Mike Yates

2004 a8 4.2, on the passenger side above the exhaust manifold, runs along side right below the valve cover. I dont have a pic, but ive been having a burnt rubber smell coming from that side of the engine compartment along with slight smoking, it seems to be this hose. What is this hose and is this a common issue? I assume not ive come up with nothing similar in search. Please help

Jack88

Are you talking about the coolant hose? I know that doesn't commonly burn, and I know of no vacuum lines that run there. The hose I'm thinking of is about 1.5" diameter, and goes to the lower radiator y pipe.

Mister Bally

There is a coolant hose that is by the "front two" cylinders. The hose attaches to a pipe that is by the "rear two" cylinders. I don't believe this is your issue. More likely, you have a failed PCV valve that is pressurizing the valve cover area and blowing oil past the valve cover gasket. It will have the burning smell.

I'd replace the PCV valve. Do not waste your money on the $30.00 and $50.00 pieces of Chinese junk sold on the internet. Buy the correct OEM version for $150-200.

All of this is based on internet troubleshooting using your description and my experience. It's better to take the car to someone who is capable of troubleshooting the problem. I cannot troubleshoot this properly without having the car in front of me.

Mike Yates

Thank you for the responses, i just havent had the time to properly diagnose this issue just took a quick look at it. I wasnt ready to really put her on the road as my daily, but i had to due to totalling my truck, so now im noticing these little things. Ill check into the pcv, and i wouldnt dream of putting cheap knock off things on it. Shes got some age and miles on her now, but she was a nearly $80000 car when new, ima treat her right, lol

Mike Yates

Ok ive checked the pcv, taken it apart, cleaned and checked the diaphragm and spring, its like new in there, ive also taken an almost new oem audi pcv from a friends a8 and tried it, im still having the issue. Is there something else in the system it could be? Ive taken and blown into the hose coming into the top of the valve and no air will go in, but with vacuum applied air moves through, the bottom hose has vacuum as it should. When all hoses and pcv attached there is vacuum from the oil filler hole when cap is removed, but not an insane amount.