Odd Smell from Car While Driving

Faulty Hose Composition leads to Smelly Audi A4 Quattro wagon 

Noticed an odd smell from the car, so he stopped at a shop to get it checked out. He was told that the coolant reservoir was cracked and needed to be replaced. Not satisfied with this diagnosis, he later drove to our shop. We performed a pressure test on the reservoir and discovered that the hose between the coolant reservoir and the engine was weeping coolant through the hose material.

If the coolant reservoir appears to be leaking, the technician should also check these possible leak sources before replacing the reservoir.
May be caused by the coolant hose (1) between coolant reservoir and radiator or the coolant hose (2) between coolant reservoir and engine which may have internal cracks (Image 19-A116).
Internal cracks can cause coolant to get inside the coolant hose material and leak from connections to the coolant reservoir (arrows) due to the capillary effect.

The following tools (or equivalents) are required to complete the diagnosis: VAG1274 Cooling System Tester, VAG1274/8 Adapter and VAG1274/9 Adapter.

Applicable Vehicles:
2001 to 2006 All Models, All Engines

Repair Procedure:
(Review safety procedures in the ALLDATA ® system before beginning)

Before replacing coolant reservoir:
Check if coolant hose (1) between coolant reservoir and radiator is leaking at connection to coolant reservoir (Image 19-A116).
Replace that coolant hose if necessary.
Run engine or drive vehicle until coolant reaches a temperature of 80Run engine or drive vehicle until coolant reaches a temperature of 80°C (176°F).

Coolant reservoir, checking for Leaks:
Remove filler cap on expansion tank.
Install tester VAG 1274 and adapter VAG 1274/8 shown in diagram (or equivalents) on expansion tank.
Build up a pressure of approx. 1.0 bar with hand pump on tester
If this pressure is not maintained:
a. Trace and repair leaks.
b. Check if any coolant leak around coolant reservoir still exists.

Pressure relief valve in filler cap, checking:
Screw filler cap onto tester with adapter VAG 1274/9shown in diagram (or equivalent).
Install hand pump and build up pressure.
Pressure relief valve should open at 1.4 to 1.6 bar.
Replace filler cap if necessary.

DO NOT replace coolant reservoir if there is no further coolant leak detected around the coolant reservoir.