Changed coolant temp sensor now problems :(

[J Eyo]

So had a hard starting issue changed out the coolant temp sensor. Never had any problems besides the hard star and it always sat on 90. Since changing, the hard start problems have gone but the needle very rarely leaves 60 and will sometimes hit 90 if I just let it idle. Help!! Air bubble? Can't be a bad thermo as everything was fine before I did the swap, also switching back to original thermo brings back a hard start but the temp still sits on 60. Also it's made the idle after driving for about 30 rough, like it's misfiring? What's happening here??

 

[Greg-S3]

I'd be tempted to try another switch, where did the switch come from? It could be a faulty thermostat also.

 

[J Eyo]

Thing is I put the original sensor that was working fine and it still sits on 60 when before it sat at 90!

 

[Tooks]

So, if I understand correctly, you've just changed the temp sensor, which has fixed your hard starting issue?

But now, the temp never gets over 60?

It could be that the water temp sensor was masking a dodgy thermostat, and now you've fixed the temp sensor and are getting accurate temp readings, the stat issue is visible.

I'd change he thermostat, it's a fiddly job, but the part isn't expensive and you don't need to lose all the coolant if you're quick swapping it out. In my experience, the A3/S3 is pretty good at bleeding itself, so unlikely to be an air lock.

Not sure why putting the old temp sensor back on still gives a 60 reading, but it could be the old 'more than one problem at once' issue or just plain bad luck that the stat has gone too...

 

[Greg-S3]

Have you damaged the multi plug? Get a thermostat in it before anything else