Running cold issue. Tricky one-thoughts needed
 

My silver '8 has been running a little "cold" recently. I originaly thought "ok, time for a new thermostat, water pump & belt".

I had the above sorted yesterday using all OEM parts and the problem still persists. Mainly during motorway use, and it seems to run even cooler when using the a/c cc.

I have no problems with heat in the car, heaters work just fine, no water leaks, water levels are fine and system was bled properly, taken for a warm up run and then re bled to be safe.


The needle isnt jumping around arratically which makes me think it's not a temp sender fault. Could anyone point me in a few directions of other parts that could be to blame for this odd temp behaviour. :-(

Bex

not sure bex but love the new sig pic! +++

Awesome sig pic, not sure about the engine. Ben/Mike/Physce/A8Doc will probably know.

Could still be temp sender, but if it's going to a normal place whilst idling/town traffic, and then dropping when going fast, it may not be.

Maybe the fan staying on when it shouldn't. Does it behave with the climate off or set to econ mode?

Thanks for the sig comments chaps +++ :D I have a few new pics I rather like. ;)

Yes I think it does go back to the normal 90 (middle of dial) during town driving.

I will confirm later but I am pretty sure that when using econ, temps remain normal.

I will update a little more tonight after work. +++

I was thinking the fan may be staying on-but I cant hear it when I pop the bonnet :Confused:

Can you put VCDS on it and check the temperatures from the senders.
The drawings show you have twin electric fans. If one were not switching off that might cause the problem. But running cold usually means thermostat issues of temp sender issues.

Hmm, ok maybe I ought to think about ordering a new temp sender, it goes up and down so gracefully that I really don't think this is the culpret :(

I will try to get plugged into VCDS later. Not sure whether the guy will know how to access the temps from the senders.

Could you advise on how to access this in VCDS?

Just to add, I am going over to my friend with VCDS within the next 2 hours, and he has asked whether anyone knows which number measuring blocks are for the temp senders?

That probably means more to you guys than to me :D

just cycle through the ones for the engine as they may be different from my PF D2.

Temp readings seem normal on idle, couldn't test it running at higher speed (when it actually runs cold) because the laptop battery doesnt hold its charge and has to be connected to the mains constantly.

:( I am going to order a new temp sender anyway. I will keep you all updated +++

If it runs OK standing and low speed but cold at high speed only thing that could be wrong is thermostat stuck open.

I guess you didnt read the whole post.

It has a new OEM thermostat and water pump fitted. Thermostat is working perfectly.

Did the fitter test the thermostat in a bucket of hot water before he fitted it in time honoured fashion. New parts can go duff! :rolleyes:

thermostat tested and working correctly +++

Then that only leave the pixies and a sender!:D

Knowing my luck...it'll be the pixies :ROFL:

Engine running cold
 

Do these have a viscous fan cos that can sometimes cause the engine to run cold....the only other thing that ever caused an issue for me was a poorly sealed rocker cover on an old e36....but to be honest the only things that can normally cause it are thermostat or viscous fan

Hello folks! Did you get any further forward with this A8Chick?
I have the same problem.

My 2006 3.0TDI A8 is rather slow to warm up, and never seems to get to 90˚c in fact it seems happier at 60-70˚c.

I replaced the thermostat with a genuine one as I know these are known to stick open, no change.

Next I replaced the G62 coolant temp sensor to no avail.

The Webasto is working fine and I am manually turning it on, but still running cool.

The heaters in the car get warm but not hot like my old passat which suggests it really isn't getting warm, but could be a red herring.

Any tips? TIA.+++

is the fan on all the time or too much? temp sensor for the fan could be making it overcool the system?? :Confused:

I went for a run today was running very cool in this weather.
There is no viscous fan, but there are two well caged and shrouded electric fans and these are both running continuously (abet slowly) from startup, except with the climate control completely off.
VCDS shows that they are being told to run by duty cycle, and the Engine output tests speed them up and down correctly.
Group 7 also shows oil temp and this a few degrees higher as expected but still cold like the coolant.
It would appear that there is only one simplex (two pin grey) coolant temp sensor on this engine.

019 Fan activation\
1) Coolant temperature\
[\'b0C]\
2) Air conditioner fan activation\
[%]\
3) Radiator fan 1 activation\
[%]\
4) Radiator fan 2 activation\
[%]\

http://dl.dropbox.com/u/1273965/fan%20status.PNG

Unfortunately I can't help yet as I still haven't sussed this :-(

As far as I can tell only reason for running cold is faulty thermostat. If the thermostat is working correctly coolant does not go through radiator and fans can work at full blast it will still warm up properly.

Another possibility is that it is just reporting temperature incorrectly. Not sure about 3.0 TDI but many cars have several(2) temp sensors.

You are right, the radiator is getting warm, and it shouldn't when the engine is not reaching the 84˚c marked on the thermostat.

Today, I cleaned the engine and went for a blast in the countryside in sports mode to dry it out. The gauge never went past 60˚C and was happier at just 50˚C.

When I got home and opened the bonnet it was barely lukewarm, not the usually heat radiation you feel on your face from healthy cars and some parts such as injector pipes were stone cold. I used an infrared thermometer to check various parts of the engine, the hottest were about 57˚C apart from the EGR pipe and turbocharger shield which aren't cooled. If it was the water pump, it would definitely overheat and I think would show a high temp on the gauge as the coolant temp sender is in a place where this would be detected.

