Background
There was a 2019 recall on all Gen 1 2007-2015 Audi R8 vehicles due to the coolant expansion tank failing, resulting in engine compartment fires. The coolant tank is located directly above the exhaust manifold and when the tank fails, coolant is dumped on the exhaust manifold. Because modern coolant is highly combustible at high temperatures, it instantly causes a fire in the engine compartment. The recall resolution is to install a metal tension band around the coolant expansion tank to reduce the severity of the failure by minimizing the rate at which coolant escapes when the tank ruptures at the seam. With the metal band in place, only a small amount of coolant “steams” out, resulting in the rear glass fogging up, but eliminating the chance of an engine fire. The recall does not, however, solve the underlying problem causing the tank to fail in the first place. The tanks will continue to fail every few years.
Cause of Coolant Expansion Tank Failure
The coolant expansion tank fails because the coolant being sent to the tank is too hot, exceeding temperatures of well over 150 degrees C. This exceeds the thermal fatigue temperature of the expansion tank, meaning that it will progressively weaken with each over-temperature event. Over time, these over-temperature events will cause the tank to fail at the plastic welded seam around the perimeter of the tank. The metal band doesn’t prevent this failure from occurring; it only minimizes the severity of the failure when it does.
Resolution of the Problem
To completely address the underlying problem, it is necessary to lower the temperature of the coolant sent to the overflow tank. This prevents the expansion tank from becoming too hot and failing. This temperature reduction is accomplished by moving the expansion tank feed point from before the radiators (where coolant temperature is highest) to after the radiators (where coolant temperature is lowest.) This is accomplished by connecting the coolant expansion tank pick-up line to the coolant fill vent point at the outlets of the front center radiator. The original pickup points (before the two side radiators) are then converted to coolant fill vent ports. When performing a coolant fill after the conversion, the coolant is vented at two points (near where the coolant enters each of the side radiators), rather than at one central point (immediately after the front center radiator.) A full discussion of the root cause diagnosis, including commentary from an Audi engineer on the R8 team, is available here.
The coolant expansion tank should be replaced with a new tank when this rerouting is performed because the old tank has likely experienced multiple over-temperature conditions and is partially fatigued.
Instructions for Coolant Line Rerouting:
Note: all of the coolant lines being modified are at the front of the car. The front trunk insert must be removed to access these hoses. Instructions here: https://www.r8talk.com/threads/replacing-battery-how-to-remove-trunk.12485/
Parts Needed:
- 1x angled vent tube (420-121-060-A)
- 1x Straight Coolant Line Coupler (###-###-###) (pictured below)
- Disconnect angled Dark Blue Angled Vent Tube 17 from Dark Red Connector 16 (shown in diagram below)
- Save this hose – it will be reused in Step 2
- Leave this port on Connector 16 disconnected for now. It will be reconnected in Step 3.
- Remove Yellow Hose 22 and block-off the open connections at both ends.
- Disconnect Yellow Hose 22 at both ends. Yellow Hose 22 is not needed and can be removed and discarded.
- Install Dark Blue Angled Vent Tube 17 (removed in step 1) to the small connector of Orange Fitting 11 (where Yellow Hose 22 attached to Fitting 11.)
- Remove the Green Y-connector that was at the right end of Yellow Hose 22 and install a Straight Connector (part number ###-###-###) so that Red Hose 23 connects directly to Purple Hose 54
- Re-Route Inlet Flow for Red Hose 23.
- Disconnect the right end of Red Hose 23 from Pink Fitting 6
- Install the additional Angled Vent Tube 17 (part number 420-121-060-A) to the small connector of Pink Fitting 6
- Connect the right end of Red Hose 23 to the small connector of Dark Red Connector 16 (this is the port that was left open in Step 1)
Replacing the Coolant Expansion Tank:
Now that the hot coolant flow to the expansion tank supply has been eliminated, the coolant expansion tank should be replaced with a new tank that has not experienced any thermal fatigue. The mental band should still be installed on the replacement tank as a precautionary measure.
Part Numbers:
- Original R8 coolant tank: 420-121-403
- Audi Q7 Part Number: 7L0-121-407-F (completely identical to the R8 tank but it costs substantially less)
- Expansion Tank Tensioning Strap: 420-121-263 (can reuse strap from old tank – if available)
- Tensioning Strap Bolt N-010-287-12 (can reuse bolt from old tank – if available)
Make sure you install the metal band around the seam of the new coolant expansion tank. Transfer it from the old tank or order the parts. Better safe than sorry!
Video Instructions for Installing a new Coolant Overflow Tank: