Turbo residual heat question.

[sscates]

I know that heat is a turbo's worst enemy. How long does a turbo need to cool down after a short boost period of say, 15sec? Just curious, there is an uphill section about one mile from my house that I like to run on. Just curious if it is doing any damage to shut down 2-3 mins. after. Mine is original equipement 82' 930.

[Emission]

Depending on how hard you are pushing it... a 2-3 minute idle should be fine to cool down the turbo. Now, understand, that is just cooling down the oil-cooled turbo bearings to hot oil temps, not everything else (wastegate, turbo housing, exhaust, etc...). If you really want everything "cooled down" you'll need to drive without boost for the last five minutes or so (painful, I know).

I run mine pretty hard, and I will idle a few minutes in my driveway (and leave the lid open after I park to get rid of some of that residual heat). I also use synthetic oil.

[cowtown]

Emission, what viscosity synthetic are you using here in CA for your 930?
Thanks,
Colin

[Emission]

Mobil 1 15W-50

For turbo engines, it offers that extra margin of safety as it is excellent in high-heat situations.

[sscates]

Emission, thanks for the input. Did you switch to Mobil 1 or did your car come from the factory with it? I've heard that switching mid-stream causes leaks. As if our cars don't have enough leaks. I run Castrol 20-50. One more question, how far above the white line does your oil temp get in the summer time? Thanks again.
Nice collection of cars!

[Emission]

Originally posted by sscates
Emission, thanks for the input. Did you switch to Mobil 1 or did your car come from the factory with it? I've heard that switching mid-stream causes leaks. As if our cars don't have enough leaks. I run Castrol 20-50. One more question, how far above the white line does your oil temp get in the summer time? Thanks again.
Nice collection of cars!

The previous owner used regular oil at 3500 mile intervals. The car did not leak one drop.

When I bought the car (at 118,000 miles) I switched to annual synthetic changes (about every 4000 miles). The car now leaks.

Synthetic oil has detergents that break down deposits and build up (the crud that plugs leaks). It doesn't "make" leaks, it exposes them. To me, the advantages of synthetic with a turbo outweigh the cons of a few drips of oil.

I just put a numeric oil temp gauge in this evening (what timing!). It used to run about horizontal (9 pm), until I put in an oil cooler scoop and made a dam to keep air from spilling out under the oil cooler. Now, it is much cooler (8 pm on the dial).

Thanks!

[dean]

You should not have a problem with the hill. Just don't go into boost. I think people tend to worry about this too much. I have had turbo vehicles for a long time. I have never let them idle before shut down. I don't go into boost for a min. or so before shut down. I have never had a turbo failure

[sammyg2]

If you are really concerned you can get an electric timer that shuts down the engine after a pre-determined time.
You basically pull up, turn off the key and get out of the car (making sure you lock it). After 5 minutes or whatever you have it programmed to, the time shuts the engine off.
I figure it's overkill but they are out there.

[Emission]

Originally posted by sammyg2
If you are really concerned you can get an electric timer that shuts down the engine after a pre-determined time.
I figure it's overkill but they are out there.

I agree it is overkill. Some of those more advanced "Turbo Timers" also control the boost and have accurate boost gauges too.

[afterburn 549]

you could always install a egt guage and then you would know.

[Steve W]

I'd still vote for idling at least 2 minutes prior to shut down. 15 seconds at full boost is what I would consider a hard run. The heat from the turbine is just so much that will heat soak to the center bearing section and potentially cause coking of the motor oil, eventually leading to seal failure.

[Emission]

Originally posted by Steve W
I'd still vote for idling at least 2 minutes prior to shut down. 15 seconds at full boost is what I would consider a hard run. The heat from the turbine is just so much that will heat soak to the center bearing section and potentially cause coking of the motor oil, eventually leading to seal failure.

I have to agree. It is rare to run even more than 10 seconds on full boost. Most of the time it is boost for about 5 seconds (as the engine climbs from 3000 - 6900) the off boost for a second or two then back on for another 5 seconds...

I have run "full boost" only on long straights on the track (even then, only about 5-10 seconds), or when I am on the highway in 3rd or 4th and really open her up.

[sscates]

You guys are probably right. Closer to 5-10 sec on boost. I like the idea of the EGT guage. I believe that takes the place of the clock and looks factory. Anyway, it's hard to believe the turbo seals haven't went out on an original 82'. Emission, that is pretty high miles from what I've read about turbos. If you don't mind me asking, what kind of problems have you encountered? Mine has 46k, with regular mx and a new clutch in 2000. I've had it for about six months and am amazed at the durability of the car. I've done some small mx items, 4 wheel alignment, brake lines, test pipe (don't know if I like it or not), tires (S-03's). Thanks.

[Emission]

Originally posted by sscates
Emission, that is pretty high miles from what I've read about turbos. If you don't mind me asking, what kind of problems have you encountered?

I got mine in April 2002 with 119,000 miles on it. Now, it has 129,000 miles on it.

The turbo was replaced at 111,000 miles for the first time (that is pretty good and indicates the PO took care of it). The clutch was done at 113,000.

I've had 18 months/10,000 miles of nearly trouble-free driving. I did replace all the hoses and belts (myself), and my wastegate O-rings needed to be replaced (DIY too), but everything else was just Porsche maintenance.

Oh, I did reduce the boost from 1 bar back to stock (.8 or so) to put less stress on the engine as it was predetonating with the hot weather and lousy high-octane gas. The PO put a K27 in when he replaced the turbo and a 1 bar spring. I may go back to 1 bar when I can run some better fuel (we only get 91 out here in CA).