(T) Temperature Gauge issues

Ok, its been a while since i've attacked this - but i wonder if anyone know will be able to shed some light on this.

The temperature gauge in my cinq has never worked since ive had it. It just sits at the bottom, not moving. To attempt to fix this i have done the following:

Replaced the temperature sender in the head, its checked and gives a varying resistance to ground as the temperature varies. Conclusion, it works.

Replaced the temperature and fuel gauges themselves with a known working one.

Replaced the whole instrument cluster with a known working one.

Check the cable running from the gauge to the sender unit, and it was fine. Ran a seperate cable down there too and bypassed it just to be sure.

I cannot think of anything else that would effect it. Ive cleaned and sanded the earth connections under the bonnet - but not the dash earth. Tho i'm having no other electrical problems on the dash, so doubt its that.

I'm at a loss..still.. anyone any ideas?

Isn't the temp guage also connected to the ECU to give the ECU readings for fuelling?

Could possibly be something amiss here.

Liam

Have you got power to the gauge? Check the plastic backing with all the tracks on isn't cracked or split anywhere.

Arc .... you said you checked the wiring from the cluster to the temp sender can I ask how you did this? It could well run through the ECU unfortunally I dont have a diagram to hand.Just incase dont use a ohmmeter or you'll blow the ECU if it does indeed run through this.

Hi,
There's two temp senders on a cinq, one for the ecu located on the thermostat housing on the 899cc not sure about sporting and one for the dash gauge located on the cylinder head.
Have you fitted the correct temp sender for the gauge, as far as I know there are two types for the dash, one for a gauge and one for a light, cos not all models have a gauge......

Thanks
Paul T

the sender i have is a for a gauge, not a light. If it was for a light it'd be a switch, and the resistance wouldnt change with temperature. All 1108cc cinqs had gauges.

The sender for the gauge doesnt go near the ECU, and i was able to test it by looking at the wiring diagrams at the back of the haynes manual and tracing the wire into the dash. It is a peice of wire, no funny buisness going on on it.

Pete - ive replaced that plastic back bit in a desperate bid to rule out any problems with it.

When i touch the wire running to the gauge onto the block, the gauge shoots to the top. That says to me all the wiring, and the gauge itself is working and that the sender is at fault. Origonally i thought that was the only thing wrong with it, hence i replaced the sender unit first.

I have a temperature gauge to go in my spare A pillar pod, but it annoys me to see a gauge on the dash dead.

Hi,
When you replaced the sender did you use ptfe tape for the seal, it can stop the sender from earthing out, try puting a jump lead from the casing of the sender to the engine lifting eye to make sure you have a good earth for the sender.....running out of things to suggest otherwise.....

Thanks
Paul T

already checked that.. i thought the same at first. I used PTFE tape But the casing is grounded, and the inner bit gives a varying resistance to ground at different temperatures.

Its had me totally flumoxed since i bought the car.

Hi,
Can you measure the resistance at the dash multi plug end, compared to right at the sender, there could be an extra resistance in the wire/connector somewhere.........

Thanks
Paul T

I thought we had concluded this a gypsy curse?
Its basic electrics gone wonky. Everything works independantly but not together.

checked that, theres an extra 0.01 ohm or so.

im thinking gypsy curse.. yeah

Hi,
Thats not going to make much difference........gypsy curse it is then....

Thanks
Paul T

Have you a good engine earth? Any chance of scanning & posting up the wiring diagram? Gotta be a logical explanation for this

all the earths under the bonnet were cleaned and sanded when i did the HG - it made no difference. My haynes manual is back home, so can't post a diagram up. But there really is nothing complicating going on with the gauge. I know what i'm doing with electrics (did electronics at A-level), but can't see anything wrong with this at all.

I'm going to go have a play with the car now tho, see what i can turn up.

Can someone do me a favour? Check the resistance of their sender unit with the engine cold, and then with the engine at operating temperature? Cheers

OK you say you changed over the cluster,sender & checked relevant wiring.You say you earthed out the temp sender & gauge shot to full,have you fitted the correct sender? not unknown for parts to supply wrong part