NO Heat
 

I have an Audi A8L 2008 model, it does not get warm, temp gauge takes 20 miles to come off stop and therefore car does not get warm, rarely if ever gets to normal, if it does it dives down to 50 c .

Have changed Thermostat and water pump, checked Aux heater is working and it is, lost as to what to do next.

Wow.. I don't think I've ever seen that happen. It could be the coolant temp sensor. I'm not sure but the Climate Control may use data from it to open and close the valve that control coolant flow through the heater core. It's an easy remove and install. It's located in the hard coolant line that crosses from head to head at the rear of the engine. $30 part. Be sure to get another retainer clip as they get brittle and most of time will snap in half when you go to remove them.

Sadly I have already done that, same problem after fitting

Did you bleed all the air out of the coolant system?

Its been like it for about 11 months, didn't worry me during the summer but now it is freezing for about 45 mins, strange this is it comes up to temp for a few mins then goes down again. The Audi diagnostics shows nothing

Hmmm... I'm at a loss... I would think thermostat but you said you've replace it already.

have you checked if the heater core is clogged, or any of the lines?

It will be the coolant regulator. It is an inline thermostat for the gearbox cooler and allows coolant to bypass the ordinary engine thermostat if stuck open.
It is usually mounted in the 1" coolant pipes under/beside gearbox or on some models behind the radiator at the bottom. It is a cheap part circa $15 for a FEBI one as is used on other VAG models.

THanks, that sounds promising, we always thought it was something like that but Audi denied there was a thermostat on the gearbox. I will let you know how it goes. Many many thanks

We have ordered the part, £26 in the UK 33 usd,will be fixing next week, what has thrown us is the fact its not called a Thermostat as you say its a regulator, people in Audi parts had no idea, had to go to a third party supplier who emailed as the coolant system diagram and circled the part.. will update when fitted.