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Mpi Coolant Woes... At My Wits End :(


Best Answer nitrodave , 21 July 2020 - 01:59 PM

Ok... problem solved it would seem! I’m elated!

Took the thermostat out and tested it in a cup of boiling water and it didn’t open. The old one also failed to open when tested.

As suggested above I also tested the dash gauge behaviour from cold and seems to be fine. Starts cold and rises progressively.

However, I ran the car with no thermostat and it still boiled over until I manually kicked on the fan.

I then took the cap off and put a small piece of hardy gaffer tape over the valve hole and ran the car up to temp again.

Just as the coolant began to rise the fan kicked in!

Turns out the new cap was at fault all along. Can’t believe I’ve had two new caps fail and a new thermostat fail.

I’ve ordered a blue seal bmw cap and also a Volvo cap and will try these now.

Also, how important is a thermostat? Can I just run without one and if it’s not recommended where’s the best place to get one from? I purchased all my parts from minispares and few somewhat disappointed in their performance. It’s not their fault though, they didn’t make them Go to the full post


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#1 nitrodave

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Posted 20 July 2020 - 04:47 PM

I'm now in pretty desperate need of help and tried everything after reading all I can from the forum. Really hoping someone has the answer! PLEASE...

 

Problem: engine runs fine and car runs well. Once it's up to temp and idling the expansion bottle fills, pressurises and eventually the cap is overcome until I pull the plug off the sensor to activate the fan and blip the throttle to flow the coolant. After that and with the fan still running, the coolant immediately drops back down to where it should be and does not boil again.

 

The fan never trips on by itself. It only comes on when I pull the plug on the temp sensor on the thermostat housing. The fan is very effective and it can then sit there all day idling and the coolant doesn't rise back up or show any signs of misbehaving.

 

There is plenty of hot air in the cabin also suggesting there isn't an airlock.

 

In an attempt to cure this I have fitted a new expansion bottle and tried 2 new caps. Changed the water pump for a minispares EVO, fitted a new thermostat, new temp sensor in the thermostat housing, done the wiring loom upgrade, fitted all new coolant hoses, flushed the block through until clear water flowed, took the rad out and flushed that through also and it flows well. I can feel heat all across the entire radiator when it's up to temp. I have swapped relay for know good ones, filled with G48 coolant... and the heater matrix in the car is relatively new also. I just seem to be throwing money at it trying to fix this.

 

Am I correct in thinking that by pulling the plug on the sensor and the fan coming on that the ECU is functioning correctly, the relay is doing it's thing and there's no problem with that and associated wiring?

 

I don't see any symptoms of a head gasket failure. Oil and coolant are clear, I'm not losing coolant, there's no smoke out the exhaust and it runs well and behaves with the fan running. With the fan on it behaves just fine, so I don't think that's an issue

 

To summarise. With the fan running the car runs and behaves brilliantly. It's got a flushed and refreshed coolant system, but the fan fails to come on by itself.

 

I'm based in St Albans, so if anyone is local how to cure these issues, I'd be willing to reimburse with a few beer tokens!

 

 

 



#2 nicklouse

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Posted 20 July 2020 - 04:55 PM

Are you aware of the cable tech change https://www.minispar.../YMQ105690.aspx



#3 nitrodave

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Posted 20 July 2020 - 05:09 PM

Thanks, yes I have fitted that also. Made no difference

#4 tmsmini

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Posted 20 July 2020 - 05:09 PM

Are you aware of the cable tech change https://www.minispar.../YMQ105690.aspx

Sounds like he took care of that, "done the wiring loom upgrade"

 

I think you are going to have to check the wiring and trace the temp sensor wires back to the ECU to check continuity. Also be a good idea to check the ground locations for the MPi.



#5 nitrodave

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Posted 20 July 2020 - 05:17 PM

Thanks... I haven't actually checked that wires from temp sensor to ECU for continuity, but assumed that when i pulled the plug fromthe sensor and the ECU triggers the fan, that this would be ok. I'll pop out shortly and test these



#6 tmsmini

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Posted 20 July 2020 - 05:25 PM

This document:

RCL0194ENG-cdxn990e Electrical Circuit Diagrams

 

http://www.theminifo...ttach_id=193892

 

 

shows the cooling system diagram and the MEMS diagram. It looks like the sensor gets both it signals from the ECU. The fan is grounded directly.



#7 Quinlan minor

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Posted 20 July 2020 - 05:57 PM

Does the temperature gauge, on the dash, indicate that the engine is overheating? The signal for the gauge is taken from the temp sensor. Check the resistance at the temp sensor pins:
1:When the engine is cold
2: While the engine is heating up
3: When it’s starting to boil
It may be faulty.
If it checks out, I would suspect the header tank pressure cap. I’ve had quite a few duff ones over the years. Try to find one of the BMW ones (with the blue sealing ring).

