Mini pukes coolant from expansion tank cap

Shane Owner/Technician Alberta Posted   Latest  
Resolved
Driveability
Drivetrain
2009 Mini Cooper S 1.6L (N14B16A) 6-spd (GS6-53BG) — WMWMF73529TT94514
Overheats
Coolant Flow
Poor Heat

Hi guys, I received a 09 Mini Cooper S that had come from another shop which gave up. I don't have a lot of experience with Mini's but wanted to try to help the guy out. The vehicle overheats after about 30 minutes of driving, but only once you come to a stop and/or shut it off. There's no temp gauge in the car and no overheating message never gets displayed, but the expansion tank will puke a little out thru the cap. The heat from the blower is sometimes good sometimes not, like a typical air lock, which was my first guess. The upper rad hose and heater hoses are hot, but the lower hose is cold. The Electric fan does work and will run on for a few minutes after shutting it off. 

The previous shop replaced: Turbo (No one can tell me why), water pump, aux water pump, rad and thermostat. They told him it must be his head gasket. I checked compression - good and even across all 4. There's no signs of coolant and oil mixing anywhere, and there's no bubbles in the tank when its running, and no external leaks.

I started with a vacuum bleed as per Mini's coolant fill procedure. After that I put some pressure into the system with a pressure tested and then bled any air from the thermostat bleed screw. No change.

We left the pressure tester on overnight and it dropped about 5psi. Found 2 small leaks, one a hose clamp and one an O-ring I switched out. I replaced the expansion tank cap and installed an OEM thermostat as the other shop used aftermarket parts. Back flushed the heater core and have good flow in both directions. Refilled with proper bleed procedure. No change.

My plan tomorrow is to disconnect the upper and lower rad hoses at the thermostat and force water thru, to check for any blockages, then crank the engine to see if water is being moved by the water pump (I checked the return line in the expansion tank and there is a flow, although it seems weak to me).

As mentioned I don't have much experience with these, but it seems to be a pretty basic system. Any ideas or tips would be appreciated!

Thanks in advance.

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Rusty Owner/Technician
Massachusetts
Rusty
 

I’d be sampling the cooling system gasses for CO2 with a block tester or 5 gas. i know zero about euro stuff but the symptoms scream HG leak to me.

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Shane Owner/Technician
Alberta
Shane
 

I've never done that before, I'm assuming you just hold the sniffer above the coolant and not submerge it?

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Rusty Owner/Technician
Massachusetts
Rusty
 

I’d lower the coolant level and run it till it’s purging. Then sample the vapor. Pretty sure you’ll see elevated CO2 if the HG is at fault.

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Ronald Mechanic
Alabama
Ronald
 

Hi Rusty​.​Been a long time,glad to see your name again.

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Boyd Technical Support Specialist
Georgia
Boyd
 

I see you survived your vacation. Try to stay cool over there.

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Rusty Owner/Technician
Massachusetts
Rusty
 

Old names, old times 😉 Nice to interact again.

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Louis Technician
California
Louis
 

Hey Rusty, I believe you would be looking for elevated HCs, correct ? I've done that from time to time being careful not to suck in any coolant. With an auto trans, power braked it for about 10 sec. then sniffed it, any HCs showed up, done. Louis N.

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Rusty Owner/Technician
Massachusetts
Rusty
 

Sure, HC will show up but CO2 will be more obvious.

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Shane Technician
Massachusetts
Shane
 

If you have a scope and pressure transducer put it in the radiator and crank it

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Mickey Owner/Technician
Florida
Mickey
 

Make sure it has a good OE or continental belt and that the friction wheel doesn’t have any oil or coolant. Also make sure that the radiator hoses attached to the thermostat are not swapped. Easy to do.

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Dee Technician
Tennessee
Dee
   

I have (2) R56 MINIs…..You mention the other shop replaced the thermostat. Pretty much every name brand thermostat I've seen have crappy Chinese temperature sensors installed. Either they are way off temp wise or fail in a very short period of time. This of course causes havoc with the computer and cooling fans etc. It might be worth your time to swap in a oem MINI coolant sensor. Mickey has…

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Obie Technician
Washington
Obie
 

Before you get into alot of stuff, test the cap. Verify fan has two speeds. Low speed failure is not uncommon. Monitor temp with a scan tool to see what is the real temp. Some turn the pump with the back of the belt. Don't recall which ones. If so look at the belt and pulleys Inc the front damper. Find out where the pump came from. There are junkers sold every day. Also check aux water pump…

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Shane Owner/Technician
Alberta
Shane
 

Cap is new and OEM. I looked for actual coolant temp in live data but couldn't find it in Autel. Maybe Snap on will have it. A couple guys have mentioned check both fan speeds, I'll definitely look into that as well. I checked the aux pump and verified it runs on for about 5 mins after shut down.

