Joe Weinstein

Experts like Stephen Kaspar (PorschePHD) have taken turbo temperature measurements,
and they show the turbo gets significantly cooler idling than it does with even the most
gentle slow driving, so the cooldown idle period is always beneficial.
Joe

twinsnail

I wonder why the manual for the 996 tt minimizes this; something like idling for about a minute after hard driving, I'm not sure but I don't think they recommend it at after every drive I remember that my friends with Saab turbos were keen on this

Dock

According to Porsche, the turbos rotate at ~10,000 rpm with the engine at idle. I may not understand the system well enough, but that tells me that the rpm of the turbos is tied to engine rpm and not to "boost".

I idle my Turbo for ~2 min every time I drive it to allow the turbos to spin down towards 10,000 rpm.

tkerrmd

+1

ltc

You don't have to understand the system that well. Think of a water wheel.

Turbo = gas driven blades on a disk (paddles on a wheel)
RPM's are proportional to exhaust gas/fuel burned, as is EGT (exhaust gas temperature)
So, as RPM's go up, the turbo has to spin faster....as RPM's go up, so does exhaust gas temperture, hence turbo blade temperature.

1AS

I don't cool down at all, for any street driving. I don't have the time or patience, and at 38,000 miles, it doesn't seem to have mattered. In the few times I've tracked this car, I have let it cool down.
The manual doesn't advise it for daily driving, and I feel it is too much of an inconvienience for a daily driver. Plus, I can't sit an do nothing for 2 minutes. AS

wross996tt

Note to self...do not buy AS's car if it goes for sale.

Dock

I understand the physics. I was just pointing out that just because the car is driven without any indicated boost does not mean the turbos aren't spinning at high rpm's. Cool down is not done because there had been boost, it's done because there has been rpm on the engine (spinning the turbos) - turbos spinning at high rpm (higher then 10,000 rpm) don't need their oil supply removed.

Kevin

Alexander I'd love to have your turbochargers as my poster child..

Promise me that when they start to puke oil, you'll give me the call

porschedude996TT

FYI,

I don't know what Max RPM our Automotive Turbos turn, but my aircraft experience tells me somewhere between 60,000 and 100,000 RPM.

Fred R. C4S

Same speeds for big yellow diesels. Our cool down can be up to 5 minutes or longer. Despite having water cooled center bearings, we are trying to radiate heat as well as allow the turbines to slow down. Heat is the killer, not the speed.

Cheers,

FixedWing

The first time I flew in a turbocharged airplane I was impressed with just how long you had to idle even after a long taxi before the turbos cooled enough where you could shut down.

On the Turbo, my feeling is that primarily you want to give the turbos time to spin down as much as possible and that secondarily you want to cool them down before shut down. So I will always idle the car for at least 30 seconds no matter what and then I will extend that depending on how I have been driving.

As for PAG minimizing this issue, I think that they resolved the big warranty problems with their oil reservoir. That allows the turbo to remain oiled while shutting down. Heat issues are not going to affect the turbos for some time. And I don't know about everyone else here, but my impression is that the turbos in our car are very reliable.

Stephen

Dock

Our turbos run ~150,000 rpm at full boost, and the maximum designed rpm is 170,000.

1AS

Kevin,
If they go, you can have them. My point in posting is to share whatever I learn with others who ask the question. Pierre, who occasionally posts here. put about 120,000 miles of hard use on his engine. While he did replace it, the turbo's had not failed.
I think I'm nearing the point where you had predicted failure in an earlier thread. Time will tell. AS

jcb-memphis

I have moved to 60s for simple driving and 120s for anything with boost in the last 5 minutes, even 0.1bar. Just what I am doing. If I tracked, I probably would go 4-5minutes/a lap too, but I don't.

If the turbos did not fail, people like Kevin would have a lot less business. They fail. I have seen Audi's go up, Saabs, one 930's.....so in time with abuse, these will too. It is probably a bell curve...some peoples' will fail with good care and others will never fail with abuse. I suspect Porsche knows....

Just my opinion. I just listen to music.


JB