Hello, recently i noticed that my Octavia 2.0 tdi 103 kw would idle at 1000 rpm till the temperautre hits 90°c (usually was till 70°) so i checked temps with diagnostics, diag says 75° but on dashboard its 90°. I replaced two sensors that i could find, one on the drivers side and one on passanger side. I was wondering are there any more sensors or is the problem something else. Thanks in advance.

Are you speaking of coolant temperature sensors or the dashboard heating duct sensors?

@J.R. coolant temperature, but what i'm saying is that on instrument cluster it shows 90°c coolant temperature.

1. The idle speed of 1000 rpm is normal if the battery is being recharged - especially if you are also feeding heavy loads such as a window heater(s) and lights. It will return to the normal 700 rpm when the battery reaches normal float voltage. Not related to coolant temperature.

2. The "clever" software that drives the coolant temperature guage reads 90C over a wide acceptable coolant temperature range both cooler and hotter than actual temperature.

On both points what you described is normal and you don't have a problem.

 

Points 1 and 2 have been a feature of VAG cars for over 20 years but it still catches out newcomers.

 

Were the two temperature sensors you changed in the cabin? If so they are associated with Climatronic cabin heating.

4 hours ago, pikpilot said:

1. The idle speed of 1000 rpm is normal if the battery is being recharged - especially if you are also feeding heavy loads such as a window heater(s) and lights. It will return to the normal 700 rpm when the battery reaches normal float voltage. Not related to coolant temperature.

2. The "clever" software that drives the coolant temperature guage reads 90C over a wide acceptable coolant temperature range both cooler and hotter than actual temperature.

On both points what you described is normal and you don't have a problem.

 

Points 1 and 2 have been a feature of VAG cars for over 20 years but it still catches out newcomers.

 

Were the two temperature sensors you changed in the cabin? If so they are associated with Climatronic cabin heating.

Thanks for the reply, but i'm not a newcomer, i've had the car for 4 years, yes all of that you said is true, but voltages are fine, battery is new, and high idles newer in these 4 years occured above 70°c, there are no fault codes on diagnostic, only thing i've found is that coolant temp is not reading correctly. Sensors are both in the coolant hoses, inside temp was reading correctly so i didn't bother with those sensors, but if you have any other pointers i would be thankful.

Is it a DSG gearbox?

The reason I ask is that there is a coolant thermostat for the gearbox in DSG equipped cars which is almost always found to be the cause of lower than ideal engine coolant temperature when it fails.

 

Lots of threads about it in lots of the subforums.

9 hours ago, Breezy_Pete said:

The reason I ask is that there is a coolant thermostat for the gearbox in DSG equipped cars which is almost always found to be the cause of lower than ideal engine coolant temperature when it fails.

 

Lots of threads about it in lots of the subforums.

Yes it is, thanks i will look for it.