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 Cooling fan on nearly all the time

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Dermottdog
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PostSubject: Cooling fan on nearly all the time   21st April 2015, 19:19

Hi Mini nuts

Not posted for a while.

Had a temp sensor changed recently. Ever since, the cooling fan seems to come on when I'm in free flowing traffic going at 40mph for example. In the 3 years before the sensor change, we never heard the fan run. The temp gauge in the hidden menu says the car is running between 105-108 degrees. The fan is programmed to switch on at that temp. I would think that the 'normal' running temp with a good flow thru of air would be closer to 95 degrees and therefore no additional cooling from the fan would be required. Could it be that the sensor is reading too high (ie the engine is running at say 95 degrees but the sensor is indicating a higher temp and in turn switches the fan on).

Been back to the dealer today and they said the temp of 105-108 is spot on but I think they perhaps misunderstood my issue.

Who knows, it might even be that the original temp sensor was reading a lower temp and therefore never, ever switched the fan on.

Your input and opinions would be most welcome - Rob
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PostSubject: Re: Cooling fan on nearly all the time   21st April 2015, 21:05

Not sure I can help Rob....

Now the weather is warmer my fan comes on when I get home, about 8 miles but doesn't going to work!

Do you have the A/C on? as pretty sure I've read that the fan will always be on!

I do know that they run very hot but don't know the temp's

Might be worth giving Will or Graham a call at TWG (club sponsors)

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Dermottdog
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PostSubject: Re: Cooling fan on nearly all the time   21st April 2015, 21:14

Thanks Dave. Yeah I think Will is the next step. I'm not worried about over heating but have a concern that the fan, running on its highest speed constantly, won't come on when really needed. The original fault which required the temp sensor to be changed in the first place was the revs went up to 3k on start up. This then developed into the fan starting up after 30 secs on a cold start before settling down. I will talk to Will after I come back off holiday. It's more of an annoyance than anything else. Thanks again.
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PostSubject: Re: Cooling fan on nearly all the time   29th April 2015, 10:06

Hi Dermottdog. When you posted this on another forum recently I copied a reply from 'robbo mcs' on NAM which IMO explained my own problem of 2 yrs ago and seems similar to yours. I think it might help others to share robbo's answer on this forum too...
BTW have you 'sussed' it yet?


Depends!!

To understand what is going on here, you have to understand that there is a temperature sensor that tells the ecu what the temperature is, and a mechanical thermostat that opens at a certain temperature and regulates water flow and therefore the temperature.

What is supposed to happen is that the mechanical thermostat is set to 105C (221). When the car is moving with good radiator flow the temp should stay at roughly 105. Once the temperature goes > 106 (223) the electric fan cuts in. This usually because the car is stationary, with no airflow.

The problem is that the mechanical thermostats seems to be a little inaccurate and out of sync. There are a whole lot of thermostats that seem to run at 107-108C (224-227F). What happens in this instance is the thermostat doesn't open water flow properly until it reaches its temp, so driving around the temp will be 107-108C. This confuses the ecu, as the temperature sensor reads >106, so it activates the fan.

It is also possible to have the reverse problem, ie an accurate thermostat but a miscallibrated temperature sensor which reads the water temp higher than it actually is, which can produce exactly the same problem.

If this is happening, the fan is not just running when you stop the car, but nearly all the time, even driving around. When you stop it will run until the temp drops to the 106C number.

So if you are lucky and have a "normal" thermostat that runs around 104-105C you won't get the fan operating when you stop very often. If you have one of the thermostats that runs at 106-108C you will get it a lot.

Does this matter? Not really from an engine point of view. However, it must be increasing the risk of fan failure in the long run.

Also, just out of interest, there are actually 2 thermostats operating in 2 stages. The main one runs as described above. There is a second one set to 85C (185F). When the ecu detects high turbo load from aggressive driving etc it opens the second stage, and the temps drop down significantly.

Robbo
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PostSubject: Re: Cooling fan on nearly all the time   29th April 2015, 10:43

Thanks cjm. No, I haven't solved it yet. The more I read the info in your post, the more I'm convinced that there is a mismatch/conflict between the temp sensor and the thermostat. I will investigate when I get back from holiday. Will at TWG is a good bet but they are a fair way away. Will needs to do house calls I think....
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