Cooling troubleshooting in a 2011 E9x (E93) M3:
It took me several days to sort out this seemingly simple issue. I'm happy to say it is finally solved!
Last August I started getting increased oil temperatures in hot weather whenever the A/C was on. This progressed to increased temperatures (yellow warning) whenever I drove in hot weather. Running the heat helped. Shutting the A/C off helped. Increased airflow (moving versus idling) helped to a degree. Classic water pump/thermostat, so I replaced both and refilled coolant. I then followed the bleeding procedure (run engine, open bleeder, let the bubbles out), but continued to have basically the same problem.
Long story short, the "self-bleeding" system kind of sucks and there was still a large amount of air in the system, which just didn't want to bleed. There are a lot of other possibilities I explored, however, so I wanted to put the whole troubleshooting process into a single thread.
Inspection first. Is the coolant level OK? Is there fluid under the car? Do you have broken fan blades? Is the rad full of leaves, squirrels, etc? Is your undertray broken with pieces in the way of airflow? Do you have any missing or broken belts/pulleys?
With that out of the way, connect Protool or other diagnostic that will give you "motor temperature" (coolant temperature) and oil temperature or use the "secret menu" on the dash to get coolant temps. Run the engine at idle (with A/C on and possibly light revs if you need to to recreate the high temperatures) and observe. The following SHOULD be happening:
Coolant Thermostat/WP:
At a coolant temperature of around 80C the COOLANT thermostat should open. You should see coolant temperature quickly increasing (over a just a couple minutes) from ambient up to around 80C and then slowing down dramatically or levelling off when the thermostat opens. You can also check to see if the radiator return hose is getting hot, which tells you coolant is being directed through the radiator. If the hose doesn't heat up, the thermostat probably isn't working. Other possibilities include air in your system (if recently refilled) or a failing water pump.
Oil thermostat:
At oil temperatures around 90C, the OIL thermostat should open. Oil temperatures should level off around 90-100C. The oil cooler (smaller cooler, in front of the rad below the front bumper) should be cold up until that point and then start heating up quickly as near-boiling-hot oil starts running through it. If it doesn't heat up, the oil thermostat can be stuck closed. I found a few forum threads where this was the problem. The oil cooler heating up thankfully rules this out. This repair involves a little more disassembly, and the part is expensive as the oil thermostat is part of the oil filter housing and NOT sold separately. A few websites erroneously list the TRANSMISSION oil thermostat (separate cooling system entirely) as the engine oil thermostat. Different parts. Different cooling circuits. Don't be fooled.
Radiator fan:
At coolant temperatures in and around 90C the rad fan should activate. It will be running at full-tilt by the time coolant temps reach 100 degrees. If you're seeing a big voltage drop, the fan may not be getting enough power and RPM may be too low as a result. Consider alternator/battery at that point, or the fan its self failing.
If the fan isn't coming on at all, it could be the fan has failed. It could also be the (much cheaper) coolant temperature sensor. If the thermostat is OK, as above, you'll see the rate of coolant temperature increase from this sensor level off right around 80C, which is a good "sanity check" for the sensor output. If it's reporting something else (high, low, or any unchanging value) it might be busted. This is a very easy fix, located on the thermostat housing.
If the sensor reports correctly, but the fan is only coming on when the AC is run, after a temperature warning, or when activated in by diagnostic software, there could be issues with the fan controller, under the floor on the passenger side. I only saw this mentioned in one thread, so I doubt it's very common.
Air in the system - "Self-bleeding" is a lie:
If you've replaced parts or refilled coolant, this is a likely explanation. I pulled my hair out for 2 days bleeding via the bleeder screw per official instructions and running in the garage with the coolant reservoir open to no avail. Squeezing the rad hoses while running resulted in burnt fingers and a few bubbles but no real success. It seems the self-bleeding lines empty into the expansion tank above the max fill level, making very large bubbles hard to clear effectively. You can squeeze them out, but the air comes right back in the same way it left.
What worked for me was attaching a no-spill funnel to the coolant reservoir and filling a few inches above the top of the reservoir like you would with cars that fill at the radiator. This placed all of the self-bleeding lines underwater, so when I squeezed and released the hose it wasn't able to pull any air back in. Running the engine and squeezing the rad return hose by-hand (with gloves!) finally cleared several large bubbles, and the car no longer overheats. I squeezed a hose and plugged the funnel before removing to prevent overflow, and then siphoned the coolant back down to "max". The last step is important to avoid risk of over-pressurizing the system.
I hope this helps someone else quickly troubleshoot an unreasonably warm E9x M3. Please feel free to chime in with additional suggestions/corrections.
