4.2 SC
On the third thermostat (the latest LR).
Engine is slow to warm but if the engine is worked it attains and maintains normal temperature but cools right down to almost the blue sector on the gauge when coasting ie descending a hill.
Haven't got much hair left. . . .
TIA Range Rover 4.2 SC
2 Range Rover Classics - one from new but both rusty now.
Rover 3.5 Coupe had since new.
Subaru Legacy 3.0.
BMW K1200RS.

Thermostats are a common fail on these. I've had 2 where the seal has deformed and wrapped around the thermostat causing my cars not to get to operating temperatures. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

Viscous fan issue?

Afraid not. Range Rover 4.2 SC
2 Range Rover Classics - one from new but both rusty now.
Rover 3.5 Coupe had since new.
Subaru Legacy 3.0.
BMW K1200RS.

check if your 4.2 engine has second thermostat on the lower coolant hose. Mine 4.4 ajv8 had this problem, and it was this lower thermostat located in the hose RR HSE 4.4 2006 LPG

Hi, thanks for your thought. I was told on another forum that it had the other thermostat but after buying a replacement I am now assured by my local garage and Matfords that the SC doesn't have it fitted. . . .
I can't believe though that I have bought three new thermostats from different suppliers in as many weeks which could be faulty! Range Rover 4.2 SC
2 Range Rover Classics - one from new but both rusty now.
Rover 3.5 Coupe had since new.
Subaru Legacy 3.0.
BMW K1200RS.

Neither can I, have you trended the actual temperature on a scan tool? Just to check that the transmitter is working OK..

Many thanks.

I've looked it up on Rimmer's site where it states that the part is for both engines!

How can a main dealer get it wrong??

The part should be coming in a day or so - fingers crossed and I'll let you know. . . . Range Rover 4.2 SC
2 Range Rover Classics - one from new but both rusty now.
Rover 3.5 Coupe had since new.
Subaru Legacy 3.0.
BMW K1200RS.

It was indeed the 'secondary' thermostat that had failed - all fixed and thanks for your help. Range Rover 4.2 SC
2 Range Rover Classics - one from new but both rusty now.
Rover 3.5 Coupe had since new.
Subaru Legacy 3.0.
BMW K1200RS.

Incredible and amazing! 2012 Supercharged L322