So a while back my coolant reservoir decided to explode on the highway resulting in the car overheating. I replaced the reservoir as well as the thermostat. I've been chasing a coolant leak ever since. Theres obvious coolant coming from the thermostat housing that I'm attributing to me using poor parts (I never could get the gasket to fit 100% properly in the housing) and or not replacing a cracked/warped thermostat housing. When looking at it, I also noticed coolant residue on the front side of the block. I figured it could also be where the water pump meets the block. I ordered a fresh thermostat, housing, water pump, and block/pump flange since theyre all relative cheap (250 bucks for all gen bmw parts). Here's the conundrum. I'm currently sitting in front of the car with all the tubing going into/out of the water pump removed and I cant find the coolant leak I expected to be there. The million dollar question: leave the existing water pump be, let the current seals stay sealed, replace the thermostat, see what happens, and potentially have to do this again. Or replace everything, hope it works, potentially get a poor seal, and potentially introduce a leak that didnt already exist.

 

I replaced my WP a few years ago. Have had an intermittent leak from the WP area ever since, getting worse lately. I just nailed down that it's from where the WP inserts into the flange. And very intermittent. I don't understand why...but maybe that's your problem?

 

So I have the flange piece on hand as well. I just cant seem to find any coolant anywhere around the water pump. Now, the front of my block has seen better days thanks to the valve cover gasket and CPS oring leaking for most of the cars life, theyve since been fixed, so it's possible that any coolant is just significantly harder to see than it would be on the bare metal. I just don't know that I want to go messing with something that appears to be ok.