Coolant temp at a steady 79 degrees

[sulaiman]

Hi guys,

Can anyone offer some advice as to why my coolant sits at a steady 79 degrees once warmed up? It will occasionally rise to 80 and will then start showing 90 on the instrument panel but most of the time the CTS reads 79 degrees on block 49 of the climate panel and sits just below 90 on the instrument panel.

It's worth mentioning I have a new Coolant temp sensor fitted within the last year and no fault codes on VAG COM.

Cheers

 

[StupidFlanders]

sound like the thermotstat . Mine did the something similar , as the temp gauge is not that acurate . after changeing thermostat My vag com says temp is 97 but gauge is bang on 90 . Before gauge read 80 but temp was 61 on vag com. What engine code do you have ? as my temp on agu is block 3 or 4 .

 

[<tuffty/>]

If the dash is reading 90 but VCDS is showing 79 in the engine module then your CTS is the problem.. the CTS contains two temp sensors... one for the ECU and one for the dash... they should always read more or less the same but if they don't then is most likely the CTS at fault...

I think the dash temp can be seem through the Instruments module (17) but not sure what block so cycle through them until you spot the temp...

Compare this to the engine temp when the dash is reading 90 deg and see if there is a difference... should be no more than a degree or so... if the dash is reading 90ish and the engine 80ish then I would say replace the CTS...

<tuffty/>

 

[sulaiman]

Hi guys, thanks for the responses.

Dash temp is block 49 on the climate panel and that was the one reading 79degrees, while the clocks showed just below 90 (approx 88).

Only when the dash temp reaches 80degrees on occasion is when my clocks show 90degrees bang on. I know it is normal for the clocks to show 90degrees when the engine temp is between 80-110, but my problem is the dash temp reads 79 most of the time hence just putting it out of the 80-110 range and thus shows approx 88 on the clocks.

However I didn't realise block 49 was dash temp, so the next time the car is warm I will compare engine temp and dash temp with vag com and report back.

Tufty do you still think it is the CTS? I know this sensor works 100% as I fitted a genuine Audi part last year and had it in my old car without any problems and have only just swapped it over to my new one because the previous sensor had a open or short to ground intermittent hence me changing to the one from my old car.

 

[aragorn]

49c on the climate is replicating the instruments temperature, not the ECU temp.

The guage lies, as its designed to point at 90 across what audi consider the normal engine operating range, ie 80-100c.

As a result the gauge isnt linear thru its sweep.

I had a similar problem (though it only manifested at high speed ie motorway driving) where the gauge would drop to 80-85c. A look on 49c showed that the coolant temp was wandering around anything between 70 and 80c, at 80 the gauge would sit JUST below 90, and at 70 the guage would drop to about 80.

I was certain it was the thermostat, as at lower speeds the temp would rise, but i had a weird warm starting issue so i chagned the CTS, and it was exactly the same. Swapped the stat out at the weekend and now 49c sits at 92 and the guage never moves from 90.

One way to be sure its the stat, is get the enigne up to temp (ie drive it around for 10mins) then park up with the engine running, ensure the electric cooling fans are not running (ie AC off) and watch channel 49c. After a few minutes the temp should start rising, and it should climb past 90 before the cooling fans cut in automatically around 95-100c. If that happens its almost certainly the stat. If it just sits at 79 after 10-15mins, then its quite likely its the CTS.

 

[sulaiman]

Thanks for the help,

I checked the difference in temp on vag com between the engine and instrument modules and the reading is near enough the same 100% of the time, so I know the CTS is working.

After letting the car idle after a journey the temp rose very slowly but eventually reached 81/82c and the clocks started showing 90c. I will change the thermostat and let you know how I got on.

 

[Kave]

This is exactly what happened to my pd130 tdi, thermostat was sticky.

 

[stevie e]

Thermostat