Coolant Leak at Radiator
 

I've had this small coolant leak for about 2 months now. I thought it was from the trans cooler seals but both of those are new and I just replaced them again anyway. But still leaking..
I'm thinking it's leaking from the radiator mounting plate. Does coolant actually flow through this piece? And how does it seal? I didn't see where I could buy replacement seals for it. It's PN 17111438819.

If you could get a picture of the radiator that might tell you more.

I can't get a pic of the radiator without taking everything apart unfortunately.

Is there a drop-in radiator upgrade I can buy for the M54 engine and auto trans? Like the 4.6 or 4.8 radiator?

I meant get a pic of a replacement rad like you got a pic of the adapter.

Time to do a cooling overhaul (radiator, thermostat etc).
Info in forum.
Brands matter, so do your research.

You could have a cracked tank,like I did...

I just bought a new tank and rebuilt the radiator after it was rodded out.

The crack in mine was on the left side tank about 3" above the outlet tube and it only leaked after shutdown (until it blew out)

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I know I'm probably looking at a cooling overhaul. I already did the thermostat,water pump, hoses, and expansion tank maybe 30k miles ago. So probably will do the other parts now. I'm just curious if this mounting plate can leak or if it seals to the radiator somehow? I guess it must I just don't see how without taking it apart.

Are there any drop in radiator upgrades? As example the Z3 S54 radiator was a bigger direct fit for the e36 M3.

Stock radiator pic

The mounting plate is like it's own tank. Water flow through it is for transmission oil cooling. If you replace it, order a transmission oil thermostat! It will break if you try to remove it. Mine did. The plate is connected to the radiator with another three way flow adapter.

Interesting. I would have said that the mounting plate doesn’t have coolant in it because my N62 doesn’t. It’s also a stupid design for yet another failure point. But on looking at the part, it certainly does look like it has coolant flowing through.

Note: our radiators are aluminum with plastic end caps, like most cars these days. The failure point is on the seam where the plastic connects to the metal. Mine has had a pinhole leak for the last couple of years and I’ve been putting liquid epoxy on the seam as a temp fix. Seems to work ok. I’ll change the radiator in the summer.

My N62 setup:
https://www.realoem.com/bmw/enUS/sho...diagId=17_0291

I had a leak in the same location and bought a replacement radiator from eBay. The repair center that changed the oil pan gasket said I needed a new radiator to fix the leak. I had everything apart and discovered the ebay unit didn't have the hole for the transmission oil cooler.

There is a rubber o-ring that seals the oil cooler to the radiator. The leak was coming from there. I replaced the o-ring with a new one and no leaking since. I installed it in May 2023. Sent the radiator back and got a full refund.

This is the o-ring I got off Amazon. I went with Viton because of chemical and temperature compatibility. I had a butyl o-ring but Viton has a higher temperature rating. Paid $17/5 pcs

M4x38 Viton O-Ring, 75A Durometer, Round, Black, Viton, 38 mm ID, 46 mm OD, 4 mm Width

If you're talking about PN 17101439140, there are 2 of them and I've replaced them twice now. That area is clean, it looks like it's seeping between the radiator and mounting plate. I'm just gonna go ahead and replace the radiator and mounting plate with trans thermostat I guess.

The only thing I can advise is to do a cooling overhaul using ONLY BMW brand when
it comes to the mounting plate, reservoir + cap, hoses x 2.

Tstat: Wahler is good.
Rad: BMW vs Nissens.

Pulleys: INA.

Belts: Conti.

I got everything replaced the other day. Not too bad of a job. I didn't even pull her into the shop. So far no leaks! I couldn't find the smoking gun on the old radiator and mounting bracket but my suspicion is an old/dry o-ring. You can see in that one picture, there is one connection on the radiator and plastic mounting bracket. The bracket has an o-ring inside so technically it could be replaced if you found the right size, then you wouldn't need the $50 mounting bracket.

Parts replaced:
Radiator
Radiator mounting bracket
Coolant fitting
Trans thermostat
Trans cooler seals