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Old 02-05-2005, 01:41 PM   #18
Scooby Newbie
Member#: 35732
Join Date: Apr 2003
Location: Denver,Colorado
2002 WRX Wagon


One factor owners often overlook is the percentage of highway miles driven versus city miles. Highway miles are *much* easier on your oil because you are driving a lot of miles all at once where your engine is fully warmed up, running at a steady speed, and not doing a lot of stop light idling like in the city. Repeated bouts of prolonged idling in city driving is very hard on your engine and your oil.

If 70%-90% of your miles are highway, you can easily go 6000-7500 miles between changes using Mobil 1. 7500 mile OCIs was what Mobil used in its famous million mile BMW test. But if most of your miles are stop and go in the city, better to change it at 3750 like it says in the manual under severe service. BTW, if you are running a turbo engine, many top mechanics say you are automatically in the severe service category regardless of how you drive.

Just to make things more confusing , here is a deceptively brilliant oil change formula devised by an Amsoil engineer that will give you a precise answer as to exaclty how many miles you personally should drive between changes. It is theory #5 down the page: Kublin Oil Change Method

(In using this formula, you may notice that as your gas mileage goes up, indicating more highway miles driven, your oil change interval increases significantly.)

P.S. All the opinions expressed in this thread are valid points of view . Good luck with whatever you decide!
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Last edited by rexaroo; 02-05-2005 at 01:57 PM.
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