audiohs

I installed a boost gauge over the weekend and noticed that the car runs in vacuum state most of the time except for when you're on the gas. This is also confirmed at Seans A4 page. So does that mean the turbo is not spooling? If it does, then is the cool down really that necessary if the car is running in a vacuum state most of the time? I have been religiously idling the car for one minute before I turn the car off. I had always thought this was to let the turbo to spool down. Plus, I usually take it really easy just before I park the car. I can see the benefit of letting the car cool down after a spirited run but I'm wondering now if the one minute cool down is really necessary. Maybe I'm doing more harm by letting it idle each time? Maybe I should shorten the cool down cycle? Any thoughts?

BlueMaxx

keep oil circulating through the turbo as it cools down so oil doesn't sit and fry (itself and the turbo).

Andy_FL

You're right...the majority of the time (depending on your driving style of course), your car runs at vacuum. In other words, you're not using the turbo. However, I'm not sure that you can assume a shorter idle-down time just because the turbo was spooled up maybe a total of a minute over a 30 min timespan. You've still got hot oil circulating through the turbo because it's connected to the entire oil system, of course. So unless you've gone on a really really short drive (ie...oil temp stays low), you're best off idling down for at least a minute EVERY TIME. hope this clears things up....

Andy

Hokie_Audi

Your engine spends most of the time pulling a vacuum on the intake side, as you confirmed with the boost gauge. Though it's important to note that whenever the engine is running, particularly when you're at speed, say around 2-3 thousand RPM, a large volume of exhaust gas is passing through the turbo, all the time. This gas is hot, around 1400 F and it all has to pass through the turbo first.

Even when you're not "on the boost" your turbo's bearings are still working. Turbo's spin at incredibly high rates even when there is no noticeable boost effect.