Hello all. I'm a former D3 owner and now owner of a 2009 3.6 TDV8. Very pleased with it so far bar a few bits of tidying needed here and there.

I've noticed that the temperature gauge (coolant temperature) seems to climb to normal and then - occasionally - will drop back down to cold. At least I'm pretty sure my eyes aren't deceiving me. I noticed also that the HVAC system dropped out when this happened (presumably because it thought it would only be blowing cold air into the car rather than warming it).

Can anyone offer any pointers? I presume the prime candidate would be the coolant sensor / plug / wiring...

Worth noting that a faulty oil temperature sensor can cause the coolant temperature gauge to go abit mad.

Interesting thanks. So is checking live values my best first step in that case?

Yeah I would give the live sensor values a check if you have access to a tool that will let you do that.

Only found out about the oil temperature sensor issue, as a mate was chasing odd temperature gauge behaviour and one of the better techs when told what was happening went straight to the issue.

Did an oil change last week and intended to change the oil temperature sensor but discovered that it needs a 30mm deep socket. Closest I had was 32mm. So completed the (very messy) oil change and ordered a new socket.

Got around to fitting it yesterday and there was a bit more than a trickle of oil came out. More like a geyser. Managed to stem the flow with the new sensor and got it torqued up.

Time will tell but I'm optimistic this will cure the issue as the live values for the oil temperature were up and down like a yo-yo corresponding closely to the antics of the temperature guage. 2016 Skoda Octavia VRS Estate
<gone>2009 FF Vogue TDV8 Buckingham Blue</gone>
<gone>2015 BMW 520D SE (not my favourite car)</gone>
<gone>2009 D3 HSE Galway Green</gone>

Fingers crossed it sorts the issue out.

My gauge did exactly that! Then I had a new oil sensor temp sensor fitted! Gauge now works as it should  2014 vogue se

Good news - it seems to have cured it. Thanks for all the help. 2016 Skoda Octavia VRS Estate
<gone>2009 FF Vogue TDV8 Buckingham Blue</gone>
<gone>2015 BMW 520D SE (not my favourite car)</gone>
<gone>2009 D3 HSE Galway Green</gone>