Radiator fans cutting in and out

[RichardH]

Hi all, bit of help please.

When the car starts from cold and is warming up the fans keep cutting in every approx 30secs and run for 2/3secs before cutting out. The car idles correctly at a steady 1k rpm and obviously the engine temp is way below the usual trigger point. I know there is more than one fan sensor, but my gut feeling is that it is probably the sensor for the radiator fans and recirculation pump. Before proceeding is this the likely candidate, or should I be looking/testing elsewhere.

Many thanks

[chrism]

viewtopic.php?f=134&t=30441&hilit=thermostat+fans
https://www.youtube.com/watch?v=tfj3dUZTYJY

RichardH if you look at these posts they might give you some background info.

Using them I think I'd do the fan and auxiliary fan sensor tests first, expecting the tests to show them working as expected, then suspect the CTS or 'fan switch'.

These are expensive to replace or use as a substitute; 'peteoddcar' on this forum has put together a simpler, cheaper alternative that's working permanently (now) on his m100 and would certainly be a cheaper way of substituting this sensor (or perhaps a used unit might be another way?)

When you read these posts you'll see that there's another sensor that's part of the picture. It's an ecu/temp sensor that's very close to this CTS unit - and under them all is the thermostat. Imo these, too, are candidates that can cause cooling 'upsets'

Keep us informed of your quest, feedback is the lifeblood of this forum. (This is how we all learn about our m100s. Quite often folks ask for help then go silent and we don't know if our advice has been relevant or useful...)

Also...'ElanScan' is a really good tool that can show you if you're getting to operating temp. If you're ticking over at ~1000rpm I suspect you are - and that might rule out a thermostat issue. Perhaps someone nearby might 'plug you in'?

edit - just a thought - is the white nylon push-on connector to your CTS 'sound' and not loose? Or tightened up okay to earth properly on the engine block?

[Fredjohn]

Before looking at temp sensors, check the fans' earth contacts. They are down below behind the bumper. It gets a bit rusty down there!

[RichardH]

Thank you for the reply, will hopefully have a look this weekend weather permitting!

[RichardH]

Reason found. Aside from the sensors on the thermostat housing, when looking through the service manual, there is a pressure sensor for cars with a/c which turns the fans on/off regardless of engine temp. My car has a/c, and this was causing the continual cycling, presumably as the car was not moving. With the a/c turned off the fans did not run until the 3/4 mark was reached as expected, so thankfully all seems to be working as it should.

[chrism]

RichardH good to get feedback, thanks. That's something we've all learned about I suspect...