Information TDI Low/no tempoerature readings. Two A2s with the same issue

Birchall

Dick Chown Award 2016
#1
Two of the cars I have bought recently (both TDIs) suffered from pretty much identical problems and it wasn't quite what I expected.

Both had temperature gauges that hardly moved off the 60 degree mark.
So I immediately thought it would just be a broken temperature sender.

I replaced the sensor on the first one and it made little difference so I jumped to a conclusion that the new tempo sensor was faulty (that happens more often than you would think), but no, even after another sensor change the problem persisted.

So there was only one culprit left, the thermostat. I must admit that I didn't think it could be that because if the temperature sender was working correctly it means that the engine was running at 60 degrees or less, even at motorway speeds (I know these TDIs don't give off a lot of heat, but not getting above 60 degrees, even under load???

I carried out one final test, I did the same run, but this time leaving the climate switched off (the theory was that with the climate on the electric fan runs regardless of engine temperature, so switching it off should see an increase in temperature. Sure enough the needle did start to rise and it hit 75 degrees.
To me that proves that the temp sender had NOT died completely at least.

So it did seem to point to a thermostat problem, so that was changed.

FIXED !!! The temperature rose to 90 (where it should be) quite quickly and stayed there, as it should !!!!

A few days later the other TDI (which I thought had a temp sender issue too) acted the same on a run with the climate switched off, the temp rose a little.

So today the thermostat was changed on that one and hey presto, a perfect temperature of 90 quickly showed and stayed there.

So if you have a TDI that is acting like the sender has failed, try the same check, switch off the climate and see if the temp rises. If it does, you have a failed thermostat. They are reasonably cheap and pretty easy to replace on the TDI AMF engine at least. They are in the front and the alternator mounting is slightly in the way, but it is a DIY job.

I hope this helps if you have similar issues.

Steve B
 

mrbroons

Active Member
#2
Had the same issue on my 1.4i, same answer although in my case it was also a missing rubber gasket as 2 were given but i had 1 installed as the other was deemed a spare, nope both are required. Easy fix but took a while.
 
#3
That's interesting. I have the same issue on my TDI. Temperature sender was replaced during a cam belt change but it still reads low.
Is replacing the thermostat a job I need to do now? Will it cause problems if I leave it for a month or so?
 

Birchall

Dick Chown Award 2016
#4
That's interesting. I have the same issue on my TDI. Temperature sender was replaced during a cam belt change but it still reads low.
Is replacing the thermostat a job I need to do now? Will it cause problems if I leave it for a month or so?
If the car is running OK then you could wait a while, especially since the weather is warming up (a little)

I wouldn't leave it much longer than 4 weeks though. The thermostat is on the front of the engine and it is a pretty basic one too, so the cost should be low.

Steve B
 
#5
Had exactly the same problem about 6 months ago, it was due a cambelt change anyway so i asked them to change the Thermostat whilst they were there.
 
#6
Thanks Steve - got the same problem with ours. Tried turning the aircon off (for several minutes) but the gauge still showed just over 60 degrees so it should be just the sender.
 

Birchall

Dick Chown Award 2016
#7
Thanks Steve - got the same problem with ours. Tried turning the aircon off (for several minutes) but the gauge still showed just over 60 degrees so it should be just the sender.
The increase in temperature is not quick, I was doing motorway miles and after about 5 miles it started to creep up.

The TDIs run surprisingly cool and so temperature changes take time.

So before you spend on a sender try a longer run and even a small increase in temperature might indicate a thermostat issue.

Steve B
 
#8
Stupid question but how do you turn the aircon on & off? Mine didn't come with a manual

Sent from my ONEPLUS A3003 using Tapatalk
 
#9
You can turn it off and on by pressing the "ECON" button Craig... if the orange or red light is illuminated on that button then the air con is "OFF" or running on an increased economy mode. If the orange light is off then its running at its full capacity, ie "ON", and should be super cool with a "lo" temperature setting.
 
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Birchall

Dick Chown Award 2016
#10
Stupid question but how do you turn the aircon on & off? Mine didn't come with a manual

Sent from my ONEPLUS A3003 using Tapatalk
Pressing the "off" button at the bottom of the climate panel is the best way for this test.

By using that you are also not cooling the water down by blowing heat through the heater matrix.

You are aiming to conserve as much heat in the engine as you can to try to get the temperature up high enough to register on the temp gauge.

Steve B
 
#12
Two of the cars I have bought recently (both TDIs) suffered from pretty much identical problems and it wasn't quite what I expected.

Both had temperature gauges that hardly moved off the 60 degree mark.
So I immediately thought it would just be a broken temperature sender.

I replaced the sensor on the first one and it made little difference so I jumped to a conclusion that the new tempo sensor was faulty (that happens more often than you would think), but no, even after another sensor change the problem persisted.

So there was only one culprit left, the thermostat. I must admit that I didn't think it could be that because if the temperature sender was working correctly it means that the engine was running at 60 degrees or less, even at motorway speeds (I know these TDIs don't give off a lot of heat, but not getting above 60 degrees, even under load???

I carried out one final test, I did the same run, but this time leaving the climate switched off (the theory was that with the climate on the electric fan runs regardless of engine temperature, so switching it off should see an increase in temperature. Sure enough the needle did start to rise and it hit 75 degrees.
To me that proves that the temp sender had NOT died completely at least.

So it did seem to point to a thermostat problem, so that was changed.

FIXED !!! The temperature rose to 90 (where it should be) quite quickly and stayed there, as it should !!!!

A few days later the other TDI (which I thought had a temp sender issue too) acted the same on a run with the climate switched off, the temp rose a little.

