Hey @Whisky B

Purchased my R53 three years ago, did a complete overhaul of the cooling system. Upgraded thermostat housing to aluminum, new thermostat, upgraded expansion tank to aluminum, new heater core, new water pump (bmw oem), new rad, new fans... everything cooling was serviced or replaced. Not even 1500km later coolant vanishing, eventually found coolant leaking down the front of the engine under the water pump. Removed the water pump to find it leaking from the weep hole, replaced it with another OEM BMW pump, replaced the flange and block seal at the same time. 1500km later, more vanishing coolant, took it back apart and repeated the above to find leaking coolant from the weep hole on the water pump again.

It was at this point i stopped, and read into coolant as it was my only take on what was going wrong. I was using generic Prestone coolant, as i do with every other vehicle i have or had. Apparently BMW is rather specific on coolant as taken from another forum " BMW's are sensitive to the type of coolant used due to the variety of metals employed in the engine. It should be phosphate- and silicate-free "

Went through the replacement process again, and now have over 4000km with Zerex G-48 coolant and have not lost a drop. Now this is all my first hand experience combined with forum knowledge. To know if its leaking from the weep hole itself is rather hard to diagnose, basically have a coolant sludge leaking down the front of the engine and you'll notice coolant on the front of your oil pan.

 

sounds crazy, but "phosphate and silicate-free" coolants are considered Inorganic Organic Technology (IOT) that apparently protect older engines from corrosion. I assume this means oxidization or rust, but not weep holes on MINI water pumps. I must have a "BMW safe" version of the green stuff, as much as I've been crawling around under there, I haven't spotted any leaking coolant. Of course now I'll have to pull the bottle and read the label just for peace of mind. Thanks for sharing I was absolutely clueless as to how detrimental the wrong coolant could be, probably why my pump failed.

 

The shaft seal is tricky, it's usually just a carbon disk against another carbon disk. Some types of coolant can get a little abrasive and cause the seal to abrade itself and leak.

Silicates can be bad for this. Some seals are engineered to resist this, apparently the BMW specified seals do not.

 

I’ve serviced three superchargers and all three were just like in your pictures of the waterpump side , low on oil with no visible leaks…