#8 nitrodave

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Posted 20 July 2020 - 06:37 PM

I just tested continuity from the sensor wires to the ecu plug and everything checks out fine.

I should add a little more detail to the story in case it’s of any use. When I got the car in June it did exactly this. I then fitted a new expansion cap and it behaved and the fan came on. Great... or so I thought.

I have since restored the car and done a lot of work to it. I didn’t touch the engine bay though, just bodywork.

After completing the restoration (I’ll post that up in another thread for all to see) I took it for MOT and the water pump failed. It was original to the car so it was no surprise. I changed the pump and it’s been doing this since.

I then decided to completely refresh the cooling system as it had horrible free silicone hoses and everything looked original. It was something I wanted to do anyway and I needed to try and resolve this so I replaced everything for new parts, but I’m still getting problems.

I don’t have a multimeter to test the sensor, but I’d be surprised if it’s at fault as it’s new. I’ve just bought one on Amazon and it arrives tomorrow.

I have also ordered a bmw blue seal cap which should be here by the end of the week, but I’ve tried 2 new caps already with no change in behaviour.

The only things I can think of are an electrical fault not tripping the fan, or an air lock causing boiling and expansion before it gets to 105c to trip on the fan.

Should the top hose pressurise? It doesn’t seem to be at any time.

The temp gauge seems to function ok. It goes up to just under half way. Thing is, it still works even without the plug on... even when I pull the plug, ignition off, arm the alarm, disarm and restart. The gauge still reads.

#9 Quinlan minor

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Posted 20 July 2020 - 07:06 PM

Evidence points to a lack of pressurisation.

I had a problem on mine and two new caps left it boiling. A blue seal one fixed it!

 

Do me a favour, with the engine cold, ignition 'Off', pull the lead off, ignition 'On' and see if the temperature gauge is at 'Cold' or 'Normal'?



#10 nitrodave

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Posted 20 July 2020 - 07:14 PM

Engine is hot still as I’ve just run it up to temp again, so I’ll try that in the morning.

What would they tell me? I’m a little stumped that it still reads temp on the garage even with it unplugged from the sensor.

I’ve ordered a blue seal cap. Really hoping that’ll do the job!

#11 nitrodave

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Posted 20 July 2020 - 07:14 PM

Gauge not garage! Damn phone :)

#12 Quinlan minor

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Posted 20 July 2020 - 07:25 PM

What would they tell me? I’m a little stumped that it still reads temp on the garage even with it unplugged from the sensor.

I'm wondering if the ECU picks a null point, when the input is disconnected.

 

The other piece of equipment that would clarify things would be an infra-red thermometer so that you could establish, with certainty, whether it's over heating or boiling due to lack of pressure.

A pressure tester would also be handy.


Edited by Quinlan minor, 21 July 2020 - 07:56 AM.


#13 tmsmini

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Posted 21 July 2020 - 12:38 AM

The top hose should pressurize. Have you checked the code reader thread to see if anyone is near you to see what the temp sensor indicates when reading from the ECU?

Did you test the thermostat before installation? And that it is in the right side up?


Edited by tmsmini, 21 July 2020 - 01:15 AM.


#14 nitrodave

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Posted 21 July 2020 - 01:59 PM   Best Answer

Ok... problem solved it would seem! I’m elated!

Took the thermostat out and tested it in a cup of boiling water and it didn’t open. The old one also failed to open when tested.

As suggested above I also tested the dash gauge behaviour from cold and seems to be fine. Starts cold and rises progressively.

However, I ran the car with no thermostat and it still boiled over until I manually kicked on the fan.

I then took the cap off and put a small piece of hardy gaffer tape over the valve hole and ran the car up to temp again.

Just as the coolant began to rise the fan kicked in!

Turns out the new cap was at fault all along. Can’t believe I’ve had two new caps fail and a new thermostat fail.

I’ve ordered a blue seal bmw cap and also a Volvo cap and will try these now.

Also, how important is a thermostat? Can I just run without one and if it’s not recommended where’s the best place to get one from? I purchased all my parts from minispares and few somewhat disappointed in their performance. It’s not their fault though, they didn’t make them

#15 nicklouse

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Posted 21 July 2020 - 02:06 PM

Any place that sells them they will all be from the same supplier. But please note some that do fit are not actually mini ones and don’t have the small air bleed hole in the side of the ring. There is normally a little wiggly thing there that closes the hole when the air has bled out.






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