the turbo timer allows the car to idle after the ignition is turned off and the key is pulled -- this keeps oil circulating to the turbo, cooling it and keeping it lubed.

this is especially important because, coming off any sort of a speed run, the turbo can be literally red hot. If the car is shut off then the oil in the turbo at that time can cook - more literally coke. turn to sticky tar and ultimately plug the oil feed line and lubricating journals in the turbo. no oil, no lubrication.

[I've heard that this is a greater problem w/ conventional oil, which can coke. synthetic oil may burn to ash, which is more easily flushed out the next time the car is started. either way, not so good for the tubo.]

You can use a turbo timer to enforce this cool-down or you can be a bit aware and do-it-yourself: When I autocross, I'll let the car cool for 3 - 5 minutes before shutting it off.

If I drive home, my ride is on dirt/gravel, enforcing an easy pace for the last few minutes of that drive -- I don't need to cool it down at all ariving at home.

But if I just arrived someplace after a brisk (fast, on-boost ...!) drive then I'd want to sit for a few minutes before shutting it down.

on the other hand, if that drive culminated in 15 minutes of off boost stop/go driving I wouldn't bother. A good synthetic oil is your best protection.

ymmv.

 

They're pretty much completely unnecessary on any water cooled turbo. On older oil only turbos once the engine was turned off the oil stopped flowing and cook in the turbo. If you've been running it really hard it's still a good idea to let the car idle a little bit or drive lightly before you stop.

 

They're pretty much completely unnecessary on any water cooled turbo. On older oil only turbos once the engine was turned off the oil stopped flowing and cook in the turbo.

Turbocharged Subaru engines also benefit from a nifty little design trick. The coolant header tank is located up on top of the inlet manifold with good reason - it provides for some minor circulation of coolant through the turbo by way of a 'thermal siphon' effect.

 

http://www.scoobymods.com/forums/showthread.php?t=2388

 

All Turbo water cooling after switch off is by thermal syphoning...and all header tanks are high up, not sure its a nifty Subaru thing!

On Ford Escort RS turbo's in the UK (turbo at the front of the engine bay) some after market tuner (can't remember which one) showed a turbo out temperature benefit by passing the coolant through a small cooler prior to it going through the turbo, not sure thats practical on a Subaru though given the turbo's location!

Timers not necesary on a water cooled turbo unless you drive like a total idiot and then switch off straight away, even then a good synthetic oil will give more benefit for less money than a TT.

Simon

 

All Turbo water cooling after switch off is by thermal syphoning...and all header tanks are high up, not sure its a nifty Subaru thing!

Interesting! I've never really noticed it on other cars before (most seem to have the standard radiator fill point with no header tanks located close to the turbo). I'm probably not looking carefully enough though!

 

Is the stock XT turbo oil or water cooled?

 

Water cooled.

 

In all honesty if you've been driving very hard you really should drive slowly an extra mile or so before you reach your destination because all the other bits like brakes, coolant and oil would benefit from a cool down lap a lot more than the turbo. If your brakes are super hot you don't want to stop and have the pads sitting in one spot while it cools down.

 

I have one and it's set for 20 seconds. I hit the button to shut it right off prolly half the time from driving casually. I simply wanted to leave the vehicle running while locked. When I first moved 1,000 miles away (to CO) I moved into apartments. With my job I kept nearly $1,000 dollars worth of tools/equipment in my Forester. I needed it locked. PLus I like the vehicle warmed up and safe to drive. I hate how slow t takes to warm up our 4 cyl. in the winter. I litterally was at my boss' house when I was at operating temperature. Honestly tho I wouldn't have gotten one unless it had the boost feature like my Blitz. It's a nice lo-pro way to have a boost gauge.