So this not a "oh my good my truck is overheating" question.

Basic background

My truck runs at 177 to 185 at highway speeds 60 to 70 mph in 75 to 87f temps.
The A/C Helper fan is out but running A/C at high speeds only adds 5 -6 degs
At speeds between 30 and 40 mph 174 to 177f temps are normal in the same temps
Good flow into the coolant tank from the upper manifold

The Disco idles fine and keeps it's temp stable at a idle



Now here is the weird if I come off the highway and stop the temp does not drop by more than a degree or two, It will hold that until I move off then it drops.
Going up steep hills, 10% +, the temp climbs slowly but consistently, dropping rapidly to 174ish on the downhill.
As is expected the engine does increase in temp under load up smaller long hill climbs as well

I suspect it is the fan clutch although I did change it with my spare, Hayden 2991,both are 2991's. I did notice neither will spin cold, the fan is very very stiff. Do I have a bound-up fan clutch or something else?

 

You need to find some wood to knock on, you are taunting the LR gods. Go find something to actually work on. Leaking PS pump, sunroofs, subwoofer surrounds, oil leaks, whatever.

 

@Extinct Yea I know stop being OCD, today the aux fan decided to rejoin the living though.

 

If you are saying the electric fans in front of the A/C condenser (in front of the radiator) was not working, your experience sounds spot on.

Truck was generating heat at speeds >60 mph. Fan clutch + air flow kept coolant temp in check.

After generating heat you pull off highway where fan clutch is moving more slowly and air flow is negligible. It is no wonder your temp did not drop. I'd almost expect the temp to rise a bit given the 'thermal inertia' coming off the highway.

It is actually impressive that you can run your A/C at idle on a warm day and have no temp issue.

 

@WaltNYC Actually the cooling system works really well, but I spend a lot of time behind diesel Defenders doing slow steep hill climbs off road. So I get fair bit of heat build up, slow speed low rpms. And seeing as we rarely have cell service, when off roading I am a bit OCD about truck maintenance.

I suspect the A/C fan acting up did not help.

And yes I was amazed how well the Disco handled running A/C with no Aux fan as well.

 

Classic clutch fan life...

There's a thread linked in my sig about how to fix that very issue