Hi everyone,
2004 R50 with 270k miles.

I initially noticed a leak with my water pump early this spring, so that was replaced, along with all the gaskets. I also did a coolant flush and replaced with the factory blue coolant, bleeding at both points.

Several weeks later while waiting for my turn in a drive thru, the coolant temperature spiked to almost max. The high speed fan turned on at that point. Some coolant bubbled out. I waited for the car to cool down and it was fine for the drive home. I didn't have any problems with the coolant temp as I was driving it.

I figured that maybe it couldn't regulate the temp so I replaced the thermostat, flushed and bled with new coolant again. Still occasional coolant temp spikes when the car is stopped and idling.

I have noticed the low fan speed never turns on anymore, so I just replaced the fan tonight (I initially tried replacing just the resistor but the two Dorman kits I purchased were broken prior to installing)

Did an idle test with the heater turned to HI. The car ran fine with the low speed fan and high speed fan turning on when it needed to for approximately 15 minutes, but then the coolant temp spiked up again to the same point as all of the previous times. I never felt any heat coming out of the vents inside the car. I felt the upper radiator hose but it was cold. No coolant spilled out because I stopped the car before that happened.

I'm at a loss of what to do now. A little searching I found there might be a coolant valve of some kind in some BMWs and Minis but I couldn't find any reference for one in my Bentley Manual or on RealOEM.com.

I saw some posts regarding the heater core being clogged and leaking but mine is not leaking or exhibiting any of major issues - other than my heat does not work. I did read in several places that a heater core issue will not cause the car to overheat.

Any ideas what to check next?

 

Just did our heater core due to it being plugged. I never noticed a temp spike but had very LTD heat and coolant occasionally was being pushed out of the expansion tank, more than likely due to loss of flow through the core. I can report after the replacing the core we have a lot of good heat and no more coolant coming out of the surge tank. I cut open the old core and it was quite odiously plugged. One thing I did while bleeding the system was squeeze the upper rad hose 10 or so times while running thermostat open to aid in the removal of any air locks. No coolant valve exists that I'm aware of. Just pump and thermostat. If you remove the side panel by the accelerator you will see the heater core and related pipes. If one is hot and the other cold good chance you will be doing the core. Fairly easy job. I found a suitable pan removed the accelerator pedal and punched a small hole in the bottom of the core for a controlled drain rather than soaking the carpets and smelling coolant for the next year or so. Hope that helps and keep us updated.

 

I had some time so I thought I would cut it open. And here's what I found.