Hey everyone I'm brand new to this forum. I have a 99 Disco 2 that the obd2 scan tool shows that it is idling at 225*, when going out the road it shows 221*-222*, I am very suspicious of those readings because when I use a thermal thermometer on the temp sensor it reads 175-180*, the cylinder heads are running around 200*, you can hold the radiator hoses, nowhere on the engine shows signs of temps that are to high. the truck has a brand new engine, new heads, radiator, water pump, fan clutch, coolant tank,
180* thermostat, oil pump, interior and exterior fuse boxes just recently, among many other new parts. The cooling system has been bled as per about everyones directions, pulled up the overflow tank, removed the bleed screw from rad hose, filled slowly, and so on. My question is could the temp sensor be sending a bad reading, that is the only thing that I could think is going on. I did replace the temp sensor about a year ago with an aftermarket one. I saved this thing from going to the junk yard due to a cylinder sleeve slipping, and now it is back up and going so I wanna make
sure that it really is not running that hot. Any thoughts or ideas would be great. Thank Guys.

 

I would remove the coolant cap when safe; insert a candy thermometer and compare climbing readings with your scan tool for accuracy before risking a head gasket failure.

 

Sorry, I forgot to add that to the post. I used the candy thermometer that came with my thermal thermometer in the coolant, and it read 195*-200* when sitting and running, my scan tool showed 225*. Thank you for the reply

 

I had to change the temperature sensor on my old D2, and found one that fit and looked exactly the same, but read a lot higher. Nothing else had changed, and when I got hold of an OEM one everything went back to reading normally.
Since you're using an aftermarket sensor, I would suspect that there is where your problem lies.

 

Yeah, change the coolant temp sensor, they do occasionally go bad.