The engine looked very clean, finished a few bits off with brake cleaner and used some Tectane engine lacquer. Looks like new now.+++

I think I'll buy another thermostat, it's a simple 15 minute job the second time round.

I'll return the old one if it makes a difference. I know I could test this one in a bucket of scalding water, but with the slight hassle of removing it, I'd rather just put a new one on while it's off as it was quite cheap from TPS.

My other car (Focus) was running very cold the other day and giving pathetic output from the heater, so I had the thermostat replaced which fixed it.
(didn't do it myself and had a few other minor things done at the same time by my tame mechanic)

But looking at the old thermostat you could see that the central moving part was not moving true and was catching on one side on the body.
I did some tests with boiling water and discovered that it was basically catching so staying stuck in one position, though it could be freed by wiggling or a rapid temperature change.
I suspect it had been misbehaving for some time but it needed a nice cold snap to make it obvious.

Well. I don't know what it can be. I bought another thermostat today and thoroughly inspected and tested it in a saucepan. It opened when the water was about 90*c. I just fitted it after work and refilled and bled the coolant with the 3 bleeding points. Tested the old one. Just the same as the new one in the pan. Went out for an hour run and took ages to warm and only reached 70*c as with the original and first new one.

I will do more tests tomorrow and try disconnecting the fans.

If they are viscous fans then maybe the viscous coupling is faulty and sticking the fans so the blades are always rotating :Confused:

In the past when I've has a viscous fan seize up, in other words it works full on all the time - hot or cold, then you get a lot of fan noise when you rev.
Normally the fan will semi idle when cold and only begin to lock up and spin with the engine when it gets warm or hot.
Have a listen

Thanks. I still haven't done much testing of the radiator temp to see if it gets warm too early, because a) it's hard to get to any part of it and b) it is usually raining or dark when I drive.

There is no viscous fan on this model, just two electric ones which run at ~12% duty cycle from the word go. I haven't yet found if this is normal, but for comparison, I read on an A4 forum that it is normal for one to run all the time unless outside temp is under 5˚C.

New genuine temp sensor fitted last night, but still never got over 75˚C in over an hour of urban driving in sport mode.

Just a guess- maybe it is getting twisted/squeezed when fitted in housing which restricts free movement?

Also once the thermostat I tested in boiled water seamed to work correctly and I only noticed that it is not closing properly later. It was hard to see because of the shape but it always stuck little open about 1.5mm but what are the chances of it happening with 2 new thermostats.

Thanks, this is a thermostat that comes as part of a larger plastic housing with outlet pipe to radiator. I suppose a bit like the metal housing of the older V6s but with the thermostat built in. When it was closed it was air tight, I could put the pipe in my mouth and blow until my eyes popped out.
Once hot I could blow easily.

The second time round, I was very careful on fitting (which is quite easy anyway), such as not to knock the moving parts.

I'm now starting to think this is normal for a modern diesel.
Maybe removing the DPF and catalyst had some effect on running temp.

Next, I will try disconnecting the radiator fans and if that doesn't work I can't see what else it could be, as it runs like a dream, so I can't suspect retarded injection or anything that drastic.

CLOSED....
http://dl.dropbox.com/u/1273965/IMG_2224.jpg

OPEN....
http://dl.dropbox.com/u/1273965/IMG_2222.jpg

If it helps-mine was running cooler before DPF removed... :Confused:

Yes, it is helpful thanks, +++ it shows it probably isn't that.

Hello folks.
I still have this running cold issue.
The Webasto can still be on after an hour of spirited driving and the guage shows about 60˚c and the engine feels cool.

In addition to the stuff I already did, I have increased the coolant concentration to the maximum permitted of 67% (to reduce the heat capacity).

I now want to disconnect the electric cooling fans.
I removed fuse 5A in position 17 to no avail, the fans kept running, I think because the fuse is 5A it is just for the control module.

Does anyone know where the power supply connector is for the fans? I have read a post about a 4.2 TDI which said on top of the radiator, but I can't see anything other than the microswitch connectors for the bonnet catches.

Any help disabling the fans as a test would be greatly appreciated.+++

I think there are 2 60A fuses somewhere in footwell

There should be a pair of beefy connectors - one for each fan - on the fan housing panel itself. Looking at a reference model here the offside one is above the fan and the nearside one is underneith. These connectors slide apart but they are fairly tough to seperate.

Thank you both, I can see the top one now with a torch at night. It's always easier than in the sun.

I will look for the fuse panel as that may be easier in some respects.
I can't get it unplugged tonight as going into bodyshop for a couple of days so will report back in a few days. Cheers!+++

Woohoo.
After 4 years of cool running temp and webasto constantly running...
I found there is another hidden (above driveshaft UJ and behind chassis) thermostat on all A8s, on some near the radiator and some on the side of the gearbox. It regulates coolant flow to the gearbox. If this thermostat is stuck open it means coolant circulates the whole system from cold and never warms up unless it is hot outside.

It is a common part reference and point of failure across many VAG models.

FEBI 38713
VAG 4E0 121 113
Thermostat, coolant ~ £20

Part has arrived so will fit it on monday.

One thing that does puzzle me is what is the wire clip for - it is hard to get to the thermostat but there is a spring clip on each hose and the wire clip looks redundant.

A simple verification for the thermostat is to place the old and new in a pan of water and heat on the stove and u shld see an obvious difference in opening times as the water comes on to the boil or circa 87 degrees being pedantic.