It took me several days to sort out this seemingly simple issue. I'm happy to say it is finally solved!
Last August I started getting increased oil temperatures in hot weather whenever the A/C was on. This progressed to increased temperatures (yellow warning) whenever I drove in hot weather. Running the heat helped. Shutting the A/C off helped. Increased airflow (moving versus idling) helped to a degree. Classic water pump/thermostat, so I replaced both and refilled coolant. I then followed the bleeding procedure (run engine, open bleeder, let the bubbles out), but continued to have basically the same problem.
Long story short, the "self-bleeding" system kind of sucks and there was still a large amount of air in the system, which just didn't want to bleed. There are a lot of other possibilities I explored, however, so I wanted to put the whole troubleshooting process into a single thread.
Inspection first. Is the coolant level OK? Is there fluid under the car? Do you have broken fan blades? Is the rad full of leaves, squirrels, etc? Is your undertray broken with pieces in the way of airflow? Do you have any missing or broken belts/pulleys?
With that out of the way, connect Protool or other diagnostic that will give you "motor temperature" (coolant temperature) and oil temperature or use the "secret menu" on the dash to get coolant temps. Run the engine at idle (with A/C on and possibly light revs if you need to to recreate the high temperatures) and observe. The following SHOULD be happening:
Coolant Thermostat/WP:
At a coolant temperature of around 80C the COOLANT thermostat should open. You should see coolant temperature quickly increasing (over a just a couple minutes) from ambient up to around 80C and then slowing down dramatically or levelling off when the thermostat opens. You can also check to see if the radiator return hose is getting hot, which tells you coolant is being directed through the radiator. If the hose doesn't heat up, the thermostat probably isn't working. Other possibilities include air in your system (if recently refilled) or a failing water pump.
Oil thermostat:
At oil temperatures around 90C, the OIL thermostat should open. Oil temperatures should level off around 90-100C. The oil cooler (smaller cooler, in front of the rad below the front bumper) should be cold up until that point and then start heating up quickly as near-boiling-hot oil starts running through it. If it doesn't heat up, the oil thermostat can be stuck closed. I found a few forum threads where this was the problem. The oil cooler heating up thankfully rules this out. This repair involves a little more disassembly, and the part is expensive as the oil thermostat is part of the oil filter housing and NOT sold separately. A few websites erroneously list the TRANSMISSION oil thermostat (separate cooling system entirely) as the engine oil thermostat. Different parts. Different cooling circuits. Don't be fooled.
Radiator fan:
At coolant temperatures in and around 90C the rad fan should activate. It will be running at full-tilt by the time coolant temps reach 100 degrees. If you're seeing a big voltage drop, the fan may not be getting enough power and RPM may be too low as a result. Consider alternator/battery at that point, or the fan its self failing.
If the fan isn't coming on at all, it could be the fan has failed. It could also be the (much cheaper) coolant temperature sensor. If the thermostat is OK, as above, you'll see the rate of coolant temperature increase from this sensor level off right around 80C, which is a good "sanity check" for the sensor output. If it's reporting something else (high, low, or any unchanging value) it might be busted. This is a very easy fix, located on the thermostat housing.
If the sensor reports correctly, but the fan is only coming on when the AC is run, after a temperature warning, or when activated in by diagnostic software, there could be issues with the fan controller, under the floor on the passenger side. I only saw this mentioned in one thread, so I doubt it's very common.
Air in the system - "Self-bleeding" is a lie:
If you've replaced parts or refilled coolant, this is a likely explanation. I pulled my hair out for 2 days bleeding via the bleeder screw per official instructions and running in the garage with the coolant reservoir open to no avail. Squeezing the rad hoses while running resulted in burnt fingers and a few bubbles but no real success. It seems the self-bleeding lines empty into the expansion tank above the max fill level, making very large bubbles hard to clear effectively. You can squeeze them out, but the air comes right back in the same way it left.
What worked for me was attaching a no-spill funnel to the coolant reservoir and filling a few inches above the top of the reservoir like you would with cars that fill at the radiator. This placed all of the self-bleeding lines underwater, so when I squeezed and released the hose it wasn't able to pull any air back in. Running the engine and squeezing the rad return hose by-hand (with gloves!) finally cleared several large bubbles, and the car no longer overheats. I squeezed a hose and plugged the funnel before removing to prevent overflow, and then siphoned the coolant back down to "max". The last step is important to avoid risk of over-pressurizing the system.
I hope this helps someone else quickly troubleshoot an unreasonably warm E9x M3. Please feel free to chime in with additional suggestions/corrections.
