That's how engines work. This isn't rover specific. Your mate was right.

Of course it's cooler on the outside of the engine as you're driving - you're moving air and cooled coolant over it. Heat travels from warm to cold, this is basic physics and how your radiator and air conditioning work. When you stop (and stop moving air and coolant over and through it) the hotter inner parts of the engine are going to continue soaking heat (that is now not being dissipated) into the outer portions of the engine. When you open the hood, heat is released and carries even more away because of convection.

 

Found this article. I have problems with my old 1985 Range Rover with high engine temps. I removed the radiator and it was cleaned out 12 months ago. I cleaned the bugs from it and the A/C evaporator with compressed air, followed by high pressure cleaner (being very careful with the fins). Checked fan belt tension. Replaced radiator and flushed 5 times with water before adding coolant system cleaner. ran engine and temp came to normal (71C thermostat fitted). Then went for a drive and when the auto transmission temp gauge started to climb, the engine temp did likewise. using an infrared thermometer I got 92C at top inlet of radiator, 71C at outlet at bottom of radiator, and ambient air temp was 36C that day. The radiator is working due to 20C change in water temp. Fans are pulling plenty of hot air through. I feel that the under-hood temp is heating the auto trans which then heats up and passes its heat back to the engine by the stock cooler mounted in front of the radiator. The whole car is standard. I am going to again check the temps of the inlet & outlet pipes of the trans cooler. Does anyone have any ideas on how to reduce these temps? Thanks, bushtrev.

 

Sorry to hear that. Better post this on the Range Rover Forums, our heating problem here is much worst. Good luck but replace thermostat first. You top only 197 degrees. Here we have 220+. Cheers

 

This issue was discussed at nauseam on my old Jeep ZJ forum, where the 5.2L and especially the 5.9L suffered from crazy underhood temps. It seems the best solution for that truck was the factory 5.9's hood vents:



There was quite the discussion about negative pressure at low speeds and all kinds of other stuff that's hard to measure, but the general consensus was that the Jeep engineers knew what was best and most went that route with their I6's and 5.2's.