So last Friday leaving work (Iowa) no heating during the drive (20 min) enough time for engine to come to temp. Messed around with temp setting from 70 to High and full blower no difference. However, I could smell coolant. Come home, park it walk out and I could hear it a trickle, as well as smell it, some white smoke coming from the hood. check in about 10 min. Sure enough, there is a small puddle underneath at first glance coming right off from tranny on driver side. I am at 88K miles never replaced thermostat, figured it must be the thermostat. Checked the coolant fill bottle and it was almost fully empty. Order it, comes in, it's a new version so needed the adapter for electrical install it. Torque it to specs, make sure all clips and hoses and clamps are on. Follow instructions to blead the system. Go for a ride, heat is back and working really good. The car is not overheating normal temp. Come back to the driveway there is a leak a slow one but leaking.

Next day, go to troubleshoot it seems during my bleed, the PS plastic bleed valve on thermostat crumbled and was not sealing well. Order the replacement bleeder screw, install it, bleed the system again. Dry up everything really good, clean and wash with brake cleaner. Let it come to temp idle, all normal no leak not overheating. Go for a short drive around the neighborhood, get it to 108 Celsius fans kick in and car stay between 98 and 105 Celsius. Park in the driveway, look underneath just a few drops, figure it's normal just something I missed. Park the car, the auxiliary kicks in and I go in. We leave for dinner at hour later and there is a small puddle underneath again.

So today got the coolant pressure tester and tested the system. It would hold steady at 1.1 bar. There was no drop in pressure over the period of 5 minutes. So it's not coming from any of the hoses above the tranny and not thermostat housing, also checked the back plastic pipe that connects the water pump and the thermostat (that C clip was a B to get on) but no leak there. I check for the oil cooler housing and auxiliary pump it's all dry. What am I missing here? When thermostat heats up and opens up does something change and I am unable to get a leak with cold test? I was fur sure it was the auxiliary pump or the oil cooler gasket but it's dry. It still pools on top of the tranny! But pressure test does not show it leaking. What does heat and turning off the car change? I will post pics via my google drive: https://photos.app.goo.gl/2p9vxvPd9fjvPBW49

 

Heat causes expansion so something that is say a crack on that plastic garbage Thermostat housing can open up and leak when it warms up.

 

I mean it's brand new but that doesn't have to mean jack, considering the bleeder screw disintegrated. Off to the store to buy some coolant dye to use with the UV glasses and light.

 

And no dye locally. Gonna have to wait. You would think 20 psi would open it up. I will post am update once I know.

 

So it was the elbow on the coolant fill tank. While I had it tucked away the V clip got moved just a little bit allowing for nipple and rubber o-ring to have a touch of play. Hence heating would expand it and subsequent cooling would shrink it but when shrinking there would be a small gap that allowed coolant for escape. And when driving the wind coming though would spread coolant toward the back of the engine bay. Thanks for Mini-Is_for-me for the comment.

 

Yes, the whole coolant tank is a completely fubar mess. It is like they remembered it had to go in at the last second.

 

Is the leak still on the drivers side?

It's not uncommon for the plastic water piper that goes from the thermostat to a housing near the water pump to leak.

In my case, there is a small leak after I shut the car down.

This will be on the passenger side. You can conform it's the pipe by looking underneath, using a mirror to determine that the leak is from the pipe on the other side of the water pump and not the water pump.

I fear that I replaced my water pump when the actual problem was the water pipe. The Mini service guy that I spoke with refers to it as a crack pipe, because that's what it does.

 

I have the cracked pipe on the Thermostat side. I think the plastic pipe in a METAL engine can pretty much crack on either side. Too many "Einmal Bier, Bitte" for Mini Engineers and original architects.