Overheating - cooling fan doesn't run continuously
 

Hey guys,

Been lurking for a while and finally decided to sign up.

My wife's 2005 justa cooper has had overheating issues for a couple of weeks now. Let me walk you through what's been going on. It originally overheated on the highway while stuck in traffic. We didn't notice until I smelled antifreeze, then smoke poured out of the engine bay and I saw the temp gauge pegged at it's limit and flashing red. Luckily we were at the exit and about 1/2 mile from our destination so we shut it off and coasted there. Upon inspection I saw that coolant had spewed all over the engine. Refilled it and it still overheated at idle. Let it cool down and drove home, which was all highway. Temps were normal the entire time and when I pulled into our driveway the gauge started creeping back up which indicated an airflow issue. Found the 50a cooling fan fuse blown, so I replaced it along with my radiator cap, as it failed a pressure test.

Hoping that was it, I filled and bled the cooling system, but it still overheated while idling. I put it in test mode to read coolant temperatures on the speedo. The fan would kick on and off occasionally with the ac on however, temps continued to climb until it reached 112 degrees or so, at which point the fan would kick on continuously but fail to cool down the engine. On a hunch, once the temperature reached 117 I turn the heater on its maximum setting and temps dropped like a rock. Previous experience tells me this is a coolant flow issue, so I went ahead and replaced the thermostat today.

After getting everything buttoned back up, took it for a test drive. Temps were in the nineties the whole time while driving and it was all looking good for a while, but they slowly started to creep up and over 112. It took CONSIDERABLY longer to overheat than before the thermostat replacement so I'm sure that was overdue but I noticed now that the fan kicks on rather erratically. Essentially it only runs for a few seconds each time. It runs occasionally in the mid 90's with the ac on, but once it reaches 112 or more it'll kick on at high speed for 5-10 seconds and then shut off. It does this a couple of times and continues to slowly overheat. 50a fuse is still good and I swapped the low and high speed fan relays under the hood with the other two (a/c compressor I think and something else, don't remember) but the behavior continues. Any ideas? I'm at wit's end here.

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tl;dr 2005 justa mini overheats. Cooling fan comes on only a few seconds at a time. New thermostat and radiator cap. Fuses and relays seem okay. What's going on?
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I was thinking the water pump but as the temp stays low when you are driving it would be logical to assume the water is going through the system, but then again if the pump impellers are toast then the water may not circulate enough to cool at idle.

Re:
 

I thought of that too, however I get good heat in the cabin even at idle, which logically confirms that antifrreze is flowing through and out of the heaer core, though I may be wrong. Any sure symptoms of a water pump going bad on these cars? Do you have any ideas on the cause of the erratic fan operation? I'll test it today after work just out curiosity.

I also suggest you start watching the coolant level and check the oil cap for any chocolate "milkshake" as you may have a warped head.

Would this be an electrical issue?
 

Oh, that's something I forgot to mention in my post. There's no oil in the coolant or coolant in the oil and a block test didn't detect any combustion gasses in the coolant. I'm pretty convinced that the cause of the overheating is the fact that the fan kicks on for a few seconds at a time and then shuts off, even during an overheating condition. Gauge climbs and temps are 116 or so and the fan remains off. Would that indicate an electrical problem? We're getting some pretty bad rain/flooding right now so I haven't been able to test the fan at low and high speeds directly to a 12v source. Would I be correct in assuming that this is an electrical/airflow issue instead of an antifreeze flow issue? I did take a look at the water pump this morning and it wasn't weeping or anything. Would me disconnecting the ECU to replace the thermostat cause something like this/will it sort itself out after some kind of relearn/time?

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I apologize for all the questions. I've owned a couple German imports but am new to this platform. Thank you for your time!

Rather have you ask a question than ask no question at all. I am wondering if the fan motors are tripping out. Have you tried jumping the motors to see if they will run for a couple of minutes? Be sure to keep your fingers out of the way.

So I went outside armed with a fluke DMM and some test leads and unplugged the fan connector. I assume black on the fan connector (which contacts the brown wire on the vehicle side of the wiring harness) is ground and the other red/blue and red/green are paths for 12v. One goes straight to fan motor and the passes through the resistor mounted on the top passenger side of the fan This is what I'm assuming, of course, but you never know with German engineering :lol:

As you suspected, the fan fails to run at all. If it's anything like a blower motor resistor, when it fails, the current passes through unregulated directly to the motor (hence the loss of speed controls). This would then indicate a faulty fan, correct? Or could the resistor fail in allowing current to pass through it at all? At work (I work at an auto parts store), the catalog lists Dorman 902-726 as a replacement. http://www.partsgeek.com/2jy8fx1-mini-cooper-engine-cooling-fan-resistor-kit.html?utm_source=shopzilla&utm_medium=pf&utm_co ntent=dcs&utm_campaign=PartsGeek+ShopZilla&fp=pp&u tm_term=Mini+Engine+Cooling+Fan+Resistor+Kit

Any chance this could be the issue or will it fail in normally open mode still allowing voltage to pass? Not really concerned about the cost of a replacement fan assembly, just the work required 😐

Thanks for all your help!

There is a sticky thread here about the fan resister. Has more than 50 pages so anything to do with the fan, relays, plugs and resistor are covered.

https://www.northamericanmotoring.co...-solution.html

The symptoms you described make me lean towards three things.
1) The thermostat is a wax core thermostat. It should open when the wax melts but the valve can stick and cause delayed opening or a failure to open.
2) Coolant resovoir cap. These are pressurized and can go bad causing the system pressure to leak and the coolant will not flow properly.
3) Dirty radiator inside or out. Hard water mixed with full strength coolant can cause mineral deposits. If there is not proper air flow on the outside such as bugs or debris being caught in the A/C condenser can cause a limited air flow and the radiator will not get proper air flow.

It really sounds to me like a sticky thermostat but wanted to throw those out. If you squeeze the hose going into the thermostat housing, it should feel like it has give to it. If it is very hard check the exit hoses and see if there is less pressure. This is one indicator of a sticking thermostat. The other symptoms fall into the same symptomology. These are just quick assessments you can do. Be sure to use a towel because it is HOT and check at normal operating temp. You can massage hoses while cold and squeeze them, releasing quickly to help air pockets to dislodge.

Also, are there other issues such as decreased engine power when it gets hot? I have had the temperature misreport before. It is sometimes hard to catch. If you have an infrared thermometer like someone else mentioned, you can find hot spots.

I hope you can drill this down to an answer.