Water temperature dial working sporadically

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Ingwe

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Hello,
During a long drive yesterday (450 miles) I noticed that the water temp gauge, normally showing 90°, was not registering. There were no performance issues and the oil temperature didn't rise above normal. Then after a few minutes, I noticed the water gauge was back to showing 90°. Then this morning, when I started up, the water gauge didn't move showing 0.
Is this likely to be a faulty gauge i.e. sender, airlock in the coolant, loose wire or something else. As I say, performance didn't seem affected.
It is a 1998 A4 with 162,000 miles.
Many thanks.
 
The usual issue is a bad thermostat. On a motorway run the coolant simply doesnt get hot enough, and the guage never moves. When you slow down in town or get stuck in traffic you'll see the temperature rise up as theres less airflow.
Less common is a bad sensor.
If you have climate control you can view live coolant temp on the climate unit by pressing recirc and up together, using temp +/- contorl to make the display read 49c, then press recirc again.
 
This is helpful, thank you. But what happened was the temp gauge showed 90 on the guard for most of the journey. Suddenly it went to 0. Then after half an hour or so, it went back to 90.
So it isn't a question of the gauge not working at all, but it appears some intermittent problem.
I'll try and use the climate control as you suggest to see the coolant temperature.
 
A correction to my earlier post. When the gauge goes back it is to 60. There is no "0". 60 was the normal position.
 
Did you do anything about it? I'm minded to ignore it as the oil temperature doesn't increase and there is no performance drop off. Funnily enough, it worked for 345 miles, then flipped to 60. Then the next morning, drove to the shops as normal and it gradually rose to the 90° position as per normal and worked the rest of the day.
 
Sounds like a stat TBH.

As an aside what engine variant is it?
I ask because ...I had an issue with a long term coolant leak and it turned out it was a coolant sensor housing moulding line opening at high temperature.
I fixed this by replacing it with the alloy version from ECS tuning...

I say this because the water temp sensor housing goes brittle with age and you MAY end up changing this as well if you are unlucky enough to damage it whilst working on car.

The engine variant comes into play as on the AJL it's quite straightforwards unlike other variants that have an element of "risk" of damaging the block if you cross thread any of the support brackets for the xtra gubbins that some variants have tucked away in the way...

PS don't ask me about the oil leak that turned out [eventually after changing quite a few bits and bobs] to be a weep up through the internals of the oil pressure switch and out via the wire holes!!!!
 
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