840 Erratic Temp Gauge

[Wuffer]

We have near 120 8's on the BC 8's Registry. Most are early 850's and after 11+ years of ownership and parting out 8 of them, I am pretty comfortable troubleshooting and repairing the V12's. Many local owners bring their cars to me to figure out. The currect issue I am inquiring about is an erratic temp gauge on a 97 840Ci. Works sometimes, sometimes not. I suspect flaky engine temp sensor but no idea where said temp sensor is located on the V8. Is it the sensor on the side of the rad that sends info to the gauge or some other sensor? Guidance please.

[DanB]

Per Timm http://forums.bimmerforums.com/forum...ge-going-crazy

[m6bigdog]

passenger side of engine, on the coolant crossover manifold at the rear of the head and near E-box.
Edit reply:
I found a better image of the location - B6232 is the Instrument Cluster temp sensor
B6236 is the DME temp sensor

[Timm]

Yes, the 840ci never got the temperature-mapped thermostat that the E38 got with the same engine, so the coolant sensor stayed in the same place as the E32 with the M60 - on the coolant cross-over casting.

[Wuffer]

Rod, what your pics show is an M60 engine with temp sensors in the coolant tube at the back of the engine. The M62 in the 97 does not have sensors there, just plugs. I am thinking that the only coolant temp sensor on the M62 is the one on the top of the waterpump described in the ETK as "Double Temperature Switch 13 62 1 703 993".
Dan, the temp gauge either works (shows needle at 12 o'clock) or doesnt work at all. Never jumps around or goes into the red erratically.
So the question is... is there any other sensor for water temp that communicates with the Temp Gauge?
Thanks for the input thus far.

[revtor]

I am thinking that the only coolant temp sensor on the M62 is the one on the top of the waterpump described in the ETK as "Double Temperature Switch 13 62 1 703 993".

That's indeed the temperature sensor you are looking for.

[DanB]

I didn't remember any switches back there on my M62... My guess would be the "double switch" on the thermostat as well.

As for the signal on/off, sounds like a loose connection or a bad solder joint on the instrument cluster. When it's not working at all, maybe try a couple of different things: a) perform the instrument cluster test: https://www.youtube.com/watch?v=B7EL3raLW5A b) tap into the wiring harness at the junction box on top of the engine and see if you can pull signal from the temp sensor wires. c) unplug the instrument cluster and see if there's signal reaching all + leads to the plug.

[m6bigdog]

Rod, what your pics show is an M60 engine....

I stand corrected. Sorry for the wild goose chase.

[BMWNTHZST]

I just checked the VIN on my '97 840CI and it would appear part number 13621703993 is the correct one (Double Temp Switch) found on the top of the water pump.

[Wuffer]

Double Temp Switch ordered - will report on result after installation.

[IcemanBHE]

You need to check over the plug and wiring at the sensor. They have been known to weep, and wick up the loom, shorting the DME. Just look it over.

[Wuffer]

10-4!

[Hyper]

For those who simply refuse to get behind an M62...



Actually a TUB example, so up front, the thermostat heater connection exists over on the left side of the pump manifold, and the coolant temp sensor is still on the right.




An insider tip...

[BMWNTHZST]

Excellent!

[Wuffer]

To close out this thread, double temp switch was installed and problem resolved.

[sevenit]

Hello everyone. Having the same temperature gauge problem. It's all over the place and my 1995 840CI (150,000) is running rich. Changed MAF, all new coils, new spark plugs, new fuel injectors, checked for vacuum leaks, new valley pan gasket, new PCV, cleaned and tested idle control valve, compression tests normal, new air filter, replaced fuel pressure regulator, replaced both temp sensors, Timm's intake manifold fix (Thanks Timm, also having it painted the same color as yours!), reconditioned carbon canister, new cats, new 02 Sensors, new fuel pump and filters and it's still running too rich to pass California Smog test! It runs pretty good, lots of power, idles at 650 but a bit bumpy at idle, but smooths out as soon as it revs up a little. Hard starts. 3 times to start. Ugh! Out of options and money! Help, please! My Dog and I have prayed over it, still no luck. And the worst of all this is now my Dog is exhausted and looks at me with little faith and complete disgust in his eyes.

[Timm]

If you haven't got them already - you need diagnostics! With diagnostics you can find out if the engine really is running rich, O2 sensors (especially new ones) don't lie as a rule and diagnostics will show exactly what they are reading - all explained here (I know it is a bit long-winded, but stick with it and it will all make sense):



.....and here:

https://www.meeknet.co.uk/E38/Diagnostics.htm