2000 Disco II w/ 110K. Was driving on the freeway last night and noticed the temp light was on and the guage was bottomed out. Pulled over and sure enough she was overheating. Waited for it to cool off and filled the tank. Drove it slowly for about 10 minutes and the temp guage leveled out and have not had any problems in the last 24 hours. Have driven it about 10 miles since last night. Before i take it in to my local shop I was curious if anyone has a similar experience. Head gaskets and water pump replaced at 96K miles. No other vehicle issues..... except i do have the gurgling "air in the system" issue which i can cure by overflowing the bleed screw. Any help would be great.

 

First stop driving it before you toast the engine.
It will need to be bled and then pressure tested to find your leak. I would plan on a major job, with being that low on coolant, there is a good chance you have cracked a head, taken out the head gasket and or dropped a sleeve.
You have to check the fluid on these truck every couple of weeks or this is what will happen.
Let us know what you find.

 

Mine bottomed out due to tsat malfunction. replaced it and found a minor coolant leak and it is like new now.

 

Tonight on way home from airport My Disco II (2003) temp gauge started to rise - went to just under the redzone (on the white line below it).
Engine running fine however and I was close to a gas station so stopped for some petrol, cup of coffee....

Got back in after about 20 minutes, restarted the vehicle and temp gauge bottomed out - and overheat indicator lamp went RED. Pulled vehicle into parking and left it there.

Funny thing was I just took it to the shop like 3 days ago and they said it ran fine...I was complaining that the temp gauge was dancing around above the normal mid-range. The chief mechanic said he couldn't find anything but if it was anything he suspected a "lazy cooling thermostat"

I am hoping thats all it is

Ohh, before I forget - it was topped up with both cooland and oil after the visit to the shop - so the levels were apparently OK. Am not hearing any gurgling sounds from under the hood. Am not seeing any liquid leakage off the engine or elsewhere...

 

When temp gauge is unplugged from cable, or ECU can't see it, the ECU will turn on the warning light, and put gauge pointer in the basement. Unplug, inspect, and reseat temp sensor connector, it is between the alternator and AC compressor on top of the motor. You may just need a new sensor.

 

Yep - had some issues with that very sensor sometime last year and had it replaced. It was actually reporting that the vehicle was overheating when it was not.......
My mechanic told me that on my year disco this sensor is a nagging issue that crops up frequently....same on BMWs....

I think I will have them replace the thermostat none-the-less. At least then I know the whole system has been checked.
So far in 4 years I have replaced the master cyl for the brakes, 2 power window motor (all rear pax doors), 1 power lock, the entire engine was rebuilt, new water pump, new cooling reservoir and hoses, new oxy sensors (in fact they pop up warning lights more often than anything else on my disco)
new brakes, new disc brake rotors all around)

 

If you have a coolant leak and if you over heated running the gauge into the red, at some point air will be trapped around the temp sensor and you will get a cold signal.
You need to quit driving it till you can refill and bleed the engine when it is stone cold, then it needs to be pressure tested to find the actual leak that then has to be repaired before you toast the engine.

 

Just to be clear - when my temp gauge bottomed out and warning lamp came on. 1) I had no coolant leaking problems (that was something that had already been repaired with install of new reservoir and hoses 8 months prior, and a new temp sensor as well)
2) The vehicle had just come back from service 3 days prior and all fluids were topped up
3) The engine temp - as taken with laser thermometer showed all in the norm
4) The incident happened after tanking up on petrol, so I just parked it and left it at the station overnight.

Suspect was "lazy thermostat" or "defective sensor". Both were checked. Thermostsat was ok, but I had them replace it with a new one anyways.

Sensor was shorted and a trace of the wiring found that it had been re-routed by the dealership when they rebuilt the engine 24 months ago. And when they bolted things back on (like the aircon compressor, they pinched those rerouted wires, and over time they wore their shielding off to expose about 1/2 inch of wiring which was shorting against the engine block (aircon compressor actually). And this short - basically zapped the sensor - which caused the engine computer to raise the OVERTEMP alarm as a precaution - and since my vehicle is fitted with an emergency engine disable - the overtemp essentially triggered that.

Wiring replaced, heat shielded, sensor replaced, thermostat replaced. Cooling system flushed (just for the sake of being complete), pressure tested. No leaks, fluids topped up, vehicle tested - ALL GOOD
Total cost of 1 & 1/2 days inconvenience... and NZ$630. (about US$490)

 

Good, if that is the case, you got off easy.