Older Bmw: very strange Temp Gauge problem

[InYaMooey]

Can anyone help in this one ?

BMW E39 M62 Engine (not that I think that is really relevant)

Problem is the Dash Temperature gauge goes to maximum, this is after the needle gets to about 10.30 position then straight to the red
Now the strange thing, it only happens when the ambient temperature is down to single figures !! Works perfectly all summer!!

New sender, plug contacts cleaned and cable looks ok before disappearing into the loom ..

Any ideas on this one? The ambient temperature part is really frustrating me.

Plus I’m st with electrickery

Thanks in advance

Edited by InYaMooey on Friday 25th September 18:26

[InYaMooey]

Thanks all,

GreenV8S said:

What temperature does 'about 10:30 position' represent?

Hi Peter, normally anywhere between here (see pic) and 12:00 is when it decides it likes the red zone sharpish (as in straight over) Huff has put some numbers up.

stevieturbo said:

Said lots about electrickery .

Will have to get a mate on this as im good with Oily,Rusty or wet bits not so much the devils invisible magic

I FORGOT TO SAY The other problem is it's intermittent but only happens at lower ambient temps sometimes <12 but more so <10c

It does occasionally revert to 12:00 when driving but not very often (no noticeable road bumps or thumping the dash )

And ignition on/off doesn't solve the problem.

njw1 said:

I had exactly the same problem.... disconnect the battery ...

Did this a few times last year and didn't help now have years worth of 25mpg average that i'd rather not scrub

Huff said:

Sound like you've something wrong with a sender, or wiring.

The temp gauge first quarter mark is about 60dgC , BTW, whether e39 6 or 8 cyl. It's the point at which the interior vent /demist fan system turns-on properly ( -it is programmed not to before that, to ensure a speedy warm-up!)

New sender, i have a fear that it is wiring

Doesn't coincide with fans as far as i can tell.

E-bmw said:

You say "works perfectly all summer" is this the same as worked fine until I put the heater on?

Very much not ..

Edited Yes i have new pads ready to go on

Edited by InYaMooey on Saturday 26th September 18:46

[InYaMooey]

Penelope Stopit said:

Have a hunch it's a fault within the instrument cluster, but.....

What does the gauge show when the engine is running and the temperature sensor is disconnected, if the gauge swings over to hot there is a possibility that a cable is going open circuit between sender and gauge.

Very much doubt that the above is the fault as a cable will go open or short circuit with vibration more so than it would with a variation in temperature (summer/winter)

Instrument cluster fault is the favourite, there could be a dry joint at the cluster circuit board that is breaking down when a certain ammount of current is flowing through it during colder outside temperatures

There could be an internal fault in the cluster that can't be seen (electronic or connection)

Ignition OFF needle hard left
Ignition ON Cold engine needle primes to first white bar this is the same with the sensor plugged in or not !
Warm engine sensor unplugged needle returns to first white bar.

I also think it might be a cluster fault so will pull it and re seat the plugs/wiggle the wires (I can manage that much electrickery )


Megaflow/Buggalugs
4 pins in the sensor/plug all cleaned and even when the plug is not fully seated giving a reading back to the gauge.

I have INPA (used for sorting the rear SLS and a few other bits) but every time i threaten the car with it typically the gauge isn't/stops playing up. As i said it is intermittent and not appearing so often at the current temp 13deg

Although it did hard over this morning but by the time id got home, you guessed it, vertical needle

Pete/bugga
Yep Stevie, 2 sensors, this one, near the Stat at the top front of engine, the ECU/Fan etc sensor is on the lower rad outlet.

Thanks again all.

