Hi all,
I have an 01 Disco, it runs really hot when I have the A/C on after about 30-45 minutes. If I turn on the heat and defroster it will come down to normal tempature. It has not overheated, but it goes up to the top white line and then I'll turn on the defroster and it will come back down to the middle temp setting.
In the past 6 months I have had the head gaskets replaced, just had a new thermastat installed, new lower A/C hose and today I had the fan clutch installed.
I am out of ideas, so any help would be greatly appreciated.
Thanks,
Lee.

 

Electric fan not working or stops working is my first guess.
You dont need to turn the heat on, just turn the a/c off and the engine temp will drop.

Next time it happens leave the a/c on, pull over and get out of the truck and listen for the electric fan behind the grill.

 

1) Radiator plugged. New radiator.
2) Electric fan. Can you hear it with the A/C on? It has quite a high pitched roar
3) Fan clutch. When your temp are high, you should hear the big fan pulling air thru the radiator on a hot hot day with your engine temps high.
If not, fan clutch may need replaced..

4) Check the routing of the serpentine belt. May be on the wrong way.
I have heard this is possible.

It is 106 degrees in Boulder, CO today.
I am going to scan my temps and see what they are out and about.

 

A radiator that is sludged will look OK on outside, but check with an infrared thermometer, top to bottom of the fins. Should be close to 10 degrees change. If a good deal more, lower rows could be sludged and low water flow.

If electric fan is not working, normally you will overheat when slow or parked. When it is off you should be able to spin the blade with a screw driver. If it is binding up, the fuse has probably blown and you need a new fan.

Serpantine belt route if clutch just replaced.

 

Denver was ridiculous today. My Ultra-Gauge II alarm went off at 230F as I was driving through downtown. I pulled over in the shade turned off the ac and immediately the temp started back down from 234F and stabilized at 217F , as compared to the usual 188.6F. The electric fan sounded like an old hamster wheel.

The stock gauge of course barely moved from the center.

I went to the gym to get my swim-on and let 'er cool off a bit. I drove around a bit, in town, on the freeway, ac on, ac off. I'm more of a windows-down guy usually, but 105F ?!!! Idling and driving around town, without ac, the temp stayed nice and low (185-190.)

On the freeway with the ac off it stayed in the green (190-194.) Switch the ac on and it jumped up (200-204.) I got off the freeway and left the ac running. Temp crept up to 210F before the light changed. Then stayed there all most of the two miles home before settling back around 202F. Then I idled until it reached 220F and them I flipped off the sc and let it idle back down.

I've determined my electric fan is probably knocking on death's door and my fan clutch doesn't seem to be engaging as it spun fairly freely (though sluggish) with an engine temp of 215F. Plus with 84K on the clock, it's probably time for a water pump.

Now time to research the cheapest/best replacement options!

 

You can check fan clutch by spinning it with truck off, cold and hot. Should not go more than 1 revolution when released, should feel like peanut butter inside. If it freewheels, time for clutch. Radiator could use a flush. Radiator fins could be clogged with mud and leaves. If considering water pump, there are aftermaket ones that push more water, have a large bronze impeller (BP Utah), and don't forget the 82 C thermostat with "soft spring".

 

I was passing through Denver today as well, My ultra gauge spiked to 210 with the a/c on but stabilized there. It was a bloody nightmare driving here today!
Good luck!

 

Yeah, tomorrow is supposed to be slightly less brutal. After some more reading looking at others' numbers I think maybe I was dealing with a little fluke. The fan clutch seems fine, I was a bit confused about how "locked" it is when hot and the engine isn't running. It definitely roars with engine revs more when hot and doesn't spin more than an eighth of a rotation after a good spin by hand.

I do think I'll fit a new electric fan. Sounds like the bearings are about to give it up. And I think maybe a tripmtomthe ac specialist might be in order. Perhaps my ac won't have to work so hard to maintain the set temp if it's properly serviced.

 

The fan clutch is full of silicone fluid, separated by two grooved discs. When cold, the fluid has pooled to one side, and will roar on start up, until fluid moves around and warms up slightly, then it decouples to about 20% power. When it heats up enough on the front plate of the fan, it engages to higher power, like 70 -90 %. Some clutch designs have a on/off thermal valve that does this, many are also variable speed, so it slowly gors to higher coupling and back. So you fan clutch sounds good.

Elecric fan good idea before it goes. You can use aftermarket generic, used one, or buy on line, forget the dealership. There is no thermal sensor, the ECU monitors the same spot as the Ultra Gauge and decides when to turn it on.

AC freon (refrigerant levels) can also make a difference, and head pressure of compressor (high side) really drops when electric fan is on, so having both working great would be a plus.

You would think a truck made for bouncing in Borneo could have mastered the soccer mom waiting for 45 minutes overheat issue..