question about turbos
 

this is my first car with a turbo so i have question. my friend has a 240 that's jap-spec so it has the turbo and all the other fun stuff they took out when they imported them and everytime we go anywhere he lets the engine idle for like a minute after parking before he turns it off. I never really paid attention to it before but the explanation was "something, something something, something, turbo something" (at least that's what I heared) but after getting my s70 i noticed in the manual it says not to "race" the engine right away after turning it on. is there something to this? should i idle it a bit before turning it off and let it "warm up" before i get on the freeway?
i'm sure his car is running at higer pressures and such so i'm not to worried about it but i am courious...

thanks!

From what I understand, the turbo can be damaged if it is stressed prior to warming up. Also, it's good to let it cool down before you cut it off. If you are racing home, and cut the engine off, the turbo will likely be very hot and can be damaged if not cooled down properly.

I believe oil runs through it. When you let the motor warm up before you fire cool oil through a turbo that is heating up fast it will last longer. Also you should let oil cool down a hot turbo before you park and shut it off. I believe you should let your engine reach it's operating temp before kicking in the turbo and alway drive your last 2 miles or so or let it idle for a couple of minutes before you turn the car off.

+1 to the above post.

Your S70 will have a mitsubishi turbo. might be a 16T...
It is a journal bearing type turbine, which I believe the shaft floats in a thin film of oil for lubrication.
This is why they say to have a cool down time and time to let the oil reach operating temp, And I believe the oil takes longer to heat up.

What is nice is the Mitsubishi turbos are water cooled, which typically have a better chance of not being damaged when your average person abuses this "rule".

Side NOte: The ball bearing turbo are more prone to failer if the drive abuses the "rule" for the oil lubricates the bearings and if you are aware, the turbine will keep spining even after the car is shut off after being reved.

The older non liquid cooled turbos were VERY sensitive to being shut down hot as the engine oil was the only thing that cooled the centre section. If teh turbo was really hot on a shutdown, you could coke it up right there and then.
All turbos run on a "wedge" of pressurised engine oil, so, giving teh engine a big rev before shut down allows the turbo to spin on with no lube. Revving hard on start up does a similar thing.
The only really bad thing not letting a modern water cooled turbo does is allow slow coking of the bearing and oil passages, it's a long, slow process, one really hot shutdown won;'t do it.
But, every day driving, say a sedate commute to work, you really don't need to idle down the turbo, it won't hurt, but not necessary.
You'll do far more damage missing an oil change than you will a few hot shutdowns.

Regards, Andrew.

On start up, oil needs to flow a few seconds before it reaches everywhere its supposed to go with operating pressure. That's why the start up idle rule. On shut down, you need to allow cooler oil to flow into the turbo's bearings to cool the hot turbo. That's why that rule. If the superheated turbo is shut off, the oil cooks (cokes) and gets solid particles over time. That's a reason you don't see old Chrysler turbos on the road, or those TBirds with the 4 cylinder turbo engines.

Rule of thumb: idle 15 to 30 seconds each way (depending on start up temp and shut down's immediately prior use of engine) and you should avoid trouble. Also, this is why people like full synthetic oil in turbocharged vehicles since synthetic oil flows easier and is more resistant to heat coking. Also, a lighter foot on the gas engages the turbo less, meaning longer life so it will be there when you need/want it.

Owner's manual for '06 gives these cautions about don't race the engine before shut down.

awesome! thanks for the info everyone!

The turbo is always spinning when the engine is running, a "lighter foot" doesn't do a thing for turbo life. It doesn't come on or turn off at certain speeds, it is a load driven turbine. More gas volume equals more flow, equals more compressor and turbine speed. Even at idle a turbocharger is spinning.
Of course, I can point to marine and continuous duty diesel engines as an example of constant boost for thousands of hours, but internetz knowledge is bettah.

Regards, Andrew.

But at higher rpm, at least until the limit is reached, you're putting more hot exhaust gas through the turbo and therefore more heat. I realize that turbos are always spinning, but the pressure and heat increases with increased rpms.

They cool at lower rpms, thus the utility of a cool down idle after running, especially after a hard, higher rpm, run.

Sounds like we are splitting hairs a little so I'll chime in. I watch my boost guage a little and see that it's more of a load thing that triggers the boost than it is a rpm deal. I can be cruising about 75 mph with the tack near 3,000 rpm's and the boost guage will be pretty low. But when I'm picking up speed from say 25 mph to 60 mph and I have a load on the engine, even though I may not be reving that high, between 2k & 3k, I'll notice that I will be in boost a little.

That leaves me with a question... People alway refer to the turbo's action as "spooling up", does that mean it is spinning faster? When I am in boost, is it turning faster than it does when I'm just cruising at 3,200 rpms? Does the turbo turn slower when it's at 25% of my guage indicator than it does when it's at 50% of my guage?

that does make me wonder... has anyone ran a turbo with an RPM meter in the turbo itself to see exactly whats goin on with it?

I don't think that is possible. Just a boost guage.