Once the tstat is fitted will bleed and see how it runs.

That's what I thought, but the lad in the garage explained that if it's overheating between 3-8mile it's nearly always the tstat as the entire coolant hasn'the heated enough to warm the rad...

As a complete novice I've not heard of that before, what is it?

Hi all, New to the site and to the Range Rovery family. No-one wants to know about me so let's get down to Ranger. OK so it's a 1997 P38 4.6 V8 LPG conversion on 133k, considering the age it's immaculate inside however as recent events have confirmed, the engine area isn't. Started overheating...

Standard overheating issues for the '97 P38 4.6 V8.. :(