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Richard Technician
New York
Richard
 

I agree with Rusty, this sounds like head gasket failure. If you can test it with a 5 gas analyzer, that would be best.

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Mehboob Owner/Technician
California
Mehboob
 

Check Radiator fan resister for low speed. it causes engine overheating at idle when car is not moving. Does it overheats when car is moving? Blown Head gasket usually sets misfire fault codes. You can unlock cluster and check engine temp. there is no water pump belt. It has special tensioner. Make sure water pump is rotating. After market water pump does not circulate coolant properly at idle…

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Shane Owner/Technician
Alberta
Shane
 

It doesn't overheat while moving. No misfires and the plugs look perfect. Do you know the procedure to unlock the cluster? I haven't been able to find actual coolant temp on autel scanner. I'll double check the pump and pulleys tomorrow.

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Randall Technician
Pennsylvania
Randall
 

Shane, You can typically get accurate engine temperature from generic or global data, but cooling fan command will not be listed. Verify the sensor is correct on a cold start if possible. Crank the engine WOT “clear flood mode” while someone watches for coolant level rise and/or for bubbles in the system. If it doesn’t clear flood crank, then jump out the starter. Lots of good suggestions…

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Stacey Owner/Technician
Florida
Stacey
 

I agree with the mentions of checking the fan runs on both speeds. Another thing you should check is that the friction wheel is engaged and turning the water pump. Lastly, if you have not done a leak down test, I would suggest doing that. Good luck.

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Mehboob Owner/Technician
California
Mehboob
 

Check YouTube how to unlock mini cooper cluster for temperature. from your information to me coolant circulation or heat transfer may be the cause,

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Cody Diagnostician
Illinois
Cody
 

This head is blown, we see a lot of mini head gasket failures. Test for co2 or hydrocarbons to confirm

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Helpful
Jordan Apprentice
Ontario
Jordan
 

Second this^ . Heat is intermittent because air trapped goes to the highest point (heater core) I bet if you step on it the water pump spins fast enough to get coolant to the heater core. And make heat, But when cruising or idle, no heat. Especially if boiling over. If no access to a combustion tester, T into the overflow line with a pressure gauge and hose, 30psi should be suffice and route the…

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Bill Owner/Technician
Idaho
Bill
 

I agree with rusty. It sounds like exhaust gases getting into cooling system.

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Jon Owner/Technician
California
Jon
 

That thing is done. Do yourself a favor and tell the owner to trade it in.

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Shane Owner/Technician
Alberta
Shane Resolution
 

Thanks for all the help guys, it is the head gasket. A leak down test revealed it, but not through bubbles in the coolant, we performed it with the coolant drained (because we already had it drained) and I could hear air flowing and slight gurgling. Tried to use our 5 gas analyzer but found it non functional after sitting for a long period. Needs to be sent to Snap On for 2 filters and…

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Interesting
Shane Owner/Technician
Alberta
Shane Update
 

One more question for those familiar with Mini, customer OK'd the repair…at 150,000kms/93,000 miles is now a good time to replace the timing chain while we're in there? I'm more familiar with N20 engines than N14.

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Mickey Owner/Technician
Florida
Mickey
 

I vote yes.

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Shane Owner/Technician
Alberta
Shane
 

I'll examine it. Customer is proactive and is willing. Just looking for input if it's a common issue on this N14 engine.

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Dee Technician
Tennessee
Dee
   

YES!…the R56 engine set up is almost identical to the N20 engine timing chain wise. Just a slightly smaller version guides. Have (2) MINIs…and we also own a BMW N20 (strange but true). I just got done putting new chains and guides in both MINIs. Our N20 had a chain failure last fall @ 74k miles with no warning. Lucky for me the N20 valves didn't get bent. I was actually more worried about…

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Steven Technician
Washington
Steven
   

YES! The other concern is the fact that it has overheated so many times. It’s a gamble to repair it.

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