Erratic temp gauge

[Rtaylor2208]

So for a long time now I have been putting up with a rather erratic temp gauge. Basically it stays steady rising to operating temperature between the half and 3/4 mark.

It's fine for about 10 mins then starts bouncing all over the place, if I stop the gauge immediately settles back to around half way. It's worse at motorway speeds than around town.

I removed the cluster and tightened the brass nut on the back and that has made no difference.

There is no signs of a failed head gasket I.e no mayo in the oil, no oil residue in the coolant, no loss of coolant and no white smoke.

I'm not 100% sure the viscous is OK though as I tried the test of the old rolled up newspaper and it did stop the fan but not immediately.

So all I can think of is possibly a failing water pump making the temperature erratic or the brown sensor is playing up.

[Rtaylor2208]

I should also mention that the timing belt, tensioner and all v belts were replaced less than 200 miles ago, but I did not replace the water pump as it looked fairly recent.

[bimanut]

might be a daft thing to say but you say you tightened the brass nut and not plural there are two brass nuts.Had the same problem one of my mine was missing

[Rtaylor2208]

On the back of the cluster there was only one nut directly behind the guage on the outer casing of the cluster.

[Brianmoooore]

Pull the plug off of the brown sensor, and connect a 330 or 470 ohm resistor between the single pin in the plug and a good earth. This should make the gauge read somewhere in the middle section when the ignition is turned on.
If the reading is stable, then the brown sensor is probably faulty. If it's still jumping, then further investigation is needed.

[Rtaylor2208]

Thanks Brian looks like its off to the electrical store tomorrow to source one, I'll post back once I know more.

[harry_p]

I've had a broken wire under the rubber boot just behind the plastic connector on the temperature sensor cause the exact same symptoms.

[Rtaylor2208]

Thanks harry_p that's something for me to look for tomorrow as well.