Beware. This is a long-winded request for help. You know Minis? I love my Mini, but I have a problem. I have been trying to fix this for over 6 months. The difficulty is that there is no Mini dealership in Maine! Big state, no help. I'm kinda on my own here. So.....

2010 Mini Cooper R56 Hatchback
n12 engine, normally aspirated.

Problem: Overheating

Symptoms: Misfiring on random cylinders, but mostly #2 after about 10 min of run time. Not as often or quick if I run A/C compressor or, oddly, unplug the coolant temp sensor.
Sometimes goes to limp-home-mode
Transmission gets sloppy
Post-shut down, I can hear the coolant boiling inside engine
Some Coolant is often pumped out onto ground after shutdown.
Once, it overheated so badly, that it dropped a valve seat. Hence the second head job (head gasket, etc).
However
No overheat msg, in fact, no msgs at all until misfire messages. No leaks!

New parts:
Replaced head gasket (twice)
Valve job, etc. New gaskets all around.
New plugs, 3 new coil packs, oil, filter (twice)
New water pump/gaskets/belt
New thermostat and housing, New coolant temp sensor (4 times)
New coolant reservoir cap, new Radiator.
Test results:
Radiator fan will run at high and low speeds.
Radiator fan runs on high when a/c compressor is on
Radiator fan runs on high speed whenever Coolant Temp Sensor is unplugged and continues to run for some time after shutdown.

Notes:
I use the manual bleeding method. I have tried with car level and with front elevated.
Inspection of wiring harness and associated plugs is un-remarkable.

I have been at this for quite some time! My mini still overheats during regular operation. I cannot seem to get in front of it. I think I may have:
1. A bad computer?
2. Incomplete bleeding?
3. Warped head? (Despite two trips to a very reputable machine shop.)
4. Something else?

How do I confirm FLOW?


If you have read this far, thank you!

 

After all the coolant system repairs, are you sure the hoses were all reconnected to their correct location? Real OEM illustrated parts list has some pretty good diagrams --- http://www.realoem.com/bmw/enUS/select Also ensure your hoses are not collapsed, or too soft allowing them to collapse.

Coolant system can be pressure tested to ensure no leaks --- maybe a cracked block or head? No oil in the coolant and no coolant in the oil? Any of the spark plugs "extra" clean, or any other indication of coolant getting into a combustion chamber? Compression or leak-down test results?

 

To oldbrokenwind,

Thank you for the reply. Here we go...

If you boil your coolant, the steam increases the pressure beyond what the system is designed for. This causes the coolant level in the coolant reservoir to rise. If it rises far enough, it overflows. That is the only time the system ever looses fluid, when it boils over.

Hose routing - Check! Honestly, it's hard to mess that up, but I re-checked anyway. All ok.

Hoses - No collapsed.
Leaks - None. Never have been and aren't any now!
Plugs - Forgot to say, all of them are new, also. The old ones were normal in appearance. Replaced 'em anyway.
Oil in coolant - Nope!
Coolant in oil - Nope!
Leak down test - Passed!

The car runs like new! Lots of power. Smooth. Sounds great.....right up until it starts misfiring.

Here is what really chaps me: I have never, not once seen an overheat light on my dash. That is why I keep coming back to:

1. Coolant temp sensor. (Replaced 3 times)
2. Flow (translate - air lock...bad bleed.)
3. Computer?

Rhendy

 

Replace the coolant reservoir bottle and drain the system completely. Only add in the exact capacity shown in the owners manual. When the car is at temp, with the heat on- use the bleeder screw on the thermostat housing only. Let the car sit overnight to
cool. In the AM remove the reservoir cap and top off bottle to 1/2 way.
You’ve done a lot of work!! It’s not supposed to be that heroic.

 

Thanks for the reply...

Well! The coolant reservoir is the ONLY thing left! Why or how would that do it? It is not leaking. What else does it do?

Rhendy

 

If you have an air lock the coolant will never circulate. To check run the engine and open the bleeder on the thermostat housing till water come out instead of steam.

 

Thank you all for your answers and advice.

I finally had the car towed to the nearest, reputable Mini shop. After testing on all of the expensive testers, they vindicated me, somewhat but also gave me bad news.

1. The car does a great compression test and leak down test when it is cold. But when it warms up, the number two cylinder compression drops to almost zero. Since the top end has been done, twice, he says it is probably a piston or the block. Not good, either way.

2. The computer, despite receiving valid signals from all of the sensors fails to activate the radiator cooling fan resulting in overheating. (Probably why the block or piston got cracked.)

The good news is : "Now i know."

The bad news is: "The repair costs exceed the value of the car."

Too bad. I liked that car. But, Time to go shopping for a new one!

 

1.Don’t give up yet. Spray wurth brand Rost off in cylinder 2 and soak over night. Start car with spark plug out to purge and Reinstall plug. The ring can be carbon bound and need to reseal.
2. Are you using the bleed screw on the thermostat housing to purge air out?
3. Have you checked the radiator manually to make sure that fluid goes it one side and out the other?
4. What part of Maine? There has to be someone that can help!

 

R56devotion
I'll try it!
I'll let you know!

 

I would take it to a 2nd shop and get an opinion. Don't tell them what the other shop diagnosed and see if you get the same diagnoses. I have seen good shops completely miss diagnose. Considering the value of the car I think it would be worth it.

 

Well, ha, ha. If you count me as the first shop, they confirmed what I thought!

But, you're right, I guess. Let me see what tomorrow brings.

 

With regards to the fans turning on when the CTS is disconnected.......this is an ECU activated event. Have you checked the main wiring plug on your ECU to make sure that there is no corrosion or bent pins?

What did the spark plugs look like recently.....if you have a stuck injector it will wash out the piston ring seal and give you crappy compression reading. Hence using the ROST OFF to check that.

 

First I would try what R56devotion said. I hope that helps Check this video