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Oil and Octane recommendations
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skytrooper  



Joined: 29 Aug 2007
Posts: 461
Location: Canandaigua, NY

PostPosted: Tue Jul 22, 2008 4:28 am    Post subject: Oil and Octane recommendations Reply with quote

'81 931 approximately 77k miles. What octane fuel is rocommended and what oil should it have ?
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Matt

1987 - 924S "Black Pearl"
1982 - BMW 633CSi
1984 - BMW 528e
1983 - 944 N/A "Blue Max" (Gone)
1981 - 931 "Scarlet Harlot" (Gone)
1976 911S Targa (Gone)
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11724
Location: PacNW

PostPosted: Tue Jul 22, 2008 4:40 am    Post subject: Reply with quote

I think the manual calls for regular 87 gas at stock US boost levels. As for oil, I just took Shaggy off of 20w50 Mobil1 and switched him to 10w30. This was done at the suggestion of a mechanic buddy of mine, who explained that because synth is slipperier than dino oil, it doesn't need as much viscosity. The benefits are more power and better mileage. . .so far both have panned out exactly as he predicted. As a bonus, the turbo seals seem to be blowing less oil into the intake. The car is running great, and oil pressures are within FSM spec.

I'm sure there won't be much agreement on this one, but. . .
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  • WeiBe (1987 924S 2.5t) - 931 S3
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Tue Jul 22, 2008 5:28 am    Post subject: Reply with quote

The advantage of synth is that it deals with heat better than dino oil - which I think is reason enough to use it in a turbo. Especially in a turbo that is known for oil coking in the bearing housing. In cold climates, synth doesn't get as thick at very low temps. This greatly reduces general engine wear. I always go as thin as possible with oil - less resistance.

For octane, you might consider 89 (US) on a stock US car - even if the manual calls for 87. Only because of all the additives in fuel now. You definitely want 92+ if you turn up to the RoW boost of 10psi.
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet
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cgalyon  



Joined: 05 May 2008
Posts: 249
Location: Knoxville, TN

PostPosted: Tue Jul 22, 2008 5:56 am    Post subject: Reply with quote

I use a 924S instead of a 931, so there are obviously engine differences, but I use 92 octane. I believe the manual calls for 89 or something, but my engine really runs much more smoothly and powefully with the higher octane.

As for oils, I have another question: what are the drawbacks to synth (other than cost)? Is there really any reason to stick with regular oil over synth when cost isn't considered a factor? I think I might see about switching my car over to 10w30 synth too if there's no reason not to.
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tuurbo  



Joined: 08 Aug 2007
Posts: 1446
Location: East Windsor, New Jersey

PostPosted: Tue Jul 22, 2008 6:03 am    Post subject: Reply with quote

I use the highest octane I can get and I use methanol and water to control detonation just in case. 10 PSI, slightly advanced timing.

I've used 10/30 in winter but use 20/50 in summer.

Sooo a 10W30 is ok in hot weather?
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1980 924 turbo, MSD, Meth. Inj, otherwise stock.
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11724
Location: PacNW

PostPosted: Tue Jul 22, 2008 6:46 am    Post subject: Reply with quote

cgalyon wrote:
Is there really any reason to stick with regular oil over synth when cost isn't considered a factor?


Someone will correct this if I am wrong, but I synth may have a higher level of detergents than dino oil. If you have a high mileage motor, this can cleanse away engine goo from old seals and cause them to leak.
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  • WeiBe (1987 924S 2.5t) - 931 S3
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Smoothie  



Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)

PostPosted: Tue Jul 22, 2008 8:34 am    Post subject: Reply with quote

Meah, I'm pretty sure that one's a myth. Amsoil mentions it under #1 here - http://www.synthetic-oil-tech.com/d.cgi/1183153/ten_myths_about_synthetic_lubrication.htm
From personal experience, what they're saying is true. I switched to synthetic (Mobil 1) in 1996 and had no leaks before or after switching.

