V6 petrol additional temperature gauge issues

[Mark-H]

Hi All,

Bit of a weird one, hopefully someone can point me in the right direction.

Last year I did the temp gauge mod where you loop out the diode and add a resistor to remove the dead-zone and have a more useful gauge. All was fine.

Although the van has been working absolutely fine and the gauge was doing what it should, the needle was a bit too far to the right when operating at "normal" temperatures. I experimented with resistor values and could influence where the needle went but thought I'd replace the resistor with a variable resistor so I could tune it to be at 12:00 fit normal. Should have left well alone!!!

Took off the 150ohm resistor, extended the wires, added a 0-200ohm linea pot, set it to 150ohm and connecte4d everything back up. Temp needle goes hard right on a "room temperature" engine. Adjust and no change. Go open circuit and needle drops to left. Put the 150ohm back in and still hard right. Check I've not shorted something with the screws on the back of the temp gauge and all looks OK. Put it back as-was and still does the same. Removed the original mod (took link off the zenna and removed resistor) and still does the same.

If you pull the wire off the sender (single wire connector front of engine) the gauge drops but as soon as you reconnect it then it goes hard right.

Anyone had anything similar before?

I'll fir a third party temp gauge for now but keen to get the stock one working.

Any tips on where to fit the sender for a thirdparty gauge?

[g8dhe]

The actual circuit is;

TempGaugeOriginalCircuit.JPG (18.16 KiB) Viewed 3024 times

The additional resistor is added across the temperature sensor itself apparently according to the original write-up.
If its going full scale then it sounds like the sensor is being short circuited somewhere?
The sensor is a 3119 device https://www.mte-thomson.com.br/wp-conte ... a-2018.pdf some details in this catalogue including NTC parameters.

[Mark-H]

Thanks Geoff. Unfortunately the datasheet does not tell you the expected resistance at any given temp. Not in the manuals either. No idea at the moment whether the sender, cluster, gauge or wiring are at fault. Will let it get frozen tonight and see if it manages to drain a CR network somewhere and kick it back into life. Really annoying when something was 80% good is not 100% useless

Don't really want to have to drain the coolant to try a new sender "just in case" but suspect that may be next move.

[g8dhe]

Er Page 34 ?

[Mark-H]

Cheers. Will let it get really cold tonight and see what it does in the morning. It all seems like passive components so can't see that anything needs to learn parameters etc but maybe (hopefully) the sender hasn't really had to work for the last 3 months and got upset when it got properly hot for the first time. Will see what the morning brings. Any idea if you can change the sender without draining the coolant? It the system watertight enough to not flow out? If not, guess it gives me a chance to practice the bleeding system once again. If I drain it through the sender hole then shouldn't be too much drama.

[g8dhe]

The sensor is high up but can be difficult to reach;

One is the two-wire feeding the ECU and the gauge is the single Green wire.