When I owned my '91, I routinely changed from 10w30 in winter to 15w50 in summer and had no problems. I live in Louisiana and 15w50 is NOT too high a viscosity for this climate in summer, but I wouldn't run it in winter, even here. The oil has a higher viscosity and it isn't surprising that it would seem smoother and quieter, but it may also marginally affect your mileage (downward). Since it is thicker when cold, it may take marginally longer for it to reach vital components, which isn't a good thing--but some synthetic oils, M1 being one, tend to cling to metal surfaces when not running, which mitigates this phenomenon somewhat.

This will shock some here, but this is a quote from the Saab service manual (0:2 Technical Data, p. 022-19):

"Visocity: SAE 10w30 or 10w40. In markets where these viscosities are unobtrainable, 15w40 may be used instead. Use 5w30 or 5w40 in climates with temperatures consistently below -20°C (-4°F). These oils should be of all-synthetic or semi-synthetic type. At constant temperatures of +15°C (+59°F) or above, use 15w50 or 20w50."

The 59°F spec will be met in most areas of the U.S. in summer.

I have run another brand of synthetic for the past six or seven years, a 15w40, year 'round rather than switching seasonally. Lab tests tell me I'm on the right track.

• oil changed from 10W30 to 15W50, quattro, Tue, 8 May 2001 13:47:54
  • AH, THE ANNUAL OIL SLUG-FEST., Robert Kaplan, Thu, 10 May 2001 10:29:59
    • Re: AH, THE ANNUAL OIL SLUG-FEST., Dick in Falls Church, Thu, 10 May 2001 20:53:03
  • Re: oil changed from 10W30 to 15W50, Dick in Falls Church, Wed, 9 May 2001 10:43:50
    • Re: 10W40 or 15W50 is a better choice in summer, Sjer, Wed, 9 May 2001 16:52:09
      • Re: 10W40 or 15W50 is a better choice in summer, Dick in Falls Church, Wed, 9 May 2001 22:37:47
    • Dick, I think you're dead wrong..., Robert Davis, Wed, 9 May 2001 15:32:48
      • Re: Dick, I think you're dead wrong..., Dick in Falls Church, Wed, 9 May 2001 22:44:09
        • Re: Dick, I think you're dead wrong..., Robert Davis, Thu, 10 May 2001 09:55:52
  • Okay guys, be ready for a shock, Robert Davis, Wed, 9 May 2001 01:38:42 <-- Viewing This Message
  • Why does Saab recommend 10W30?, Gepost, Tue, 8 May 2001 21:14:23
    • I so agree..., VIKINGMAN, Wed, 9 May 2001 10:02:39
  • Had the same exp., David L, Tue, 8 May 2001 13:53:55
    • Re: Had the same exp., quattro, Tue, 8 May 2001 14:21:32
    • Re: Had the same exp., quattro, Tue, 8 May 2001 14:08:27

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