I've developed a minor coolant leak and, of course, it's been impossible to find in the jumble that is the engine compartment on my R53. I rented a radiator pressure tester from O'Reilly's but it did not come with a fitting for the Mini coolant recovery tank so it was useless. Has anyone found a viable pressure tester and, if so, did you buy it or were you able to source/rent it from an auto parts store? Thanks.

 

Why not just skip testing the tank. Jury rig something to attach the hose to the expansion tank. You can then test the tank separately with the hose again.

 

Wish I could. The radiator pressure tester is meant for a Stant-type cap. Because the Mini recovery tank inlet is threaded, there is no way to install it and ensure it's air tight. The coolant tank is not the source of the leak. The tester puts the entire system, including the radiator, under pressure. With the myriad number of t- and x-section connectors and small hoses that are part of the cooling/heating system, the leak could be anywhere. Because it's a closed system, once under pressure, the leak will be visible.

 

There’s no clue as to where the leak is?
Under radiator, thermostat, heater core?

Where specifically are you finding the leaked coolant?

 

On the garage floor. Unfortunately, the leak appears to be distributing off other components and doesn't appear on the floor in the same location.

 

If you can sacrifice a spare plastic expansion tank cap, you could drill a 1/2" hole in the top, put in a correctly-sized rubber grommet (found at a hardware store), and use an air-gun with a rubber tip like I have pictured below. Set the regulator on your air compressor to 15psi (cap is rated to 18psi before venting), press the air-gun tip into the grommet (pressing in firmly as to not leak air), release air into tank, then watch/listen for leaks.

Perform this on a cold engine.