Hi chaps. I've moved this from faults and fixes to where it's supposed to be.
A while ago I replaced the thermostat in our 2005 RRSS as the temperature gauge was showing erratic readings. I also put in a new temp sensor.
Well, the same is happening again..
Cold start engine temp goes up to middle as it should but then it drops to 1/4 and the viscous fan is running - this is within 15 min of driving so the fan should not be on. Eventually the gauge shows just under 1/2.
If I stop the engine for a few minutes and restart it runs normally - almost like its reset itself.
Coolant level is ok.
Update - I replaced the cts again and it was ok for a week. Its now reverted to as before. It can't be 3 failed sensors. And I bled the cooling system via the small cross head screws.
My Foxwell 520pro does not seem to want to give me live engine data either--well if it does I can't find the setting - so I can monitor the real engine temp. It has no codes shown either.
Has anyone got any ideas? This one is baffling me. It started doing it after the alternator was replaced and the fan had to be taken off. Could that have anything to do with it?

Bump..

Sounds like your viscous van is running when it should not be

All this agro started after it had a new alternator fitted. Low and behold the fan had to come off to replace it..
Any ideas as to why the fan should run when it's not supposed to?
Is it electricaly controlled or old school viscous controlled?
On the Foxwell there is an option to run /test the fan. I may have a play with that.
The fan being on at the wrong time does not explain the rapid drop in indicated temp on the guage though. Normally the guage stays at 1/2 way with fan on or off I think.

Usually because there to be honest they lock up so then they can be on all the time you need to see if it’s free when it’s up to temp they should only really come on when first started and yes they are mechanical as far as I am aware :thumbsup

They are mechanically driven, but can increase speed by electric command. (if they are like the diesel)

CHeck the cable is plugged in (near the coolant tank)

When you press the ECO button on the climate panel the fan note should change.


Start with the ECO Light on, start engine,
Wait a minute, then press ECO, after 30 seconds maybe the fan note should change

I've just had a look. It's plugged in and I can't see anything untoward. The engine is cold and I can spin the fan by hand but it won't spin freely if you know what I mean.
Ill check the eco button test on Saturday when I'm going to use it.

The viscous fan is exactly that; Viscous. It is mechanically driven to the shaft, but fluid and heat then have an effect on how 'locked up' it is.
It will run with the engine, but not locked, so not at full speed. The fan will also feel like it has some drag with the engine off.

The option to run the fan on the diagnostic tool, is likely for the Aircon Fans, and not the Viscous Fan.

As stated, these usually fail in the locked position. 2011 MY D4 HSE
Previously 2001 D2 TD5, 1996 D1 300Tdi, 1985 90 2.2 petrol.
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It doesn't have any aircon fans only the viscous.
The diagnostic tool states 'viscous fan run test'- whatever that involves..
Ill take a look tomorrow as the car will be at home.

Dont think the tool would be able to warm the fluid up enough to lock the viscous unless as i suspect your unit is faulty

There are some electrics that can bypass the vicious or something.

This may be a coincidence but today I drove it without the LPG on as I had ran out and guess what - normal operation..
Could there be a link?

Dont get what you have when i run mine on lpg but you never know do you know who fitted the system to your car

No, it was on it when I bought it. Its a proper job - BRC kit with auto valve lube etc.

I'm not sure it's the fan. Yesterday I used it a drove 1.5 miles, stopped at some traffic lights and the temp gauge suddenly started dropping fromm half to 1/4 all in about 5 seconds.
When I pulled away the fan started and stayed like that until I got back home. I don't know if it coincided with the lpg coming on as I wasn't looking but there was a noticeable change in engine running at idle - it sort of stuttered a bit. Very similar to switching to lpg.
When i get chance I'll turn the lpg off and run it to see what happens.
I was always under the impression that lpg runs hotter tho'?