Hi, my temp gauge has been acting up

for a while...under normal stop start driving at this time of year it sits about 70 degrees (see pic) On the motorway it can sit flat at the bottom of the gauge depending on the outside temp and if I’m running the heater. During the summer it will sit at 90 degrees and drop down to 75/80 on the motorway. Oil temperature goes up and down too. I feel as if performance is being affected when it gets too warm although that may be paranoia on my part. 
 

I’ve suspected a faulty coolant temp sensor so ordered one from eBay and fitted it but it hasn’t solved a thing. Now I’m thinking thermostat. So before I get the mechanic to strip half the car and charge me huge labour part to fit a £12 ‘stat does anyone have any other ideas as to what’s causing this? Do I need an OEM sensor for example?

 

This has been annoying me a while now so the car is not overheating and DPF regens are fine. 
 

Many thanks. 

Sounds most like a stuck open thermostat to me?

Or DSG thermostat if you have that type of gearbox?

Seems more common failure than engine thermostat. Easier to change too, I believe.

25 minutes ago, PetrolDave said:

Sounds most like a stuck open thermostat to me?

It must be the reason. Just watched a German bloke change one on an Audi with the 2.0 litre tdi. Doesn’t look as daunting as I first feared. I’ll try and persuade the mechanic to have a go. I always assumed a stuck thermostat would either stay shut or stay open but perhaps this one isn’t fully opening or closing. 

How is the heater output?  How long before you get any heat coming through?

13 hours ago, ords said:

How is the heater output?  How long before you get any heat coming through?

Quite quickly tbh. That’s the strange thing, heating seems normal.  I’ll get the thermostat changed but if nothing changes then I’m stumped. 

I presume you ignored my post because you don't have DSG gearbox?

When replacing a sensor that involves so much labour, I would be tempted to fit the very best available to reduce the likelihood of having to replace again. That cheapo part of ebay could be a false economy.

 

182000 miles in a 2015 car! Taxi?

21 hours ago, Westbury63 said:

When replacing a sensor that involves so much labour, I would be tempted to fit the very best available to reduce the likelihood of having to replace again. That cheapo part of ebay could be a false economy.

 

182000 miles in a 2015 car! Taxi?

Yes, she has been very reliable. I think she’s cost me (including consumables, tyres, services and MOTs) about £1500 to run in those years. 
 

The sensor was OEM but I might just purchase a VAG one. 

On 28/01/2021 at 08:09, Wino said:

I presume you ignored my post because you don't have DSG gearbox?

Sorry, yes. 5 speed manual.  

Did you not know that almost all the Taxis in Glasgow are Octavias?? :-)

8 hours ago, gm73 said:

Yes, she has been very reliable. I think she’s cost me (including consumables, tyres, services and MOTs) about £1500 to run in those years. 

 

That's great service and low costs. Good to hear about reliable cars!

 

4 hours ago, varaderoguy said:

Did you not know that almost all the Taxis in Glasgow are Octavias?? :-)

 

They are in most places !!

Another thread.

 

22 hours ago, varaderoguy said:

Did you not know that almost all the Taxis in Glasgow are Octavias?? :-)

Any driver I know who changed to a Ford or Citroen had always went back to an Octavia. The problem being the Mondeo had the PSA Diesel engine and the same issues as any Citroen or Peugeot. I had a Berlingo for a year and I hated it, it was finished as a taxi at 140k. Couldn’t wait to go back to an Octavia and now I’m on 183k pretty much trouble free miles (touch wood). 
 

Many also changed to Hyundai i40s back around 2013. You don’t see any of them at all anymore despite the 7 year warranty.