Modifying the Afterrun Pump control on S4/RS4

[Thorney]

I always run my car for a little while after using it hard anyway.

[Joules]

Maybe, but then you'd have to remove ECU control of it. So if there really was a problem where the coolant got too hot, then the ECU wouldn't run it for up to 10 minutes.

But you could wire it in parallel so the ECU could still function??

To be honest I too leave the car to stand after a blast

Joules

[RobK]

The after-run pump still doesn't circulate oil though. As I understand it the primary risk is that the hot oil could leave a residue (do synthetic oils coke?) on the inside of the piping which restricts the oil flow. And when a turbo is starved of oil it tends to go bang. This was seen as a likely cause of many of the S4 turbo failures.

[Dippy]

But you could wire it in parallel so the ECU could still function??

That depends on what sort of drive it is, I haven't looked. The main issue is what happens if you apply 12V to an ECU output when it's off. If it's connected to earth then you'll have a short which will cause damage, and this might me in the ECU itself, and there could be consequential damage to other parts of the ECU etc etc.

Whenever you modify a system, the golden rule is to do it the easiest way which will cause least interference to the system. Using a VFC to 'mimic' the sensor obeys this rule the best.

Cheers,
Dave

[Dippy]

The after-run pump still doesn't circulate oil though. As I understand it the primary risk is that the hot oil could leave a residue (do synthetic oils coke?) on the inside of the piping which restricts the oil flow. And when a turbo is starved of oil it tends to go bang. This was seen as a likely cause of many of the S4 turbo failures.

Yes Rob, that's true. However for an oil to leave such a deposit (and yes synthetics can coke, all be it less than mineral oils), it needs to reach a high temperature for a while. Ideally I'd have the oil circulating too, however simply by cooling the turbos as quickly as possible by circulating the coolant for a couple of minutes should do the job.

Don't forget that by idling the engine you are heat-soaking the engine bay. Yes the oil cools, but the turbos won't cool anyway near as much as by using the afterrun pump. So when you do eventually turn off the engine, there is still the risk of hotspots in the turbos.

Also, how many of you REALLY idle the engine for LONG ENOUGH, EVERY TIME?

[Thorney]

The cooling effect of circulating oil round the turbos more than outweighs the heat soak effect.

And yes, if the car is run hard I left it run religeously to ensure the turbos have time to cool down.

[Dippy]

OK - I'm not trying to sell this idea to you guys. Don't forget that the afterrun pump was Audi's idea not mine!

I just posted this for info for anyone who is interested. For me it was certainly worth the effort as sitting in the car for minutes after a hard run was starting to irritate me. If you don't mind doing it then clearly this mod is not for you.