Before you install your new rad, make sure you flush out all the old problematic coolant from your engine and heater core so you don’t clog up your new rad right away.

 

I know it has been mentioned above, but do the inline thermostat. The best money you can spend on these trucks. Espcially given you will have everything apart. Also worth doing the overflow tube, its plastic and will likely break. People have replace them with a rubber hose. Needs to be chemical resistant if you go that route. Obviously if there are any buldged hoses I would replace those also, but I am sure you have considered that. Maybe a new tank, but is up to you. Again for the money and peace of mind it is worth doing.

The cooling system is the weak point on Discos and the above basically shield you from any reasonabvle failure. Nothing worse than breaking down on the side of the road.

 

My recipe for cooling success in AZ (100 - 115 ambient at times):

- Extinct's inline kit (single biggest improvement)
- Flowkooler water pump
- Ultraguage for monitoring (alarm set for 212)
- GM fan and clutch (Chevy Blazer, I think)
- Nissens radiator

In the winter/spring/fall (50 - 80's ambient) my '03 runs around 177 - 188.
In the summer it runs 188 - 205 in most cases with the A/C on.

If I'm going up a steep grade on a hot day, I just hit the "Econ" button on the A/C until I'm done with the climb and temps settle back down.

My Disco currently has 98,000 miles on original head gaskets.

 

I’m on in-line mod. Running @210 in traffic in Central Texas. I’m fine with it.

as with mentioned earlier, 220 is oem operating temp.
The issue is the gauge doesn’t show anything for at least 20 more degrees so by the time you notice and shut it down, you’ve most likely blown a hg.

Lots of cars are like this btw. It’s not just Rover. We catch flack because these truck were kinda “expensive” back then and the 4.0 and 4.6 engines just leak, and are underpowered

 

I was doing some dev work on the coil kit and dropped a screw down the intake of one of my recent acquisistions (dumb rookie move) and had to take the lower intake off. I never get that far and don't do HG. When I got the heads off it was obvious they were the original HG's - 216k on the clock. I think yours will likely surpass that with your setup if you keep it that long.

 

i flushed it with the old radiator when I used the flushing agent and 8 gallons of distilled and again before I installed the new one

new radiator installed and it didn’t change anything

still hits 215-217 with the AC on at 70 mph

so either that is normal for my rig or it’s something besides the radiator and an in-line isn’t making a difference

 

any other ideas to try next? I installed a new radiator and still have the same thing happening

What’s left after new radiator and in-line? Reservoir and hoses are 4 years and 8k miles old. Water pump is the same age.

i run a 2” lift and winch, roof rack - and it’s high 80s in Texas now - so am I chasing a ghost trying to fix my temp hitting 215-217 at 70+mph with the AC on?

 

Since you did the inline take the thermostat out and see what your temps are - those are high for a 180 and good cooling system.

I only hit 190 -196 in the 80's at 70.

 

This D2 cooling system will hold 100 degrees over ambient at 70 on relatively flat ground on a stock truck. So you are high 80s so lets call that 190 temp. Add winch, lift, tires, and roof rack and you have added 10 degrees of cooling load so yours should be in the 200 degree range normally. Lets see what it does with no thermostat element at all. BTW, we have had a forum member put a brand new radiator in that did not flow correctly and had similar results to you, so would not rule that out. What part of Texas are you in?

 

Ft Worth

with no thermostat and AC running, I ran around 200-204 at 70 mph and 210 at 80 mph hitting 212 a few times tonight but never going higher