Gauges not moving

[tombad]

Hi all.
I have an Audi A4 b5 1.8T (1999).
I have an issue with the temp gauge and oil gauge not moving off the bottom mark even though I have done the obvious jobs as follows:

I recently changed thermostat as the car was running cold when moving and warming up to 90 when at rest. This went fine and temp gauge worked ok afterwards. (Oil temp looked low at around 90 degrees but guessed this might be OK as matched water temp).
I then had the waterpump changed as it was knackered and rattly. This also went fine and all was well afterwards.
Then one morning I noticed water temp and oil temp gauges were both not moving at all. I checked the ECU temperature off the climate control panel and it went up to 90 and sat there as expected.
I therefore changed the temp sender at the back of the head for a new green one which made no difference. Gauges still don't move.

Please can you tell me what other sensor or part may be responsible for this behaviour? The Speedo, Rev and petrol gauge are all fine. The screen in the middle of them has some lines on it, but always has.

Any advice would be appreciated. Is the Multi Function Temp Sensor (MFTS) anything to do with this?

Thanks,
Tom

 

[aragorn]

Temp sensor at the back of the head does both the ECU and the dashboard readouts, so you've already changed the one sensor that could affect coolant temp.

Did you use channel 49 or 51 on the Climate?

51 seems to lie, so use 49 for an accurate readout.

 

[tombad]

I used channel 51. Will give 49 a go tomorrow.
On channel 51 it climbs nicely up to 90 - can take about 20 mins in this winter and then locks onto 90 and never moves. I presume its overridden just prior to and after 90 so that your gauge stays dead centre.That sensor does not explain why oil temp gauge also stopped on the same day. Would have thought (hoped) that both oil and coolant gauges wouldn't die on the same day so must be a common fault. So what does the mfts do?
Thanks for help so far.

 

[aragorn]

ye thats the problem, 51 will show 90 when its nothing of the sort.

Perhaps the new stat is broken and the temp is simply very low?

I had a new stat seemingly fail a few weeks after changing a water pump, and upon replacing it i found a small shred of plastic presumably from the pump impeller had wedged itself inside the stat, wedging it open.

Never heard of a MFTS? The car has the dual temperature sensor behind the cylinder head, and thats it.

 

[tombad]

Hi.
OK, so I tried channel 49 today and sure enough it read totally different to channel 51. (I thought channel 49 was "Malfunction counter for speedometer (vehicle speed) signal".... anyway). Channel 51 seems a bit pointless.
So over a 25 minute journey of country roads (on which I tried warm up the car as best I could) I only managed to get to 61 degrees which also happens to be the bottom mark on the gauge so it doesn't move! So that certainly leads me to think the new 'stat has malfunctioned already. However, I then left the engine running to see if it would then creep up to 90 eventually but what actually happened was that it got up to 67 (and sure enough, the gauge just started to show movement) and then at 67 the main fan cut in and started cooling it down and the temp dropped back to 60odd .... and then I gave up watching! I opened the bonnet and grabbed the radiator top hose to see if it was anything like 90 degs and it was warm but not uncomfortable to hold... like about 61 degs I reckon.

So I guess I have 2 further problems to fix, another thermostat (mine was from gsf) to replace the new one. (Is that a common thing?) and also the sender that tells the fan to kick in. Is that the one in the top of the radiator or the one in the bottom?

Any further advice welcomed!

 

[aragorn]

The fan might have just kicked in due to the climate control? If the AC had engaged it would have fired up the second fan.

I got a "Topran" stat from AllGermanParts and it seems fine.

 

[nwmlarge]

i have a sensor assembly attached to my sump. would that have anything to do with it?

 

[aragorn]

That measures oil temperature and oil quality.

Theres nothing wrong with his guages, the are accurately reading the oil and water temperatures.

His thermostat is jammed open meaning the engine is being over cooled.

 

[tombad]

The fan might have just kicked in due to the climate control? If the AC had engaged it would have fired up the second fan.

Yep spot on. I set the climate to econ and repeated the test and eventually got the car up to 90 on the gauge and climate display. That new stat must be jammed totally open. What a PITA. Thanks for you help aragorn! Time to get that belly pan off AGAIN and have a coolant shower.

 

[nwmlarge]

do you not just do the stat from above on yours ?
i undone and removed the boost pipe and then did all of mine from above.

