant on the floor and waste a bunch of time cleaning it up. Someone who actually knows what they're doing can probably get it closer to 1.

[jet_dogg]

Hah! T-Bone will enjoy the irony there.

I will give some thought to cleaning the radiator but at $300ish, it’s probably best to start fresh as the cooling system is one of the last mechanical components to be baselined. I’ve been through everything else in the last 3 months. Good times.

Copy that. Genuine radiator it is.

Question 1: Does the fan clutch make a noise (a rattle, perhaps) when it’s on the way out?

Question 2: I will replace the hoses with the radiator. Silicone (Mishimoto?) or stock here again?

Don't buy mishimoto anything.

You never mentioned the mileage.

[LSB4Me]

Don't buy mishimoto anything.

You never mentioned the mileage.

Crossing Mishimoto off the list of good guys. Mileage = 138k . . . hence the urge to fully refresh/baseline.

Based on the advice here, I’m planning to with the radiator, hoses, clutch fan and fan blade. That seems like the front half.