This is driving me mad -

Fan comes on and stays on when the engine is at normal temperature, e.g. when I've been driving down the motorway and pull up at a set of lights, the fan will be on and when I pull off it stays on until I get to about 40 - 50mph, when it switches off (or maybe I just can't hear it beyond this speed?)

LR dealer said the top of the radiator was hot and the bottom luke warm so they decided to replace the Thermostat but that hasn't solved the problem. The car has been LPG converted - could that be linked to this?

It also had a new radiator and header tank about 3000 miles ago.

The car has also been making a terrible squeeling sound since LR fitted the thermostat, they say it is the cover on the bit that comes out of the engine and drives the belt (sorry for the non-technical terms there).

I need to get to the bottom of this as it is really starting to annoy me!!

does it do it on lpg and petrol ? onto no6 Range Rover

Everyone needs a hobby

Yes and I can even switch between the two whilst the fault is occurring and that doesn't make any difference

It doesn't seem to happen when the outside temp is lower than 3 degrees

Why is my viscous fan on when it shouldn't be?

Because its Fu**ed - try a new viscous? '09 Freelander 2 TD4 HSE Auto for the Mrs

Using the works Fiesta 1.6 TDCI Sport Van - CHROME FREE THOUGH

Searching for a nice E63 AMG or S8 V10 to replace my "wonky" TDV8

Try turning off your aircon and see what happens.

might be totally off the mark here, but if you have had a new radiator fitted, could it be an airlock preventing circulation of coolant, the thermastat then gets hot and then the fan cuts in as its over temp?

You say it "Switches off"

You know that the viscous fan is NOT electrical? It's the one that's bolted to the front of your engine, it has a viscous clutch that engages when the heat transfers through the spindle of the water pump. The fan will always spin, but when the viscous coupling is locked it will roar, even at idle.

Are you actually referring to the electric fan? 

Doc - I did think this might be the first thing to try but when the dealer said Thermostat I put my trust in their opinion. What parts would I need to replace, any idea how much I would be looking at?

Vogue - this sounds like a possibility, as one thing the dealer did note was that the top of the radiator was hot and the bottom was luke warm, how would I get rid of an airlock, should the dealer not have checked this before doignt he Thermostat?

Jayzee - I will try without aircon and see if that has any effect

Dan - I know (just about) how the viscous fan works, I think the dealer said it was my viscous and my electric fans that were on at normal temp but I don't 100% trust they are correct that the two fans are on whenever this fault is occurring.

Thanks for the help on this. The fan was roaring this morning (it was over 3 degrees).

If the Viscous fan locked, and the electric fans are on then I would say that regardless of what the temperature gauge is reading the engine is overheating. One relies on mechanical means to engage and the other relies on an electrical sensor. (I believe the electrical cooling fan uses a different temp sensor to the dash gauge)

The exception to the above would be if when you first start the car they don't come on for 5 minutes etc?

Have you run the engine with the cap off the header tank and squeezing the top rad hose to expel any air?

Does the heater get warm, hot or super hot?

Dan 

You can check the viscous coupling easily. With the car cold you should be able to spin the fan by hand.

Many moons ago I had a Vauxhall Ventora with a seized coupling, the car would not go above 55mph due to the power the fan was using.

Ian

Dan - this sounds worrying. The heater doesn't get particulalry hot.

The strange thing is that when the viscous fan is locked on it will usually unlock itself and behave perfectly normally after switching the car off and then back on again.

On occasions the viscous fan will lock on, within 5 - 6 mins of steady driving from cold.

The other starnge thing is that the viscous fan usually only locks on during the first journey of the day. It behaves perfectly normally for the rest of the day.

With regard to the air lock possibility, would this not have been cured when the dealers put new coolant in when they replaced the Thermostat?

I will try running the car and squeezing the top hose though, thanks for that suggestion.

Ian - it spins freely by hand with the engine off.

I think the radiator being hot at the top and cold at the bottom may be the key to this, I wonder if it could be a problem with the water pump?