Your main reason for using synthetic in a turbo engine should be to reduce coking in the turbo to extend its' life. -But there are other benefits such as extended oil change intervals, which btw result in either savings or costing about the same as a conventional oil. -So the main benefit for a 924S owner might be reduced cost and fewer oil changes. I go for about a year between synth oil changes, but obviously it's mileage dependent, so if you do a lot more, like 20k-30k per year you'd be looking at 2 or 3 oil changes in that time, depending on the oil (some synth oil recommended change intervals are about 6k or 9k miles, others 15k or more).
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'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11724
Location: PacNW

PostPosted: Tue Jul 22, 2008 10:05 am    Post subject: Reply with quote

Oh yeah, and FWIW I switched my 2.5 to synth at 120k miles and it doesn't leak or burn a drop.
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flosho  



Joined: 01 Jul 2004
Posts: 3156
Location: Eau Claire, Wisconsin

PostPosted: Tue Jul 22, 2008 11:20 am    Post subject: Reply with quote

I run 20w50, because I believe it holds up better to pounding on the car, doesn't leak but a few drops after hard driving, and thats because I re-used the same washers on the oil lines going from the turbo drain, and on the oil filter adapter.
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cgalyon  



Joined: 05 May 2008
Posts: 249
Location: Knoxville, TN

PostPosted: Tue Jul 22, 2008 10:37 pm    Post subject: Reply with quote

My engine has about 180k on it (by PO report since the odometer doesn't work anymore and apparently hasn't for a loooong time), so I probably ought to do whatever is best for a high mileage engine. I don't know a whole lot about the effects of the different viscosity levels for oils, but would there be any harm in trying 10w30 and if that doesn't work well (begins leaking for example) drain it and switch back over to 20w50?
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ideola  



Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI

PostPosted: Wed Jul 23, 2008 12:44 am    Post subject: Reply with quote

I run 10W40 synth in the winter and 20W50 synth in the summer. I change the oil in my cars twice a year, even though they are all driven well below the mileage. I've not had a single problem on ANY of my cars running synth. I can't attest to the mileage or power differences between 10W30 and the heavier oils because I haven't done a direct comparison. The higher oil change intervals for synth results in lower total cost for annual maintenance. If you go 15K intervals, it's nearly half the cost (if you include a new filter with every change).

As for octane, I've run 87, 89, and 92+ in the NA, the 924S as well as my SI 931 running stock boost. I've not noticed one bit of difference between the running of any of the cars, so now I just run 87. I have a chip for the 924S that I haven't installed because it requires running premium, and with the cost of fuel these days, and considering it's my sons daily driver at the moment, it doesn't make sense. I've always run 87 in the 928.
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cgalyon  



Joined: 05 May 2008
Posts: 249
Location: Knoxville, TN

PostPosted: Wed Jul 23, 2008 5:56 am    Post subject: Reply with quote

That I appear to get a significant performance difference with higher octane could be a sign of the need to clean out my car's fuel system (or perhaps a sign of some crap they're putting in the gas around here). The easiest way to describe it is that my car simply seems "happier" running on higher octane. I used to balk at the notion of paying an additional $0.20 per gallon for the higher octane, but that works out to about +$2.00 / 10 gallons and I run through about 7.5 gallons per week. So in an entire month that amounts to ~+$6.00 or about +$72.00 / year. It's a fairly nominal amount overall and appears to help it run better.

What's the mileage on your cars, Dan? I wonder if the difference could be attributable to the mileage on it. If not, then I have no idea and without objective measures, it's all just anecdotal evidence.
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alexvex  



Joined: 31 Jul 2006
Posts: 420
Location: Seattle, WA (from Indiana)

PostPosted: Wed Jul 23, 2008 6:29 am    Post subject: Reply with quote

I switched over to Mobil1 in my Audi from the PO putting jiffylube whatever oil in it. Car has 235k, hasn't smoked a drop of oil...before or after the switch to synth.
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--Alex--
1992 Porsche 968 (VW 2.5L I5 Turbo swap in the works)
1995 Audi 90 Quattro Sport (4.2L V8 Swap)
2010 Touareg TDI
Past Pcars: 80 931, 87 924S, 87 951
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ideola  



Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI

PostPosted: Wed Jul 23, 2008 12:44 pm    Post subject: Reply with quote

I haven't measured MPG in any of my cars recently. The 924S at last recollection was getting about 25 MPG. The NA seems to be doing very well on two recent 100+ mile trips (mostly two lane highway)...the last trip, I went thru less than half a tank and did ~190 miles.
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flosho  



Joined: 01 Jul 2004
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Location: Eau Claire, Wisconsin

PostPosted: Wed Jul 23, 2008 12:58 pm    Post subject: Reply with quote

Also, I only run 92 or 93 octane in the 931 regardless of when it was CIS or EFIed now.
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