I am having nearly this exact same problem. Jafir was really helpful in narrowing down what might be the problem but I still don't know what it might be.
Anytime it has been under a load recently the temp starts climbing, and I'm not even towing anything and its been cold over here.
Last time I climbed a hill, even for just a mile the temp went up to 220.

I have new head gaskets, new radiator, new fan clutch. I don't know what to do....let me know if you figure out whats wrong with yours.

 

I know this turned into a descusion about fans and not over heating but I have an issue where no matter what I do my 2000 disco to temp rises after about 30 minutes to the top of the white if I shut it down or just let it idle the temp goes back down. rhe top hoses get hard and the bottom is still spongy. Do these thermostats close up over a certain temp? I have heard that thermos are designed to do that to stop boiling water from going into the heater core.

As for fans the electric helps for low speed and cooling under load. As far as cfm's are concerned the reason you cannot find any factory data on the the stock fan cfm is because its a combination of the fan and fan housing and the convection they create together. The housing/cowl focus's the fans energy and creates a wind tunel behind the radiator thus pulling more air volume through a defined area. so in return you are getting more cooling where you need it. not to mension radiators prefer to have air pulled through them not pushed for all those the who didnt know.
For those who are towing and hauling remeber to do the math. if you are consistently pullyng eccess wait you should move into higher volume radiator and pump. don't forget a larger seperate transmision cooler. People often forget that all those cluthes and gears in our trannies generate allot of heat and that heat is transferred off via the trans fliud.

 

2000 disco is a D2 and you're posting in the D1 section

Sounds a little like a plugged up radiator to me.

 

Hello all,

I've just returned from a 1,950 mile trip to central CA pulling the trailer with no issues whatsoever and wanted to give an update to those that are having similar issues.

After I replaced the suspected faulty water pump, I replaced the coolant and really spent some time and attention to detail burping the system - using one drive-on ramp under the frt passenger wheel and getting the system warm.

Then I re-sealed both valve covers/rocker boxes and the intake plenum, as the valve covers had been seeping for some time and had gotten worse.

I double checked the electric Spal fan temperature settings and set the first one to come on at 185°F and the second one for 190°F. I want to get ahead of the cooling load when the tstat opens or stays open - not starting the fans when the radiator is already full of hot water and trying to catch up.

I've done several test runs - Phoenix at 95°F in stop and go traffic without the trailer - with the AC on it ran to 195° and stabilized, after turning the AC off it dropped to 185° in about 4 minutes. Pulling the trailer up to Flagstaff on I40 it topped out at 194° then dropped to its normal cruising temp of 177 - 183° at 85° ambient.

On our way to CA, we used I40 and hit 114° ambient temps after crossing the CO river and the long slow pull. I turned the AC off and had to slow to about 40 - 45mph but never went above 206°. Every time the road leveled off a bit the temps would start to drop. Once we were at the top, it returned to the normal temp of 185 - 188° with the AC on in 115° ambient heat. Climbing up Mt. Diablo from Walnut Creek was a very similar situation to our Kingman overheat, with a steep slow road that climbed over 2,000 ft in 95° temps. We saw 201° a couple of times, but nothing more.

I don't have a single smoking gun to point to, but think that the solution was a combination of factors - there was very possibly an air bubble in the top of the cooling system or intake manifold that just hadn't gotten worked out, along with the small intake leaks from the valve covers. Once I replaced those gaskets and resealed the intake plenum, there was a noticeable increase in useable power, along with a very pleasant increase in fuel mileage. Round trip to Albuquerque after the sealing resulted in a 13.5 mpg, up 1.5 mpg overall.

The Disco just turned 200K on this trip and maintained the speed limit with the exceptions of climbing hills, while getting 12.5 mpg and running very reasonable temperatures.