I have a 98 Disco with the 4.0 V8 and runs like a dream. Rebuilt the engine at 120k and now have 163k miles on it. I have pulled my 1000lb jet ski and my 3800lb boat and engine will not over heat. Turn the a/c on below 50mph and engine starts to get hot and so does the a/c. At an i dle a/c is hot and engine overheats. Here is what has been done. Water pump, thermostat, fan and clutch, temp sender, both electric fans have been replaced. Clean condenser and replaced radiator. I have also replaced radiator cap. This has stumped me. I put the low pressure guage on my a/c and it runs 60psi which is to high but compressor comes on and will freeze you out above 50mph. Any ideas? Condenser was not very bad and neither was the radiator but I left the radiator in the truck the six months I had the motor out and something may have made its way inside the old radiator but the new one did not make a difference. PLEASE HELP!!

 

Is your belt routed correctly?
It is very easy to put it on wrong on a DI.
It will look right,everything will turn, but it just wont turn fast enough.

http://www.roverparts.com/TechTips/s...g_defender.cfm

 

Took the laptop outside and double checked and the belt is on correctly.

 

Is the mechanical fan on the right way?
It can be revered and it wont pull air.

Mine had a similar issue, while off roading with the a/c on it would overheat.
Idling for 20 min or more with the a/c on and she would get hot, not overheat but get hot.
I replaced the fan clutch and now all is right with the world again.

 

I checked and made sure it was on right. Someone told me how to check it and I did and everything was good. I replaced the fan clutch not 5k miles ago. I don't understand.

 

This is making me scratch my head too.
I need to ponder this for a bit.
You have replaced everything so that is throwing me off.


Belt tension, is the belt good and tight?

 

belt tension is good and tight. This thing has me stumped as well and it gets pretty hot here so I need a/c. If I am going 70 and am close behind someone with my a/c on the engine will start to get hot but usually at 65-70 the temp stays right.

 

So your not getting good air flow or the radiator is restricted.

Since the a/c stops being cold at slower speeds too I would say the air flow through the radiator and condenser is to low.
Have you cleaned the fins on them with a garden hose?
Is it really dusty where you live? (location in your info helps)
Leaves, a birds nest, mouse nest, etc. could all cause problems.

 

Brand new radiator as in I replaced it yesterday. Cleaned out condenser but it wasn't bad at all.

 

Fins on condenser or radiator smashed or dented? A tool like this works wonders on damaged fins (as long as you have patience).http://www.amazon.com/Interdynamics-.../dp/B002G1UNJE