[InYaMooey]

InYaMooey said:

Ignition OFF needle hard left
Ignition ON Cold engine needle primes to first white bar this is the same with the sensor plugged in or not !
Warm engine sensor unplugged needle returns to first white bar.

i will try and catch it when needle is far right and if any difference or back to first white bar or hard left (this will be slightly difficult to judge as its only a few mm)

Edited to add: Pulled sensor plug when needle hard right/in red and stayed in that position

Plugged back in and sill red but returned central a few minutes later (not surprised by this with it being intermittent and borderline ambient 12c not lower)

Edited by InYaMooey on Sunday 27th September 17:51

[InYaMooey]

Penelope Stopit said:

Cluster fault is now the favourite after your diagnostics unless the temperature sensor sends a signal to the DME ECU which then sends a signal to the cluster, doubtful but can't get hold of a diagram to be sure

Could unplug the ECU to prove if it does send a signal to the gauge

Thank you for going above and beyond

My favorite was also cluster (but see follow up below)

Really don't/didn't (see below) want to start messing with ECU

GreenV8S said:

I wouldn't be surprised if you found a wire with damaged insulation.

Thanks Peter (We've been in discussion before on high power V8 TVRs under a different name )

I think this might be nail head situation.

again see below

buggalugs said:

According to Figure 14 here, if you jump pins 1 and 2 together the guage should go max hot, which gives you somewhere to start from in testing.

https://www.pelicanparts.com/techarticles/BMW-X5/1...

This was all very strange !

Jumped the pins and nothing, so had another go after moving the plug (180deg ish) and the temp gauge went mad, full over then back to zero and back up again to max. This was dependent on ignition on full or engine running.

After this, plugging the sensor back in, fired up but then immediately stalled and wouldn't start without a bit of coaxing (throttle) so i suspect it has nudged the ECU in some way (Pete, 4 wires in the plug not 2?? Penelope, ECU )

So i have a feeling its cable/plug connection based hopefully before they disappear into the main loom, that's only a few inches..


Might not know much more for a few weeks so will revisit when the easterlies arrive


On the upside i drove out for 10 Mins just to get up to normal temps ...



ste phone pics but a small thank you

[InYaMooey]

Small update:

Pulled the cluster (Ms Stopit) re seated the connectors, also untwisted the loom a little.

So far fault not happened today (10c ambient and this when it normally starts playing up)

So will see how it goes

Only downside is I’ve lost my hard earned 25mpg average

[InYaMooey]

Penelope Stopit said:

Good of you to update, fingers crossed

No need for "Ms", she's a he

Prefer Ms anyway

Update 2: I spoke to bloody soon !

Just went out again as now 8c and dial went up to max again

Just once on the drive a tap on the top of the dash sorted it but this only helped once !!! (It’s also still intermittent so could be a coincidence I suppose..)

Pulled dash pod and fiddled with wires/plug and nothing helped.

I’m thinking deeper in the pod/circuit board dry joint

I’m wondering if a little electrical contact cleaner on the plug or socket might help or possibly a tiny bit of WD40 ?

I’m reluctant to break the pod apart but might come to that ..

[InYaMooey]

Thanks for that, I have been in there previously and re seated the plugs before (can’t remember why) but will check again.

It behaved today (but only 11c) this was after I pulled the pod late y’day and had another fiddle (read tapped the back of the pod on the temp gauge side)

Fingers crossed again

[InYaMooey]

Problem solved mods please can you mark the title as solved ?

Just to update and thank all for ideas contributions.

It turned out to be the Thermostat !!

I pulled it for inspection and saw it was not closing 100% (1-2 open) so thought possibly the main ECU was detecting a slow warm up and defaulting to max but couldn’t work out why on some journeys the gauge would revert to normal position.

Had ordered a new 95 deg stat (long story) but this didn’t have the extra connector so didn’t fit it.

As my original stat was out I broke it down and refitted without the internals so I could use the car to pick the new original 105 deg stat.

The gauge started behaving !! So now thinking not a slow warm up fault..

Anyway now all sorted and has been perfect the last few days

The stat appears to have an internal electrical contact which was very dirty or possibly not making a good contact due to being slightly open.

I also broke the socket off to see inside and looks pretty bad.

Non the wiser what was actually causing the fault but now thankfully sorted out.

Will attach some pics for reference

Thanks again all









And the new one





Still can’t work out why it was ambient <10c related

Edited by InYaMooey on Thursday 18th March 19:54