Why does my defender 300tdi overheating 4x4ing on beach only. I have discovery wheels on her and wondering if that's the problem as never happened with the standard rims. Any help would be great

Low range high revs?
What cooling fan fitted?
Shroud still fitted?
Got coolant?
Stat okay?
More endless questions as just guessing from limited info supplied

If the sand is slightly soft there’s a heck of a drag on the transmission to keep him/her moving

Got an electric fan fitted with no shroud but fan is right on radiator sucking air through and coolant is fine. Travel in high range as it does it easy but I don't know about stat, Is there another stat that can be fitted without that stupid bypass or maybe that opens before 88 degrees

It may be worth checking your radiator. They can look OK then the fins turn to dust when you touch them, so their heat exchange affect could be reduced quite a bit.

Without a cowl your fan is only going to draw air over the area your fan covers so reducing the area of your radiator that gets sir drawn over it. I presume if you are on a beach you are not moving very fast so the air passing over the rad is only where your fan is where normally the vehicle moving would provide some flow.

As has been said above, moving on sand will take more effort from the engine than normal driving.

I am no expert, so please don't take my comments as an expert opinion, but I have had two land rovers where the rad looked OK only for them to turn to dust when I touched then - one resulting in a cooked V8!

Is it actually getting hot, or is the gauge just showing hot?