So here I've been going bananas trying to figure out if my Disco is overheating. On the temperature gauge that's on the instrument cluster shows red, the Ultra Gauge plugged into the OBD2 port shows a fluctuating temperature of 253.3 ° F to the highest I've seen was 284.0 ° F. Now I know what you gents are or probably crapping your pants as you're reading this, but I changed all the cooling components except the radiator, and top hose. Head gaskets done back in 2017. I did the engine block test, nothing the liquid was blue. I checked the dipstick, nothing it's black. I drained a bit of oil from the oil pan, nothing it's black. I bled or so I thought I did, had it towed to Firestone and they did the block test and radiator pressure test nothing. Everything came back negative, they used a temp gun and nothing was overheating, they even took a temperature reading using a digital thermometer that they stuck in the coolant, and nothing. The temperature read between 130-190° F as far as what they said. They let it cool down for an hour and went back to check it out. They said that temperature gauge was at the half way mark of the gauge on the instrument cluster. So I have no idea what it really is, they reassured me that it was drivable but just had to change the temperature sensor or gauge. I gotta be honest here guys, looking at the UG measure in at 280.4 °F had my butt clenching lol also the needle on the gauge shows it falling dead with the UG measuring at 280.4 °F and then when I drive it drops down to 258.3 °F not like that makes a difference or whatever, when that happens the needle shoots all the way to red. Lol I'm so baffled. What I'm thinking is the either the instrument cluster is messed up, the ECU or ECM is messed up or something electrical. The reason why I say it's either ECU or ECM (not sure which one controls the Dash) is because the odometer blinks while displaying the mileage. I'll post pics of what I mean.

 

Why are you thinking it's the gauge, the ECU, or the BCU, but not the temperature sensor(s) itself?
The dashboard gauge is basically a three-position idiot display (cold-warm-overheated) so it's not really telling you anything, but the Ultragauge certainly is. And if that's not lining up with an independent temperature check, why not start with the obvious possibility first?

 

Because as I stated above, I changed all cooling components including the temp sensor. Which is a brand new one from AB. And where exactly does the ultraguage get it's information from? The OBD2 port right, so maybe something is sending a faulty signal that's between the coolant sensor to the dash board. I'm not pulling anything out of my *** but if several people looked at it and physically confirmed that there isn't any coolant leaking into the block then it's probably something electrical.

 

if the odometer is blinking there is definitely something wrong. pretty sure that means the mileage on the odometer doesn't match the BCM. did the instrument cluster get replaced at some point?

i would get a new temp sensor also and pop that in. i know you already replaced it but if the UltraGauge is reading too high then it is getting false information from somewhere. assuming the truck is actually not running hot per your other tests.

 

Temperature sensors are electrical.
I bought one from AB that was supposed to be the correct one, and it was for a different truck. It read substantially higher than it was supposed to.

 

Ah yes the BCM, I apologise. I wasn't sure which part controlled the instrument cluster. And no I did not replace it, but there was a leak on the driver side upper windshield where rain water would drip down on the steering wheel and water making its way down into the cluster and possibly the fuse box. The leak has been fixed but the damage has been done. Also the windshield cowl was old and broken when I originally bought the disco back in 2016. I didn't know at the time that water would leak into the passenger side wall and floor. The part has been replaced but damage probably already done as well. I mean I'll change it but I don't know if that'll make a difference because when I had the HG done I also changed all of the cooling parts including the temperature sensor.

 

Well I took the part number off the Rover North website that was specific for the Disco 2 and matched it up to one on AB but maybe it's a faulty one. I already called AB and they are sending one out.

 

Why did you change the original?

 

I didn't, the mechanic shop did. I may have misspoke. But the one I have on now is a genuine sensor

 

Sounds like temp sensor to me as well.

(my thought is that if your temp was really as high as 284 degrees for any length of time it's very likely the expansion tank would blow, or something else would seem amiss, coolant overflowing out the overflow tube, hoses bursting, the weak link would give)