So today the thermostat was changed on that one and hey presto, a perfect temperature of 90 quickly showed and stayed there.

So if you have a TDI that is acting like the sender has failed, try the same check, switch off the climate and see if the temp rises. If it does, you have a failed thermostat. They are reasonably cheap and pretty easy to replace on the TDI AMF engine at least. They are in the front and the alternator mounting is slightly in the way, but it is a DIY job.

I hope this helps if you have similar issues.

Steve B
Thanks Steve this worked very well. As I am new to the A2 and Tdi I didn't know what temperature to expect but it was always reading on the bottom half of the scale (60-80 degrees).
Replaced the thermostat and all is now working fine with a solid 90 degrees showing.

Mickey
 

Paulus

A2OC Donor
#13
Hi Chaps and Chapesses!

Our lovely 2001 A2 1.4tdi had same problem and our cambelt was due a change, so water pump and new thermostat added at same time. Temperature then remained stable at 90 for a week, but then started dropping to 60 and stayed there. Switched climate off at lower middle switch, temp climbed to 80, eventually, then cycled between 70 & 80 on journey home. Am I right in thinking that this is either a faulty new stat, or the actual sensor playing up? I am taking car in today and I think he wants to change the sensor. Happy Summer Days y'all !
 

Birchall

Dick Chown Award 2016
#14
It does sound like the sensor may well be the fault. BUT it could even be that the thermostat might have been faulty.

Both items are reasonably easy to change so try a new sensor first. Then if that doesnt resolve it I am afraid it is likely to be the thermostat that has failed (new Ines do sometimes have a fault) it is also worth getting the mechanic to check that the thermostat is fitted correctly and has used the correct rubber seals (rings)

steve B
 

mrbroons

Active Member
#15
I had the same issue. Was the thermostat. There are two o-rings supplied, both must be used or you get the issue you describe. My garage installed 2 stats before realising the second o-ring is not a spare like on other stats they have seen but actually required for a proper seal. Now all working perfectly.
 

Paulus

A2OC Donor
#16
Good morning Steve & Mr Broons,

Thank you for replying so swiftly, I appreciate that. I have just got back from leaving the car back at the garage for them to sort out, but I will phone the boss with your comments. I did actually read both of your earlier entries on the forum (like a good boy!) as its frustrating when the answers are there but some find it easier to plunge in and start a new thread. Mr Broon's comment about the O rings is interesting. Do they go either end of the stat when it goes in? I will quiz the mechanic. I have also had the door locking / unlocking when the ignition is switched on, but curiously seems dependant on whether my seat belt is clipped in or not. If its not, I don't get the clunk click. Out of habit, and sympathy for the car, I always depress the clutch before starting, to take the gearbox load off of the starter, an old school trick. Just made me wonder if instead of of the comfort computer packing up, as suspected in many posts, operating driving controls in certain sequences triggers a self diagnostic cycle ? Just musing, really. Again, Gentleman, thank you for your input , really appreciated, I love this club, its just fortunate that I don't need to look up problems on it so much as our car is usually great. cheers, Paul (that's my wife, Fizz in the profile picture, not me, she looks far nicer than I do, lol)
 

Paulus

A2OC Donor
#17
Good morning Steve & Mr Broons,

Thank you for replying so swiftly, I appreciate that. I have just got back from leaving the car back at the garage for them to sort out, but I will phone the boss with your comments. I did actually read both of your earlier entries on the forum (like a good boy!) as its frustrating when the answers are there but some find it easier to plunge in and start a new thread. Mr Broon's comment about the O rings is interesting. Do they go either end of the stat when it goes in? I will quiz the mechanic. I have also had the door locking / unlocking when the ignition is switched on, but curiously seems dependant on whether my seat belt is clipped in or not. If its not, I don't get the clunk click. Out of habit, and sympathy for the car, I always depress the clutch before starting, to take the gearbox load off of the starter, an old-school trick. Just made me wonder if instead of of the comfort computer packing up, as suspected in many posts, operating driving controls in certain sequences triggers a self diagnostic cycle ? Just musing, really. Again, Gentleman, thank you for your input , really appreciated, I love this club, its just fortunate that I don't need to look up problems on it so much as our car is usually great. cheers, Paul (that's my wife, Fizz in the profile picture, not me, she looks far nicer than I do, lol)
 

Paulus

A2OC Donor
#18
Hi again, Steve and Mr Broon's,

Just rang the garage re oil filter O rings saga, they have just done a diagnostic test and the readings on the their machine show temperature correctly, but the dash temp meter is not reacting to the circuit reading and is therefore an electrical fault. They say that this was very common on the TT's and basically the dashboard had to be changed. Have you heard of this? He says its fine to drive as its working correctly, its just that we won't be able to have the peace of mind of seeing it on the gauge. cheers, Paul
 

spike

Well-Known Member
#19
While a common problem on TTs, I don't recall anyone ever needing to replace the instrument cluster on an A2 for this reason.

Low temp reading is usually down to a faulty thermostat (which you have changed) or most likely, the dual circuit temperature sender. One circuit provides a signal to the engine ECU - which according to the diagnostic test is reading normal. The other circuit feeds the temp gauge, and this quite often fails, giving a low reading.

Cheers Spike
 
#20
While a common problem on TTs, I don't recall anyone ever needing to replace the instrument cluster on an A2 for this reason.

Low temp reading is usually down to a faulty thermostat (which you have changed) or most likely, the dual circuit temperature sender. One circuit provides a signal to the engine ECU - which according to the diagnostic test is reading normal. The other circuit feeds the temp gauge, and this quite often fails, giving a low reading.

Cheers Spike
seconded Spike I have had exactly this issue in the past