I have an 02 Disco and as the weather has warmed up recently, I've had problems with it running hot, so I changed the thermostat and flushed and filled the system with new coolant. I even added a bottle of water wetter, and bled the system of air. My problem is that I am still overheating at highway speeds. After about ten minutes of solid highway driving, my temp creeps up to the point that the warning light comes on. Around town it does fine all day, until I get on the highway and then it overheats. Can someone please help? We are driving to the Carolinas this weekend and I need to get this fixed ASAP!

 

......and you are losing coolant, right?

You have a bad head gasket.

 

Clogged radiator.

 

Clogged radiator would be my guess. If you pull the radiator cap do you see coolent returning through the small tube at the top?

 

I am not losing coolant, and yes when I remove the cap, I see water streaming back in.

 

What could I do to get my radiator unclogged?

 

At highway speeds, only the radiator, water pump, and thermostat have an impact. With it running OK at low speeds and engine load around town, you probably have eliminated the thermostat (which determines how cold the engine will be at normal operating range), and the water pump (bad water pumps tend to be bad at all speeds). The fan is too small to make an impact at freeway speed. Try holding a pizza box out the window at 65 mph, you will see how much air is being pushed against the radiator. You will notice that large construction equipment has giant radiators and huge fans - because they don't go at high speeds and must make their own airflow. Trash between the radiator and condenser is probably not the issue, or you would have overheating at low speed as well. Flush really good with a chemical flush, inspect through the top hole for calcium build up on the tubes. If there is some showing on the end, it is probably along the entire length of the tubes as well. This reduces the cross section of the tubes and changes the heat exchange rate of the radiator. All those little calcium crevices just love to plug up with the head gasket or radiator stop leak "cures" that are sold in bottles. Years of no coolant change and/or failure to use distilled water adds to the problem. If you have an IR point and read thermometer, check the radiator with engine warmed up, my indy radiator guy says a good radiator will be within 10 degrees top to bottom. If you want a shop to work on the radiator, look for an indy one, small, and if possible out near the farm country, where they have to work on all size tractor and equipment radiators; and they don't charge by the MSRP of your truck. Remove it yourself in 10 minutes and take it in to save $. The indy shop I use charges $65 to boil and rod out a Disco 1 radiator, the big shop in town wanted $150 to start...

 

What Savannah said.
Contrary to popular belief engines fans are for low speeds and idling only, they do nothing while driving over 40mph or so.
And the electric fans in front of the radiator are for the a/c only, they do nothing to cool the engine and they shut off once you have reached 35mph.

 

OK, so I've ordered a coolant temp sensor and a new radiator. They should be here Wednesday, so I'll pray that this is the fix, as I've tried everything else. I did forget to mention one thing, though. When the motor gets overheated, you can here a loud ticking sound coming from it at idle. It actually sounds like a stuck lifter. What could this be? I am actually worried that I could have a bad head gasket. I didn't realize these had such a high failure rate! If my heads and/or head gaskets were bad, though, shouldn't I be losing coolant, or seeing the telltale signs such as coolant in my oil, etc? By the way, should I be seeing a steady stream of coolant returning into the reservoir with the cap off, or not? Ahhhh!!! Banging my head off the wall!

 

I'm getting the popcorn...this ought to be good. Map out indie LR shops as mentioned in an earlier thread and put DiscoMike on speed dial on your cell. HGs are easy...slipped liner...not so good. Do a search and pray to the LR gods...