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[Clarkey]

Hey all, not been on here in some time.

I have recently put my Omega back on the road after being parked up a number of years. It is a 2001 3.2 Auto. I just fitted a new thermostat but still have no engine temp reading on dash. I plugged in tech 2 to check live data and did an actuator test while I was at it. Engine at operating temp reading 90deg C in engine ECU live feed. When I check engine temp from instrument feed it reads 60deg C at operating temp. I know there are 2 sensors on coolant bridge at back of engine. I took wire off single contact sensor as I thought this was for instrument temp feed and put it direct to earth which turned on engine overheat light but did not move temp gauge. I also tried a replacement dash and got same result. Does single wire sensor simply operate overheat light or does it supply engine temp signal to dash as well?

Thanks in advance,

James.

[Doctor Gollum]

That is the dash temp sensor. The fact it grounds the light on suggests the wiring is sound... Doing this should also move the gauge. Did you try with the ignition on? If it still doesn't move, then a new sensor is probably on the cards with the following caveat...

Could also be that the gauge itself is stuck... A gentle tap of a couple of potholes may be enough encouragement.

[Clarkey]

That is the dash temp sensor. The fact it grounds the light on suggests the wiring is sound... Doing this should also move the gauge. Did you try with the ignition on? If it still doesn't move, then a new sensor is probably on the cards with the following caveat...

Ignition was on when I grounded wire. Was surprised gauge did not move yet overheat light on when I grounded wire. When I performed actuator test with Tech 2, needle went to max and light came on. As engine temp showed 60deg on instrument data feed it was not registering hot enough to move needle.

Could also be that the gauge itself is stuck... A gentle tap of a couple of potholes may be enough encouragement.

I've tried a couple of "gentle" taps when driving at the beginning. Looks like replacement sensor is the way forward. Before I fit it can anyone tell me the correct code index for the instrument panel for my machine?

Thanks for reply Doctor G

[Doctor Gollum]

If you have access to the live data, is the ECU seeing the coolant temp

[TheBoy]

ECU and dash sensors are separate on the 6 cylinder ones (not sure about 4, as never owned one).

Ground the single wire for longer - the dash gauge is massively damped (30+ seconds) - to see if it moves needle.  If it does, replace the sensor (or check it for a large build up of crud, which if it has, this will likely also be present throughout the coolant system, so you know what you need to do!)

[Doctor Gollum]

ECU and dash sensors are separate on the 6 cylinder ones (not sure about 4, as never owned one).

Ground the single wire for longer - the dash gauge is massively damped (30+ seconds) - to see if it moves needle.  If it does, replace the sensor (or check it for a large build up of crud, which if it has, this will likely also be present throughout the coolant system, so you know what you need to do!)

4 pots have the same set up although the coolant 'bridge' connects one side of the head.to.the other rather than joining two heads

[Clarkey]

ECU and dash sensors are separate on the 6 cylinder ones (not sure about 4, as never owned one).

Ground the single wire for longer - the dash gauge is massively damped (30+ seconds) - to see if it moves needle.  If it does, replace the sensor (or check it for a large build up of crud, which if it has, this will likely also be present throughout the coolant system, so you know what you need to do!)

Thanks TheBoy. You are the man. I was over thinking this. New sensor ordered.

[Clarkey]

Update on this. I replaced engine temp sensors on coolant bridge (did both while I was at it) and still have same issue. At operating temp (engine ecu live data 95 deg) the live data in instrument reads 65 deg for coolant temp. Same thing with spare dash I acquired. I then let the engine cool and rechecked. Engine temp was 25deg in engine ecu feed but reads steady 50deg in instrument live data. When I ground single wire for temp gauge, overheat light on but temp reading on instrument live data is 0 deg. What am I missing?

On another note the rev counter was reading too high. I had to reprogram code index on instrument from 12 to 7 to have it register correctly. I have no idea how code index changed but wonder if some time in oven after respray could have caused issues. Am open to suggestions.

J.

[Clarkey]

Another update on this. At operating temp the dash was still reading 60deg C. I decided to freshen up all earths engine to body and body to battery. Main earth point under battery was cruddy & benefited from a clean some copper grease. This did not resolve issue but when I ran an earth from the battery and touched the coolant bridge at back of engine when running at operating temp, the gauge went immediately from 60 deg to 91 deg. When I removed earth temp reading dropped again. When I ran earth from bolt on head to coolant bridge the reading was correct. It would seem the coolant bridge is not earthing correctly to engine, thus giving too low temp reading. Am gonna strip intake off in next few days and install a permanent earth.

[TheBoy]

If you're putty grease on the coolant bridge bolts that go through the dougty washers, you will be insulating to an extent.  I believe this is where the coolant bridge would get its 0V.

[Clarkey]

If you're putty grease on the coolant bridge bolts that go through the dougty washers, you will be insulating to an extent.  I believe this is where the coolant bridge would get its 0V.

My thoughts are to run an earth wire from under engine temp sensor to head. Just need to get eye connection correct size.

[Doctor Gollum]

Electrical contacts need to be clean metal to clean metal in order to be effective. Start there.

Electrical contacts cleaner and a wire brush. Dry and connect. If you then want to coat them to prevent corrosion, that's fine, but only AFTER making the connection.

[Clarkey]

Electrical contacts need to be clean metal to clean metal in order to be effective. Start there.

Electrical contacts cleaner and a wire brush. Dry and connect. If you then want to coat them to prevent corrosion, that's fine, but only AFTER making the connection.

Good points and well made. Took your advice and I now have a working engine temp gauge again.
Bridge looked like this before removal.



Banjo bolts and douty washers were in a poor state.



Cleaned up bolts and new washers. Sanded surfaces making contact.





End result.

[JamesV6CDX]

Absolutely bloody brilliant, well done on a great fix

[Dave G]

Wish I'd seen this thread earlier (no pun intended) - I might have been able to contribute something useful for once!
I'd struggled to find dowty washers when doing head work - but I thought I'd done a pretty good job of 'refurbishing' the old ones...


And I had - absolutely watertight - but also superbly electrically insulating! I'd wrapped a spiral of ptfe tape around them, a thin film of RTV then a thin fibre washer under the bolt so as not to chew up the tape.

Ooops - no temp display. Help from OOF was forthcoming - so I put a short wire from under the sensor to a nearby bolt to reinstate the ground connection.
Done.