Thermostat Temperature

[daedalusminos]

Well I'm enjoying being a new A8 owner, but unfortunately it looks as if the thermostat is playing up (temp gauge creeps up, but drops back with interior heating on full).

Reluctant to pay approx £35 from an Audi dealer, I decided to go the local motor factor route, but does anyone know the correct opening temperature? It would appear 80-88C are listed and even the local Audi dealer was unable to confirm the temperature.

Jonathan

[M-A8]

Jonathan,

We do like an introduction first in section just for it with some photos.

http://forum.a8parts.co.uk/forumdisplay.php?f=4

Secondly, being reluctant to pay £35 for original part in my opinion isn't the smartest move especially that the entire front end needs to come out inc bumper, radiator with frame, v belt and cam belt....if thermostat is the problem of course and if it is and cam belt is due then new tensioners, pulleys and water pump would be recommended - cost close to magic 4 digits with this cars if you take it to the garage....now thinking about it, this must be another reason for 4 rings in Audi badge oooo look very close to £1000 bill for each visit at the garage.

[David's8]

Intro would be good especially as you are claiming a bit of greek and maybe royal heritage. Are you related to Prince Phillip by any chance?

Dont know what the D3 operating system requires but with a D2 its 90-92degC.
You may find the attached useful tho' it doesnt answer your question but there is lots there of interest.

[mattylondon]

I agree with Marcin, pay the extra few quid and get it from Audi / TPS. In the overall cost it's only a slight % more. Are you going to change all the belts while you've got the front removed?

[daedalusminos]

Many thanks for replies. I'll post an intro with pics....need to take pics first....

The timing belt, water pump, idlers and tensioner were replaced 3yrs (21,000 mi) ago, unfortunately it looks as though they didn't replace the thermostat so it's probably still on the original (74,000 mi). Therefore this thermostat has only got to last a couple of years.

As I understand the thermostat can be replaced without 'removing' the timing belt, and there appears to be loads of room compared to some I've worked on in the past.

Thanks Matt, 87C sounds about right, the gauge sits at 90, but it's obvious there's a fair amount of 'signal conditioning' applied to the temp sensor to eliminate a wandering needle.

Where's my camera...

Jonathan

[mattylondon]

I have seen the thermostat replace with just slacking the cam belt. I guess you would still need the crank pin and cam locking bar when torquing it up again? But I suppose if you're DIYing yourself it should be ok and then replace the other parts at another time.

Just out of interest, what actual peak temps are you getting?

[daedalusminos]

The gauge used to sit and stay spot on 90C, about a week ago I noticed it rising, it got to 110 then started to drop again. I pulled over, switched off and switched ignition back on straight away and strangely the gauge was at 90 (I estimate it should have read approx 100).

Now when driving from cold it seems alot longer to come up to temperature, it will then stay at 90 for a while then start to creep up, at which point I put interior heating on full and open a window and the gauge drops back to 90.

When I stopped with the gauge over 90 the rad fan was on, but it was just pumping cool air out...I suspect no (or little) hot water in rad.

Jonathan

[JulianHicks]

Originally Posted by daedalusminos

The gauge used to sit and stay spot on 90C, ...

Jonathan

All VAG instrument panels tell fibs They are all programmed to show 90degrees exactly within a range of about +- 10 degrees. That is they show 90 at all temperatures between 80 and 100

I've seen this 'fib' myself running VCDS monitoring the Engine ECU [which is where the temperature sensor sends its info]. So you can't trust what the guage says when you're having problems

Julian

[JulianHicks]

Originally Posted by daedalusminos

Reluctant to pay approx £35 from an Audi dealer, I decided to go the local motor factor route, ...

Jonathan

Others may correct me, but the A8 thermostat [at least for the V6 3.0 TDi] comes in a housing, so £35 isn't too bad. Note that Halfords quote £100 for an A8 thermostat and my local branch of Euro Car Parts quote £80. I haven't got a local Audi dealer so went to ebay and got a Gates one online for £35 delivered [not installed yet though].

There are conflicts about what needs to be done for thermostat removal. Some Audi docs [the 'timer units' one for workshop quotes, for example] quote over 4 hours because the 'cage' has to come out but other manuals [engine workshop manual] suggest it can be replaced by being careful with the water that comes out and just needs the belt cover removed and the housing undone from the block. [This info. as per the 3.0 TDi instructions].

Suggest you look for the Audi workshop manual for your engine elsewhere on this forum.

Julian

[daedalusminos]

Ok, just thought I'd post how this 'ended'.

Getting to the thermostat was relatively easy:
No need to jack car, though it would make it easier to replace under tray.
Remove engine under tray (turnbuckles - 3 front, 3 rear and 2 each side in front lower wheel arches)
Drain block LH: drain pipe runs down LHS of engine to sump level. Remove expansion tank cap to allow max drain - expect about 5litres.
Move drain container to front of engine ready for a small amount from behind thermostat cover.
Remove timing belt covers
Remove 4 bolts and loosen one behind RHS cam wheel to allow pressed metal TBelt backing plate to be swung up.
Pull Tbelt half way off RHS cam wheel (use cable ties to ensure it doesn't come all way off)
Loosen and remove 3 thermostat housing bolts (prepare for small amount of coolant loss)
Pull housing forward and slide up allowing thermostat and O-ring to be removed.
Reverse procedure to replace. Don't forget to remove cable ties!)

L/RH as seated in driving seat.

Important points: the thermostat I purchased from local motor factors was INCORRECT! The correct thermostat is 67mm, 82°C (the bypass valve flap was also the incorrect diameter)......in the end I went Audi genuine part.