Running cold issue. Tricky one-thoughts needed

[snapdragon]

Originally Posted by ainarssems

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....


OPEN....

[A8L Chick]

Originally Posted by snapdragon

Maybe removing the DPF and catalyst had some effect on running temp.

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

[snapdragon]

Originally Posted by A8L Chick

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

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

[snapdragon]

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.

[ainarssems]

I think there are 2 60A fuses somewhere in footwell

[david@a8parts]

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.

[snapdragon]

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!

[snapdragon]

Technical product information
Engine temperature display fluctuates between 50° and 90° C - all TDI
Customer statement / workshop findings
At outside temperatures under 5°C the engine temperature fluctuates according to the display in the dash insert between 50 and 70°C or till the coolant temperature reaches 90°C. The phenomenon occurs mainly when driving at low engine speed.
Technical background
Because of a very good effectiveness of the engine in low rev range, little engine heat is passed on to the coolant. At low outside temperatures the coolant temperature does not reach 90°C. If the heating is used, the coolant loses further heat depending on the blower level. As a result, the coolant temperature can fluctuate between 50° and 90° C.
Below an outside temperature of 5° C and a coolant temperature of 70° C the standard PTC auxiliary heater is activated, to heat the interior.
Measure
Please do not repair, this is normal.
Customer information
A low coolant temperature has no effect on the service life of the engine. An engine oil with suitable viscosity is used.

[snapdragon]

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.

[brasiliangringo]

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.