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, Sat, 17 Feb 2001 13:57:08
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>> Down in Miami florida and two diffenet local indies recommend and
>> change with 20w50. They both say between the stop and go pure city
>> traffic and the heat the 10w30/40 just breaks down too fast and doesn't >> protect as well or enough. Between 10w30 and 20w50 I haven't noticed a >> change in my gas mileage.
I disagree with this assessment. Any modern synthetic in an appropriate viscosity range will not break down significantly in city traffic. I've used 15w40 RP for a number of years in my present and previous 9K, and recently lab tested it after 5k and 10k. At 10k the oil had lost little of its viscosity, showed very low wear metal content, oxidation was low, and TSB at a safe level. We have weather similar to FL here in Louisiana, but probably colder in winter. I really can't imagine an area of this country that would benefit from a 20w50 in a Saab. I use it in my Harley, but that's an entirely different environment, though oil temps are actually lower there than in most Saabs (never higher than 180°F).
If non-synthetic is used, I would agree more with your indies. Fossil oil will oxidize much more rapidly under extreme heat. But with the oil cooler present in all Saab turbos, it is unlikely temps will be elevated beyond a safe level, even though passage over the cooler will slow in slow traffic. The thermostat for my Aero is 225°F, and I've never seen it climb above 220° in any conditions, even stop-and-go traffic in summer. This is not sufficient to bother even fossil oil significantly, though if used it should be changed at least every 3k regardless. Older 9K's have lower oil-cooler thermostat specs, my '91 being 194°F. It never got above about 180°F using RP, though the Mobil 1 I used before it ran about 10°F higher at max. Temps were observed by a VDO oil temp gauge, measured at the drain plug--but will obviously climb higher in certain parts of the engine.
Thicker oil flows slower when cold, and immediate flow to engine parts is critical when first started after prolonged idleness, like overnight. Most engine wear is achieved when first started, so a thinner oil protecting at that instant may be more important than a thicker oil protecting for the duration of a car's operation once running.
I doubt if a ?w50 oil will harm a Saab in hot summer temps that never go below 65°F, but I think it is unnecessary, and most of the experts I've spoken with agree. If used, I would change in time for cooler winter weather.
>> As for oil consumption my '93 has 205k miles on it and doesn't burn or >> lose a drop of oil, over 3000 miles so far the dip hasn't moved at all.
This is normal for a Saab. Of five I've owned, none have ever used any measurable amounts of oil between changes.
, Sat, 17 Feb 2001 13:57:08
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