Good afternoon all, 

It's been a while since I've been on here. I'm looking for some help if possible, multiple garages can't diagnose whats wrong. 

The car: Audi A6 C6 2.0 TDi 168bhp - 2010 model - Saloon - 115k Miles

Car overheated one day, no heating at all. Red message saying low coolant or something similar, car was at 110/120 degrees. Booked into a local garage. 

I had the cambelt and waterpump changed as the waterpump had a crack and was leaking.

Collected the car, the second I hit the motorway it did the same thing again, overheated with the red coolant low message. 

Garage said it has to be the the EGR Cooler, new one put on, collected, same message again as soon as I hit the motorway. 

Back into the garage, this time they said we'll change the Heating Auxiliary pump and put on a new genuine Audi thermostat as its probably that.  

New pump and thermostat on, collected, does exactly the same again.  

Cars Routine:

- Cars completely cold, top up coolant, start it up, no message or issues. But no heating at all. 

- Other scenario, I’ve topped up the coolant, run the car, burped the system, then topped up, then closed the cap, spits out the coolant even quicker than usual. I’ve done this around 4/5 times and it takes ages for the coolant to drop. 

- Drive it to work which is around 6/7 miles, mixture of 30mph and motorway. If it goes above 2,000rpm for more than

5/10 seconds whilst in Drive or in gear, I get the coolant message and coolant will spit out of the expansion tank making the coolant level low whilst driving. This took me ages to figure out after multiple stops to top it up. So you're driving, coolants topped up, the cars been driven over 2,000 RPM for a small amount of time or very close to it and you get the message and the coolant will spit out just below the coolant cap. Its not until you stop and look you can tell its been spitting it out. 

- Once I get the message, I stop the car and look under the bonnet, the coolant is below the minimum line and you can see where the coolant has spat itself out in the engine bay. 

- Sometimes I get heating but only when the coolant is low but only on fan speed/level 1 and they have to be on the forward facing vents, anything higher than level 1 and will come out cold. if I switch the fan position to windscreen, you just get freezing cold air, it never gets warm. Everytime I top it up to the max line, I get no heating at all. I only get heating once the coolants been spat out and it’s below the minimum line and I don't top it up. 

- I can have the heating working on level 1 providing I don't exceed 2,000RPM. The second I go over 2,000RPM, it just blows out cold for the rest of the journey. There's no way of getting the heating back. 

- I can drive the car however, I can't drive it over 2,000 rpm or the coolant will spit out and the temperature then starts to raise until the thermostat kicks in. 

- Once the thermostat kicks in, the temperature drops but only once my foot is completely off the throttle and the fans are on the windscreen full speed which is a right headache if you can't stop. It will not cool itself down whilst the throttle is down, you ahve to come off the throttle for at least 15/20 seconds to 60 seconds then it will drop back to 90 again and you can drive again but under 2,000 RPM. 

It's proving to be an absolute nightmare as i'm coming out to the car completely frozen from the weather without any heating. I use 5 to 10 litres of water on cold mornings to defrost the car, then it just fogs up for the entire journey. 

I've spent over £2,000 already trying to get this sorted, I can't just chuck it into another garage and spend another £500 for it to be wrong again. If anyone has any ideas that would be great, many thanks in advance. 

Happy to provide photos if that makes things easier. 

Edited March 3, 20251 yr by A6JP
Added more photos.

Jamie.

Your symptoms suggest there is no circulation in the cooling system, yet your garage has changed the obvious components, so I wonder if there is a physical blockage.

Consider this possibility:

https://www.youtube.com/watch?v=39ngHGvMzEg

It usually only affects the cabin heater, but there is no reason why it can not affect other parts of the system.

Thanks for the suggestion, never knew they had silica gel bags in them. Something to check out. Mine does have some black stuff stuck on the inside the tank, not sure what it is, you can see from the photos. 
 

a blockage sounds correct for how it’s acting, I think the only thing left to replace is the heater matrix looking at coolant diagrams. 
 

I have just driven it home and I had heating on level 1 all the way home but I didn’t go over 1,800rpm to be fair. 

Once I was off the motorway, the heating completely stopped. I use the paddles to get into 7th as quickly as possible to keep the RPM’s low. 

I’ll take a look tomorrow when I’m back from work. Thanks again. 

Edited March 3, 20251 yr by A6JP

I had a look with a good torch last night, could barely see anything in the tank as it’s old and gone cloudy. I topped up the coolant on Sunday and have kept it below 2k RPM since then. Checked this morning and the coolant level is still on the max fill line so nothing has spilled out. going to order a heater matrix and have a go at it with a friend. 

Before spending any money it would be worth confirming a blockage by independantly flushing the heater matrix and the main radiator with water.

Could be, I have no idea on how to do that. I’ll ask some of my mates about doing that before booking it in again somewhere.