pannawonica wrote:

82'C thermostat only effective on temperature, no difference on fuel consumption! I would look elsewhere for the answer. I did not reference in this instance 130km/h for high temperature, 110km/h is more than enough! when towing. I have noticed for a fact that at lower ambient temperatures in the early morning this is not a problem, what does that point too? Reference Aulro regarding the upgraded Ali sport upgraded radiator, I have no doubt it's a good product and does come up too it's claimed specification. However that been said, it doesn't always cut it out here.

Beery wrote:

Bergos, I think driving to the conditions is the best advice I can give. Of course driving at 130km/h in 40+ degree temperatures in a Defender is going to cause sky high fuel consumption and overheating.

I agree with Pannawonica. I've installed the 82C thermostat too and it helps. But only when you are operating within the cooling system's capacity range (i.e. coolant flow, radiator capacity, airflow etc.)

If you're going to keep driving in the same style then you'll want to look at improving engine bay airflow, decat, egr delete, changing glycol concentration to 30% and adding wetting agent, bigger radiator etc.

Another thing worth trying, which I'm yet to do, is blocking the coolant flow through the heater tap. It's a bypass type, meaning there is a constant flow of coolant bypassing the tap when its closed. That means its also bypassing the radiator and getting sucked straight back into the pump and back into the engine.

Your vehicle is ten years old. Has the cooling system ever been properly cleaned internally? Are the radiator fins clean? Have you checked that the viscous fan clutch is locking up properly?