Have an interesting situation with a new to me 99 D2. Ultragauge shows coolant temp at 250 when actual temp is about 180. Confirmed with IR and 180 tstat opening. The dummy gauge is buried in the red upon start up and moves down to normal as the rig comes up to temp.

Just wondering if anyone has had this issue. I assume there’s a short somewhere in the wiring. I have replaced the sensor, no change. Also worth noting, the gauge cluster appears to be out of a later disco. If I remember correctly there are different sensors for the 4.6 vs the 4.0. The condenser fan kicks on when the sensor reads 210 so the computer believes this to be the actual temp. However, the red overheat light doesn’t kick on at any point. Not sure how this affects fuel trim etc. Any help or insight appreciated

 

Hi.
A 180F thermostat does not mean at all, that the coolant temperature will be 180F. What does 'a short' mean to you ? The red overheat light and the pointer are LandRover temperature adorns for the dash instruments. Check the ultragauge on another vehicle. What is the dummy gauge ? The adorn thermometer on the dash ? --- with red, white, blue bands ? If yes, ignore it. Has no scale, does nothing, tells nothing.

 

I'm assuming he means he's using IR on the coolant lines around the thermostat to verify operating temp.

If this were me I'd immediately pull a temp sensor off of my parts rover and toss it on the offending rig.

I've not had a Rover temp sensors fail before but they are common failure enough on the VW TDI engines I run that we replace them and the coolant TEE block on the back of the head any time we are back for pretty much any type of repair work.

On many newer vehicles there are two temp sensors and a CEL will be thrown if one of them malfunctions or if a thermostat sticks open preventing the engine from reaching normal running temp. The disco isn't that smart which is one reason why these are usually simple to work on

I'm also a big fan of adding a secondary temp gauge inline on the top coolant hose or in the housing of a thermostat upgrade. This gives you a secondary temp source to check along with the ECU reading.

Like many vehicles, the in dash temp gauge is a dummy gauge. Many times once it's moved beyond the normal spot you're already in trouble.

The engineers did this because they didn't want service departments blown up with phone calls because it's only hitting 175 on a 20 degree day or hitting 210 on a 95 degree day.

 

The coolant temp seems to float between 174 and 185, same as my other D2. The ultragauge came out of my other rig and worked fine. It’s just really hard to drive around with 250 showing as I’m sure anyone on this forum could appreciate. With two different sensors acting exactly the same I would assume the problem is either in the wiring for the sensor (rubbed through in the loom or poor ground) or in the gauge cluster. As I stated, the cluster appears to be out of an 03 or 04 which had a different style temp sensor. I’d just like to have the ultragauge and ecu see correct readings. And to put the 40 amp fuse back in for the condenser fan.

 

The plot thinkens if you've mixed and matched clusters/sensors.

I've interchanged many parts from our 03 parts rig to the 99 DD but those parts are not one of them

 

Yeah whoever installed the updated cluster also blotted out the amigo lights so that’s on the list. May just pick up a correct one and see if that changes anything since it needs to be swapped anyway

 

Unlikely it is the cluster, the years are interchangeable for the cluster. Likely a bad sensor but if you replaced it and it does the same thing then maybe it is wiring. have you chased that down yet?

 

I was worried that was the case, thank you Extinct. Aside from cleaning the braided ground I haven’t messed with the wiring. It does read -40 unplugged which I’ve read is the normal. I was really hoping to avoid chasing that wire all the way back. I didn’t notice any corrosion on either end so I suppose I’ll check resistance. A 70 degree discrepancy is pretty wild

 

There is some data in the RAVE on the sensor resistance and characteristics.

 

I have had trouble finding an accurate sensor for my P38. Perhaps this is similar.

All 'actual' temps are IR gun readings from the output tube of the manifold toward the radiator. So while the IR gun may not be 100% accurate, I believe it is relatively consistent.

- Genuine Land Rover.. seems to read 7-10 degree low (obd = 175, actual = 185) ... the gauge on the cluster functions
- All Makes (AB) ... seems to read 10-15 degree hi... (obd = 205, actual = 190) .. the gauge on the cluster does NOT function
- Walker (rock auto) .... seems to read 20-25 hi (obd = 210, actual 185) .... no gauge

The main 'problem' with using the genuine sensor is that on the P38 (and maybe the D2) the SAI system checks the difference in temp between the intake manifold and the bottom of the radiator. If the difference is too small the computer interprets that as the thermostat not opening. It then throws a code P1667.

So the developing narrative is that temp sensors are wildly variable.