2.5 V6 TDi Temp Sensor or Thermostat failure?

[Dr_Des]

Hi All,

Got my A6 (2001 C5 2.5 V6 TDi Avant) 2 days ago and driving it back to Austria from Munich it never really got up to temperature.

I've read LOTS of posts here and elsewhere about this issue but before I dive into replacing the thermostat I would be grateful if someone could confirm the correct diagnistic steps I should follow to confirm exactly which part(s) are failing?

The temperature only rose to just above 80deg when driving above 200km/h (gotta love the Autobahn!)

The oil temp guage is also showing very low temps although it does move slightly.

I do see some movement of the water temp gauge but certainly nothing like it getting to the 90deg I think it should be.

Thanks

Des

[NickPicks]

The temp gauge should sit exactly on 90 degrees.

I believe that the temp sensor has 2 sensors - one for the engine management, and one for the gauge. If you've got vagcom, you can read the engine management sensor temp in measuring blocks to compare.

Peter D on here usually recommends covering about 70% of the radiator with a sheet of cardboard. If it then gets up to temperature, then it's the thermostat that has failed. Unfortunately, it's virtually impossible to change the thermostat without removing the cambelt. (there's a couple of people who say it can be done, but most say it cannot)

[Dr_Des]

Hi Nick, Thanks for that, I will definately try the cardboard idea. As for the cambelt I would change it when doing the thermostat / water pump as it'd be madness not to ;-)

As for vagcom, I'm tempted to buy a licence from Ross-Tech.com and get the lead from eBay - Any thoughts on that as a plan?

Ta, Des

[Peter D]

Welcome Dr_Des
Best to quote your engine code, probably AFB in your footnote.
Will you be doing the job yourself. ?
Yes I suspect the stat. as it is cold and it is a TDI you may need to cover more then 70%
You can check the temp sensor with a meter. It should be 107 ohms at 90 degrees C.
What is the mileage and when was the cam belt changed last.
Regards Peter
Regards Peter

[Dr_Des]

Hi Peter,

Yep, sorry, the engine code is AKN.

I would expect to do the work myself, yes. Unless there are specialist tools that can't easiliy be bypassed.

As for the sensor, can you point me in the right direction to find it?

The car has done 190k KMS and I am told that the belt was last chenged at 120K

Thanks,

Des

[Peter D]

Under the engine cover left hand side as you look at it, mounted in rigid plastic pipe. 4 pin connector. Regards Peter

[NickPicks]

As for vagcom, I'm tempted to buy a licence from Ross-Tech.com and get the lead from eBay - Any thoughts on that as a plan?

A cheap lead from ebay should work with VCDS lite, but if you buy one for £20 from Gendan at this link, it's definitely compatible.

[Dr_Des]

You can check the temp sensor with a meter. It should be 107 ohms at 90 degrees C.

Can you tell me which pair of "pins" I should measure the resistance at? Also, do you know what the resistance should be at 20c?

Nick: Thanks for that, I'm on the case now!

Thanks

Des

[Peter D]

259 ohms at 60 degrees. I have not measured one cold i.e. 20.
There are two elements in the sensor and they should both measure the same.
Regards Peter

[Dr_Des]

Just a quick update - I have sent the instrument cluster off to be fixed as the pixcels were all mashed up so can't run the car at the moment.

I will try the cardboard test next week.

Thinking about the probablility of doing the thermostat replacement, are there any Audi specific tools that will be needed to make this job possible?

Thanks,

Des