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MINI Cooper Coolant Leak, Thermostat to Water Pump Pipe, R55, R56, R57

September 8, 2017

Dear Otto,
I have a coolant leak that I can’t seem to find the source of.  Over the past few weeks, I have had to add a pint, or so, of coolant once in a while.  Lately, this has become a daily ordeal.  I noticed a puddle under the car, for the first time, a week ago.  It was on the passenger side, just inboard of the wheel.  I can’t see anything at all from above.  I have looked from under the car and the coolant is dripping off the engine subframe and the control arm.  I can’t really see much up there, but the water pump does not seem to be leaking …. it’s dry between the pump and the pulley.  Any idea where this leak may be coming from?  Thanks, Mike


We are at a disadvantage in not having the car in-hand to inspect it, but we do have a thought on the source of your coolant leak.  The R55/56/57/59 MINI models (Cooper, Clubman, Convertible and Roadster – in base, S and JCW) use engine variants that have a plastic coolant transfer pipe that runs from the thermostat (on the left side of the engine) to the water pump housing (right side of engine), along the rear of the engine, under the intake manifold.  This pipe commonly starts to leak at the point where it seats into the “back” of the water pump mounting housing.  Either the o-ring starts to leak or the end of the plastic pipe starts to crack apart.  Leakage is also a common problem after the thermostat has been replaced, as the pipe’s o-ring seal has been disturbed during the thermostat replacement.


Coolant tube removed. Note damaged flange for the sealing o-ring , where pipe mounts into back of water pump housing.

Coolant tube connection port on back of water pump housing.


While the pipe itself is rather easy to replace, the access to the pipe is a bit more work.  The intake manifold and the thermostat must be removed in order to access and remove the coolant pipe.  This is a bit tedious, but not especially difficult.  A moderate DIYer (with a Bentley Publishers repair manual) can have the pipe removed in about 2 hours.  Of course, this is a good time to preemptively replace the thermostat and any crankcase ventilation and vacuum hoses that look dry and/or cracked.  Additionally, new intake manifold seals (gaskets) will be needed and a thermostat gasket (if the thermostat is not being replaced).

Intake manifold, thermostat (at left) removed, coolant pipe (center) removed. It really does look worse than it is!

Finally, if you are considering some performance gains for your turbocharged S model, The FTP turbo charge pipe upgrade kit which eliminates the muffler in the turbo to intercooler piping and the “sound maker” in the intercooler to throttle body piping, is a great upgrade and you will have the piping to the throttle body already disassembled … and the access to the turbo to intercooler piping will be clear as well.  Even if you just install the piping to the throttle body that eliminates the “noise maker”, and install the turbo to intercooler piping later, this is a good time to make the purchase and the perform the partial install.

FTP charge pipe set for N14 & N18 MINI S and JCW R56, R55, R57 etc.

 Click image below for Coolant pipe:

Click image below for Thermostats:

 Click image below for intake manifold gaskets:

Bavarian Autosport

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