Audi RS6 Coolant Temperature

[blues1955]

My RS6 2003 Saloon coolant temperature gauge is not reading correctly. When the ignition is turned on the needle moves very slightly to the right. As the engine warms up the needle doesn't move, staying totally on the left. I consider myself capable to sort out sensor or wiring issues but I have not started any troubkle shooting.

Has anyone experienced the same problem and can give some guidance? Thanks

[Magnet]

Hello Michael,

Many thanks for joining and posting your plea. 
Are you confident that the car is actually getting up to its proper operating temperature, even though the gauge isn’t indicating it is? 
If so, I would suspect the coolant temperature sender linked to the gauge, the resistance of which should change as the temperature increases. 
Try to obtain a reasonable quality one such as Bosch, although I have used Febi to good avail. 
Kind regards,

Gareth, 

[blues1955]

Hello, Gareth!

Thanks for your response. The car was driven 4 miles on a mixture of town roads and a by-pass and then sat idling for an additional 15 minutes. The engine bay was warm but the needle of the gauge didn't move, so I suspect a problem.

I assume that what you call the coolant temperature sender is the same as what I am calling the coolant temperature sensor. I have viewed some Youtube videos but haven't yet found one showing the location of the RS6 sensor. Can you please indicate where it is located?

I have one further question. I am not fully convinced that the oil temperature gauge is working. What should this temperature be expected to read after 4 miles of "light right foot driving" and 15 minutes idling? Where is this sensor located?

Regards,

Michael

[Magnet]

Hello again Michael,

I’ve always called them senders since their primary (and indeed only) function is to control the gauge. 
Others may call them ‘coolant temperature sensors’, but I reserve that description for such sensors that signal the correct fuel mixture etc. Gauge senders often have just 2 wire connectors, whereas the sensors have more - all a rule of thumb though! 
Oil temperature:- Some people assume that a car is up to operating temperature once the coolant temperature has reached normal i.e. with 2 to 3 miles. Not so, by that time, the oil is barely warm, and you need about a 10 mile run for the oil to be up to its optimum temperature. Definitely forget about idling! This will obviously be affected by outside temperature, but I would think about 110 in this sort of weather. 
Perhaps interesting that you suspect your oil temp. gauge maybe reading low as well, and there might (just might) be a connection between this and a low reading coolant temp gauge. However, your 19 year old car maybe too modern for this possible connection!  - older cars were fitted with a voltage stabiliser that dropped the gauge operating voltage to around 9 to 10v to damp the gauge from fluctuations. These units used to cause issues, but probably not on yours. 
Kind regards,

Gareth. 

[blues1955]

Thanks, Gareth.

I bought my RS6 on Friday and I paid attention to the water and oil temperature gauges on the test drive. It is possible that the car was not driven sufficiently far or "hard" enough to get the car up to normal operating conditions.  From my "normal" car experiences acquired over 50 years I would have expected the water temperature to have shown an increase on the gauge (but I could be wrong as I have no experience of a turbo super car).

I have an 23 year old MGF summer car which also has an oil temperature gauge and this will only "start to move to the right" after around 5 miles. The MGF runs with the temperature gauge midway but the oil temperature never goes above 80C (I assume this gauge is correctly calibrated). To be completely honest, I always keep an eye on the MGF's water temperature but only occasionally on the oil temperature.

It is possible there is no issue with the RS6 oil temperature gauge but I will buy 2 new senders for peace of mind.

I will keep the forum informed of how easy it is to locate these senders in the engine bay and replace them.

Regards,

Michael

[Magnet]

Hello Michael,

Many thanks for the additional information.

Private or trade purchase?

Test drives of say 5 miles should be sufficient for the coolant temperature to reach its normal operating temperature. If your test drive was shorter than that, or if it didn’t get up to temperature in that distance, then you are indeed in unknown territory. 
Has the car been transported to you then, since you don’t seem to mention anything of the ‘drive home’? 

Oil temperature -as already said - assess after a 10 mile run. It’s certainly not unheard of for new owners to find the oil light comes on part way home, when the oil gets up to temperature, so short test drives are always a chance. 
In your case Michael, it’s simply a case of test driving on that length of journey and reporting back with your findings. 

MGF?? Who have you upset then? - bless you. I guess someone has to own one! So that makes two of us now then, if you count in our TF! You should be well qualified to judge oil temperature gauges by now then. 
Just report back when you’ve done your test drive, but it would be interesting to have the rest of the background meanwhile. 
Kind regards,

Gareth. 

[blues1955]

Gareth,

Thanks for your replies to my RS6 temperature issue.

I will collect the car on Thursday this week. I have consulted a local VW/Audi specialist who recommends that I run a OBD check before changing any sensors. It sounds like good advice.

Regards,

Michael 

[Magnet]

Thanks Michael,

For ‘sensors’ , I’m still reading ‘sender’ for gauges. 
Of course, the drive home will confirm the true state of affairs. 
Perhaps you could let us know how you get on.
Kind regards,

Gareth. 
 

[blues1955]

Gareth,

I want to update you and any other members who have been following my problem. I picked up the car on Thursday. My fault reader device connected to the OBD gave me coolant temperature in real time (between 88 and 93 C). Interestingly the temperature gauge jumped into life during the journey, indicating 90 C. However the reading dropped totally to the left after a while and later again read correctly. The oil temperature gauge which reads between 60 and 180 C indicated a constant temperature (roughly 80 C) after about 8 miles. 

The coolant temperature sender is working fine so I will now try to identify the reason for the intermittent gauge reading. 

Regards,

Michael 

[Magnet]

Thanks Michael,

Sounds like just just took it around the block on your test drive - still, lesson learnt. 
Re erratic gauge:- check sender wiring and connections and give the connection a good dose of contact cleaner. If this doesn’t solve it then treat it to a new quality sender. 
Kind regards,

Gareth. 

[blues1955]

Gareth and other interested persons, I had a courtesy diagnostics test performed today by a local Audi dealer and it was no surprise that the result showed that there was an intermittent problem with the coolant temperature sender. So I asked how it was possible to be able to monitor the coolant temperature constantly using my fault reader connected to the OBD socket. The answer is that the sender generates 2 outputs; one going to the engine management controller (and probably also to the OBD socket) and the other to the temperature gauge.  There is an issue with the temperature sender so I will replace it.

Thanks again, Gareth, for your interest and help with this problem.

Regards,

Michael

[Magnet]

Many thanks Michael,

Um! Possible explanation, but ‘old school’ was that there were two senders/sensors in the coolant system - often screwed into the same area of the coolant system. In that set up, the ‘sensor’ signalled the ECU to adjust fuel mixture etc., and the separate ‘sender’ signalled the gauge. It was not uncommon for these two be confused when ordering, and the wrong one inserted in an attempt to fix a problem.

Yours and one doing both things-? If it (being the only one) is at intermittent fault then why isn’t the mixture set up giving problems as well? Still……

Replacement:- If it were mine, I would not be buying an ‘all sorts’   at best price.  Perhaps Bosch if not using the expensive VAG replacement. 
Kind regards,

Gareth.