Mainly just like that but it was a large leak and made a big puddle in about an hour. I made a “temporary“ fix using Teflon tape in January 2018. I bought a pack O-rings to fix it proper and never had to use it. You can do fix without draining any coolant if you do it fast enough. I lost navy one cup of coolant

?-?

How good is your fluid system.
Mine has always disappeared coolant here and there...
All hoses relaced. Valley Pan. The cover plate by the bellhousing....
She still tends to disappear some coolant now and then. Just topped off 12oz while I have the hood open the other day

I don't recall ever having to do more than safely jack it up and start from the bottom with a bright narrow flashlight beam and trace the coolant leak up to the source. A leak showing on drivers side could be a coolant hose.

After you shut off the engine from operating temp the coolant temp increases as does the pressure. That likely why you are not seeing a leak all the time.

Most auto parts stores will rent a pressure tester and return the amount of the rental fee when the tester is returned.

I have recently had to source a non obvious coolant leak on my facelift 3.0d. It turned out to be a tiny crack in the plastic return pipe on the neck of the second bleed screw. so it would only leak under pressure. I have sourced a replacement pipe but I managed to stop the leak by using a hose clamp on the neck of the bleed screw which seems to be doing the job until I can get time to change the pipe

Found my leak. I caught it in the act. Coming from bottom of the expansion tank and the expansion tank connector (17111438820).

Doubt it is O ring on the expansion tank because less than 2 years old. Will have to take apart to see if expansion tank connector is cracked.

And I am back with the same problem... update:

So i ended up deciding to replace the following for an unrelated reason:
Upper hose, lower hose, aux fan swithc, radiator, radiator mounting plate, expansion tank, coolant level sensor, Trans oil cooler thermo stat, expansion tank connector.

Now 3 days later I am having the same problem as originally.

How hard is it to use that coolant pressure tester?

Did you swap the two coolant pipes? The Harbor Freight kit works. I bought a kit to find a leak on mine. The BMW adapter worked. I found the leak easily. The small upper tank connection was cracked at the o ring. The plastic groove holding the o ring broke.

I've only seen it used once but it seems super easy :)

Really simple

Install BMW adapter on filler neck of expansion tank, Attach pressure line from hand pump.
Pressurize to PSI as marked on gauge (NOT until it blows)

Let it sit and look for leaks

Skill level 1