1.9TDi AVF Engine engine coolant temperature dash vs climate

[sram]

Hi all

I'm just getting to grips with my A6 C5 Avant 1.9 Final Edition, which I've had for a couple of weeks. I apologise in advance for all of the posts in short succession, but I have found this forum to be the best source of information.
I had what appeared to be a stuck closed thermostat, so I replaced it with what Eurocarparts had to offer. The type of seal was different to the original one, but it seems to be holding fine with no leaks. The engine does seem to warm up quicker now and the coolant gauge shows 90 degrees, but only after it's been driven for half an hour! This seems like a very long time and I've searched the forum to discover that this seems to be a fairly common issue. The temperature of the air coming out of the interior blowers is warm after only 5 minutes of running.
I'm not sure if it's related, I'll mention it just in case, but the oil temperature gauge never really moves past 60-70, even in heavy traffic and when the coolant temperature gauge is slowly but surely approaching 90. Looking underneath the engine it appears that my oil sender is the type that goes into the sump with the three bolts, quite a large rectangular-ish unit.
I played around with the climate control diagnostics yesterday and set it to programme 51 which is supposed to be ECT (please correct me if I'm wrong here). I noticed that when the CC said it was well over 60, the dash gauge did not budge from its lowest position. The CC eventually got up past 100, which I thought was a bit strange, and the dash gauge was still sitting just above 60.
Does the one ECT sensor feed both the dash gauge and the CC unit? It seems odd that the two differ and I know the dash gauge does work because it eventually gets up to 90 after about 30 mins of mixed driving.

Appreciate any suggestions!

[rowdy-999]

If you're getting hot air quickly from the heater, and the engine isn't overheating I wouldn't worry.
Gauges are notorious for being inaccurate.
You could maybe change the coolant temp sensor. Cheap, simple job.

[niall campbell]

The Coolant Temp Sender unit traditionally does the dash and ecu, the radiator fans run off another sensor, usually running off the bottom hose or nearby


Anyway replace the CTS with a genuine one from VW


The dash can be wildly out to what is actually happening in the engine, this can cause fuel consumption to go up as the ECU thinks its really cold ................... default setting to start the car in cold weather

You should get around 640 miles to a full tank of diesel, however in cold weather can drop off to around 540 miles ................................ defrosting car etc


simply replace the CTS and monitor

[Rob69]

Your dash temp gauge should be coming up to 90 far quicker than 30 minutes. My 1.9 tdi passat is up at 90 within 5 minutes or 3 or 4 miles of steady driving, I changed my stat in January as I noticed it taking longer and dipping down when sitting in traffic or turning up the heater. The stat that came out seemed ok and worked alright in a pan of hot water opening at the correct temperature but a new stat improved things a lot, including mpg. The dash gauge is very inaccurate and is heavily damped so the actual coolant temp swings either side of the indicated temperature. If you can get hold of an OBDII diagnostic tool most will show live data which includes the coolant temperature seen at the temp sender, this will let you see how slowly the temeprature is rising and falling as engine load changes. VCDS would let you graph temperature or take a log of data and plot the points. It would also show if the temeprature sender unit itself is faulty.

[sram]

Thanks for the replies.

I will try my generic OBD2 reader and see what it reveals. I wasn't aware I could even use it on this car.

I did pay for a full VCDS readout a week ago, nothing coolant related revealed and that was before I changed the stat.

[bluezie]

Log into the engine ECU with VCDS and look at temp. Then log into instruments and look at temp. These 2 temps are from different sensors, and if closely match can then be assumed to be the exact engine temperature. If not, then one of the sensors is shot.

[sram]

Do you happen to know where the other sensor is and which one handles the gauge and which feeds the ECU and/or climate control diags?

[bluezie]

Do you happen to know where the other sensor is and which one handles the gauge and which feeds the ECU and/or climate control diags?

Mostly in VAG cars, they are a 4 pin dual sensor, ie 2 independent sensors in one unit. Pull the plug and count the pins!

[Col]

On the AVF engine the sensor is mounted into the outlet manifold at the back of the engine. Take the airbox out for easier access.

[sram]

I plugged in my OBD2 scanner this evening and went for a drive. The live data display on the scanner matched almost perfectly the temperature gauge on the dash. The ambient temperature was much warmer today than it was a few days ago when it took 30 mins to reach 90 degrees. This evening it took just over 20. I watched the OBD and dash climb steadily in unison.
Channel 51 on the climate control readout is totally out though - it shows 127 when the dash and OBD show almost 90.

Can someone please confirm that channel 51 is the correct one to use and that their CC diagnostics mode matches (or at least, resembles) the dash gauge?

Thanks