 

[aragorn]

I suspect yours is an 06A block (AWT engine code). these have the stat mounted on the side of the block just under the inlet.

Toms is most likely an 058 block, which has an external water pump and the stat is right down the bottom beside the PAS pump.

 

[nwmlarge]

that makes more sense.
i did wonder why all the guides a read were wrong.

i've taken pics and will get round to doing a guide for AWT specific stats.

 

[N22CKS]

Iv got this exact same fault on my 1999 1.8t A6. I fitted a green sensor with no joy, so im going to fit a new thermostat and hope for the best!
My temp guage has a reading when i start the ignition but it then drops off to 60 as i drive.
Hope the thermostat is the cause.
Iv taken a deposit on the sale of my car and he wont pay the balance until the gauges work so fingers crossed!
Thanks

 

[mal79]

Damn coolant circuits... Have same problem with temp gauge. In Jan 2010 changed the stat, temp sensor and water pump with GSF parts. Temp gauge showed correct for a few months but then back to its old tricks of not moving off of 60 deg C. I was thinking it might be the sensor so was ready to get an Audi part when, stuck in traffic I saw the gauge move a little off of 60 deg C.

So did the climate panel test on channel 49 and during normal driving the temp was about 52-56 deg C. Switched off the air con and waited...waited...waited some more - eventually got to about 68 deg C and the gauge had moved by similar amount. Sensor is fine then I think, so must be faulty stat...

Yesterday replaced stat with Audi part and after about 20 mins of idle/ fast idle channel 49 tells me coolant is 30 deg! Cant warm it up with a proper drive just yet as found that CV boot clip has detached and joint is exposed again (must crimp it properly this time...). That said rad top hose did seem pretty warm by the time I called it a day, though didn't feel bottom hose as had put undertray back on.

Just tested GSF stat in a pan of boiling water and it opens at EXACTLY 87 deg C as per my multimeter thermometer. Granted it doesn't fully close until 77 deg C but the spring did look a bit weedier than the new Audi stat. Anyway assuming that the stat was OK all along, and the new stat is also opening, then I guess I am back to either a faulty sensor or a persistent airlock right about where the sensor is.

Any thoughts?

 

[nwmlarge]

sounds like the same fault as mine had, which was a stat jammed, swaped it out problem solved.

it must be an air lock if your stat is working

 

[mal79]

Now I am pretty sure it is the temp sensor. Had the engine warm today, channel 49 shows 30 deg C at cold and gets to about 36 deg C after 10 minutes. Of course there was no movement on the gauge. No amount of squeezing the top and bottom rad hoses changed this.

I decided to test the actual coolant temps with my trusty multimeter. First off tested the surface temp of the hoses and pipes by the heater matrix - hoses were about 40 deg C and pipes over 50 deg C. Next I pulled the coolant temp sensor and coolant directly below was 77-78 deg C. This seems to be confirmed by the bottom rad hose warming up after a while indicating that the new stat is opening as it should allowing the cold coolant in the hose to enter the engine and being replaced with the warmer coolant from rad.

I was surprised that there was no coolant trying to escape when I removed the temp sensor, the level seemed to be a little below the sensor. Given the design of the take off (vertical "Y" pipe about 2 inches in height) I figured that this would be a good location for an air bubble to form and the sensor could be trying to read temp of warm air. Topped up this pipe with a bit more coolant to make the sensor read coolant temp. After some more driving, channel 49 still reading about 36 deg C. Didn't even bother to test the coolant again...

Anyway a couple of questions. The temp sender I have is bright blue, though I thought it was supposed to be green on 1.8 petrols (ADR engine)? Secondly, the "Y" shaped take off had the temp sender in the left outlet but the right outlet had a blanking plug in there. Does another sensor usually go there?

Mal

 

[aragorn]

The other port is for the Aircon sensor, preusmably your car doesnt have AC.

Fit a genuine Audi sensor and see what happens.

 

[mal79]

I'll get the OEM sensor ordered today. Hopefully once the engine knows the correct opperating temperature, then it will run a bit better (warm starts etc). Then I can get the oil and probably plugs changed.

Its strange about the other take off being for air con as I have fully functional climate control. There was no sign of an unused plug, so I guess the climate control is getting coolant temp from elsewhere?

 

[aragorn]

Hmm weird then, i always thaught thats what the second port was for.

I'll have a look on my engine later on and see if its the same.