Coolant temp

[Muskokaman]

My Octavia 1.9tdi has reached 200,000 miles with very few problems but one ongoing mystery is why the coolant temp on the dash shows it at mid point (normal) for most of the time but occasionally drops back a bit. I'm no expert but I can't see how the engine gets cooler for a bit then heats up again! The coolant sensor has been changed but it still happens. Could it be the thermostat?

[Glynn]

My 2.0tfsi has been doing this for about a year and i just cant figure it out!

[booke23]

My Octavia 1.9tdi has reached 200,000 miles with very few problems but one ongoing mystery is why the coolant temp on the dash shows it at mid point (normal) for most of the time but occasionally drops back a bit. I'm no expert but I can't see how the engine gets cooler for a bit then heats up again! The coolant sensor has been changed but it still happens. Could it be the thermostat?

 

Yes, I think the thermostat would be the next thing to replace. They sometimes go a bit out of spec with age and behave like this, however I have also heard that the thermostat housing can warp with age and produce similar symptoms.   

[Guest]

Apparently the efficiency of the engine is such that there is less waste heat being generated.

Therefore if the engine is not being worked and the heater is on there will be more demand than supply, resulting in the engine cooling down from normal operating temperature.

I've never seen the temp gauge go above 90deg C on my 1.9PD 105 and if left to idle the temperature does drop to 70degrees or thereabouts.

No chance of the cooling fans activating while idling, like on most cars I've experienced.

[willy0329]

Yes you need a new thermostate,running the car with a faulty thermostate will effect the performance and economy of the engine as the car thinks its running under normal working temperature,  I got one for my tfsi in gsf it was under £30 the main dealer quoted £35 then when the part arrived they wanted £70, it was a pig on the tfsi to fit its hidden at the front of the engine not sure where it is on the diesel .  

[Muskokaman]

Thanks folks, it was the thermostat. Picked one up from Motorcount for about £7 and fitting it to the tdi was dead easy. Interesting what you said micmac about the engine temp. I have been worrying about mine since I noticed the fans were never on when I looked. Got to leaping out when I got back from the shop and having a look. However I still worry a little that although changing the thermostat has stabilised the reading at 90, the hose from the thermostat housing is often still cool when I've done 10 to 20 miles, although it does warm up after a longer journey.