New thermostat temp still not hitting 90

[jackal_s3]

Just had the thermostat replaced in my S3 but the temp still doesn’t hit 90. It gets much closer to 90 than it did before but sits just under it and doesn’t fluctuate as much as before, still fluctuates maybe a needles width.
It’s going back to the garage that changed it this week but any ideas what this could be?
Cheers

 

[s5joe]

Temp sender unit it is on the pipe that goes to the thermostat

 

[jackal_s3]

Is that the coolant temp sensor? The nice cheap little part? Had to change one on my 1.8T few years back.
Would the dodgy thermostat/temp sensor affect MPG as I know the S3 ain’t built for economy but currently my MPG is looking pretty poor even by S3 standards.

 

[LEE69]

Yes it will affect it, have you got something to read the coolant temp ie vcds or and obd reader?

 

[jackal_s3]

Just a cheapo OBD code reader, garage said it was the thermostat and it had made a slight improvement to the temp gauge but still not right.
Is it common for both to go at the same time or have I been conned into the more expensive repair?

 

[Nessy]

In all fairness to the garage it is often difficult to diagnose which is dodgy when you get erratic temperature gauge readings , is it the sensor or the thermostat that is the cause?
I had a B5 A4 for almost 11 years and the lifespan of the OEM coolant temp sensor seemed to be about 5 years as I did the job twice during my ownership and it had already been done when I bought it at 6 years old.
Shortly after acquiring my current A3 I had erratic temp gauge readings so replaced the thermostat but this didn’t cure the fault, however a new coolant temp sensor did.
One question, did the garage fit a Genuine thermostat?
Apparently non-Genuine stats have a very bad reputation for reliability out of the box which is why I only ever fit Genuine thermostats and coolant temp sensors.

 

[s5joe]

Yes the sender unit does affect the mpg on these as it tells the ecu how hot the car is to fuel it etc.

 

[jackal_s3]

Cheers for the reply folk, sounds like it could well be the sensor then. I’ll get it changed when it goes back in

 

[Shiz94]

Cheers for the reply folk, sounds like it could well be the sensor then. I’ll get it changed when it goes back in

Let us know how you get on

 

[jackal_s3]

Update - had the CTS changed but also got the timing belt and water pump done as had no record of it being carried out by previous owner and old water pump was found to be leaking slightly so this could also be the cause of it.....either way car gets to temp now quickly and holds!