Yes, it might be complicated by an an air lock that hasn't been bled out of the system as well as, or instead of, the sensor. That's happened to me, too.

Let us all know when that fan behaves itself and post the new scangauge values. (I bet they'll be back to the original values + you won't hear the fan!)

Echoing SuperGreg's sentiments...

 

Thanks guys. My mechanic seems pretty bent on figuring this out, so it's just a matter of time!

 

I finally connected my car up to a scanner.

Basically 226 F is the operating temp and fan stays on 30seconds after shutoff as well.

Normal?

 

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

 

Thanks for this informative post.

I have done some more testing. On hard acelleration I can get the temp to go around 230 then I noticed all of a sudden the temp dropped about 10deg and then slowly went back on. Maybe something else was kicking it.

Additionally, during normal operation at 226F the fan always remains on. So it seems I have a faulty component. What needs to be done exactly to remedy the problem? Just change the thermostat?

 

It is normal for the temperature to briefly spike and exceed the thermostat level when you first start driving hard. It takes a little while for the water to start cooling, so seeing a brief spike to 230 before it starts to drop again is normal.

Replacing the thermostat housing which contains all these components should fix the problem. However, you may just get another one the same, as there seems to be a lot of variation in them, and lots behave in this way.

It is not really damaging your car, just annoying. If it is under warranty it is worth fixing.

If you want to see it drop down to close to 185 to check the second stage is working go and find a quiet back road with no traffic. Drive from a standing start and accelerate full throttle to red line in second gear, brake as hard as possible back to close to standing and repeat this 3-4 times. You will see the water temp start to drop dramatically.

 

What happens exactly in order to get the temps to drop down to 185? Does the fan speed increase or something more dramatic? Also at what temperature does the second stage get triggerd at in order to drop temps to 185?

 

Thanks robbo mcs. Your explanation really convincingly explains all my rather convoluted set of experiences when my dealer tried to fix my 'fan running when hot' and 'fan run-on after switch off' from new in 02/12. For me it was, firstly, a sensor replacement called a new thermostat, then a thermostat housing + sensor replacement (which actually fixed it) with bleeding then the new cradle + re-sited sensor 'enhancement' which continues the fix...

I seem to remember around mid 2012 that there were a "bad batch" of thermostats that NAM people were warning about causing N18 fan running problems, too. Sussed; thermostat mismatched to the sensor!

So, it seems simple to me; more quality control issues along the same lines as wrong chains, faulty pumps, weak gearboxes and clutches, leaking oil solenoids/sumps/tensioners and others I must have suffered information overload on...

 

In a cars cooling system water does not circulate through the radiator non-stop, otherwise on cold days your water temp might be only 100F, which would be bad for your engine.

In a simplified version of what happens, the first thermostat opens when the temp reaches a preset level (105C/221F) and allows water to circulate through the cooling system. Once the temp drops below that level it closes, so the water temp heats up again. So the thermostat is constantly opening and closing to allow circulation and cooling of water and keep it to the desired temp.

Our minis have a second thermostat set to 85C/185F. When the ecu detects conditions likely to produce significant heat requiring further cooling it can control the opening of this thermostat. This thermostat then operates the same mechanism as the main thermostat, but just at a lower temperature. This has nothing to do with the fan. It only lets more water circulate through the radiator. This second stage is not triggered by a certain temperature, but by certain parameters in the ecu, eg engine load, boost etc etc

In practice you will virtually never see the temp at 85C/185F. The type of driving required to trigger this second loop generates a huge amount of heat, so that even with this second stage open the temp usually sits in the 90-100C (194-212F) range. Effectively in this mode the thermostats are fully open, allowing maximum circulation of water through the engine and cooling system.