[torbjorn123]

So, my p38 has some wierd issues, reading the temp with diagnostics it shows 120 degrees at running temperature, gauge is fine, then read gearbox ecu engine temp and it shows 80 degrees, as I understand this info comes from the engine ecu through can bus. Also the ac fans are triggered on by engine ecu. Replaced the temp sensor, same readings but now the gauge reads just above the blue area. Tried another diagnostic, same ecu reading, tried another engine ecu, still the same readings, tried another temp sensor, still the same. What could be causing this? Also have a text in message centre showing air bag fault at startup, but no fault codes or aurbag light.. Also noticed the lights in the message centere is flashing after shutting down the car, but while running it is stable.. any ideas?

 

[DaGlitch]

Sound like your thermostat is stuck open?

 

[torbjorn123]

Engine gets its running temperature fine, and also both the thermostat and water pump is new

 

[Dtoyne]

I must admit, if my engine was showing a running temp of 120 degrees I would be very, very concerned. That is way too high for normal running. Most are around 88 (GEMS) and 98 (Thor). If your 120 is actually accurate, you have some serious issues.

 

[torbjorn123]

No, 120 degrees is not acurate, the 80 degrees read from gearbox ecu is more acurate, running temp is fine on the car, 98 sounds high on the thor as the thermostat is 82 degrees.

 

[Escape]

I fear some details are lost in translation or just not clear

• the temp gauge on the dash shows correct temperature?
• which diagnostics are you using to get the reading of 120°C?
• why are you looking at the gearbox ECU?
• when do the fans come on? And do they also come on with AC off?
• do you have any reason to suspect the engine isn't running at the correct temperature?

My guess is the diagnostics you're using are not reading the ECU correctly.

As for your last remark, GEMS and Thor use the same thermostat, that starts to open at 82°C. But still it is common knowledge (or assumed) the Bosch runs at higher temperature? The pipework is the only difference, not sure if that would be enough, even with an external thermostat.

 

[Richard_G]

I'm also not clear on the problem. No idea why but my experience with a number of different cars is that the GEMS run cooler than the Thor. With the cooling system in good condition GEMS tend to run in the mid to high 80's while the Thor is usually 5-10 degrees hotter, but certainly not at 120 degrees. Even though the coolant will boil at a higher temperature when under pressure, that is still on the verge of boiling. Gearbox temperature has nothing to do with engine temperature, that will vary with load. With a replacement sensor (assuming a good one and not some cheap Chinese Amazon copy) I also suspect a misread from diagnostics.

 

[torbjorn123]

Maybe I wasnt clear, Ill try to list it:
Checked the engine temperature with Nanocom after I replaced the water pump, when its around 0 degrees outside and engine cold it shows +30 degrees and at running temperature it shows 120 degrees. Also tried a couple of other diagnostics from Topdon borrowed from work, all showing the same temperature. Gauge is in the middle showing normal temp. Reading engine
temp from transmission ecu with diagnostics shows 80 degress wich is correct.
Replaced the tempsensor on the engine (Thor) Still same ecu readings, but gauge only moves up to just above the blue area.
Replaced the Engine ecu, still the same
Replaced yet another temp sensor, still the same.

The AC fans is triggered on by the engine ecu at 99 degrees. This can be read with diagnostics and this reading is ECU status, and has nothing to do with the AC system
This means that the ECU actually believes the car is overheating, altough it is not.

 

[Richard_G]

If the sensor and ECM have been replaced, you must have a problem with the wiring for it to show +30 degrees on a cold engine when ambient is at 0 degrees. When the car has been left the coolant temperature when cold will be the same, or very slightly, 1 or 2 degrees, higher. The sensor is resistive and fed with a 5V supply from the ECM so the output voltage will fall as the temperature rises as per the following chart:

The sensor has two sensors in the one body, one to drive the dashboard gauge and the other for the ECM. If the wires have been crossed you will get erroneous readings as the two internal sensors have different characteristics.

 

[95classiclwb]

some time in the past I had a similar issue on a 2k discovery, it ended being a defective aftermarket replacement sensor.
while testing and engine running, I unplugged sensor and fans stopped (they would run upon engine startup).
finally, I procured a temp sensor from dealer and issue solved.
thor is designed to run about 30 deg Fahrenheit warmer than gems, this is for emissions reasons. while gems will run at 190 to 195 deg F Thor will run at 210 to 220 F yes almost boiling point.
gems uses thermostat mounted on top water jacket, Thor is at bottom of radiator and it is a heart valve style. totally different.

 

[Richard_G]

gems uses thermostat mounted on top water jacket, Thor is at bottom of radiator and it is a heart valve style. totally different.

No it doesn't, they both use the same heart valve style thermostat mounted in the same place. Some misguided people have been known to put a second thermostat in the top hose connection and then wonder why their car runs hotter.

 

[95classiclwb]

ok

 

[Richard_G]

The thermostat housing shaped piece at the top hose is a legacy from the 14CUX engine used in the Classic which did have the thermostat there but should be left empty on a P38.

 

[95classiclwb]

it has been some 13 or so yrs since I last worked on a customer's rover, by then the early v8's had been mostly phased out of production, there are so many details which skip me. I admit.

The thermostat housing shaped piece at the top hose is a legacy from the 14CUX engine used in the Classic which did have the thermostat there but should be left empty on a P38.

 

[pwood999]

+1 on the sensor or wiring being duff. Compare the ambient temp to the block itself first thing in the morning. If they are both at or near 0-degC, then so should the coolant & sensor readings.

 

[torbjorn123]

Latest update, checked all the wires yesterday, cleaned out some connectors and put the old genuine sensor back in and voila the temperature gauge started working as it should and checked the ecu temp after driving for a while and it was 92 degrees, perfect! So, just ordered a new GENUINE sensor

 

[torbjorn123]

But, while reading temp from engine ecu shows 92 degrees, reading the engine temp from the gearbox ecu showed 56 degrees, so something is wierd
Any ideas on the airbag fault message in dash without any fault codes or airbag lamp`?

 

[95classiclwb]

transmission temp will vary widely from engine reading, at idle it may be slightly above room temp but less than half of engine temp, as you drive the temp will increase but will never equalize the engine's. if you tow, specially a heavy load on uphill grade, the trans may go into protect mode and extend shift points to lower temps, the warning will come on only after threshold has been exceeded.

the lower the oil temp in your trans , the longer it will last.

see ashcroft transmission's website, they are rover trans premiere service shop and they have lots of good info, give them a call and chat with them about your concerns, they will have a response that will ease your worries.

 

[Richard_G]

But, while reading temp from engine ecu shows 92 degrees, reading the engine temp from the gearbox ecu showed 56 degrees, so something is wierd

Quite normal, as 95classiclwb says, gearbox temperature and engine temperature have no bearing on each other. Gearbox temperature will rise while you are driving and vary with load but will never get as hot as the engine, it doesn't have petrol being ignited inside it many times a second.

Any ideas on the airbag fault message in dash without any fault codes or airbag lamp`?

My spare car does that sometimes if it hasn't been started for a couple of weeks or so. Switch off, restart and it goes away. I've always put it down to low battery voltage while cranking as an alternative to the gearbox fault which will come up under the exact same conditions.