Technical Warming up!

[flip123]

My 2.8Jdt Ducato takes a while to warm up and then it sometime cools down when on say a downhill run. Is this normal or is it the thermostat? Any advise

 

[John C S]

My question would be, how far does the needle drop?

If it drops about 1mm on the guage, that's normal.

 

[PeterM]

If you are used to petrol engines then you will find the diesel slow to warm up. That's because it is more efficient and less energy is going into heating the block.
Mine takes a couple of kilometres to show much warming, and that's for an easy run and warm weather.