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0W40 or 5W40 Posted by sam96CS [Email]  (#852) [Profile/Gallery]
(more from sam96CS) on Tue, 10 May 2011 19:44:01
In Reply to: Oil weight recommendations for viggen??? 40 ... 50 ??, Nathan Pflaum [Profile/Gallery]
, Tue, 10 May 2011 06:39:02
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Start with the owner's manual, but don't stop there because car manufacturers are under pressure from the EPA to increase fuel economy and reduce catalytic converter wear. We're all in favor of higher MPG and parts that last forever, but what if your #1 goal is to minimize engine wear?
There are 3 viscosity numbers you need to consider.
First, the number before the W which indicates how thin the oil is when it is cold. All motor oil is too thick when cold, and that is the reason why most engine wear occurs when engines are warming up. The lower the number before the 40, the thinner the oil and the quicker it will reach vital parts after starting a cold engine. By the way, you should not assume that your oil is fully warmed up at the same time that your engine coolant is warmed up.
Second, the number at "normal" operating temp., which for oil is around 212F. Here you should think carefully and weigh a lot of information before second guessing the highest number in the owner's manual. And I have second guessed Ford's spec for my '01 Mustang GT (long story).
The most important viscosity number for an engine at normal operating temperature is the HTHS (High Temperature High Shear) viscosity at high stress locations where the normal oil temperature is around 300F. It is often hard to find the HTHS number for a given oil.
For example, I don't know the HTHS number for the oil I'm using in my Saab engine, Shell Rotella T6 5W40 synthetic. But I know it is rated heavy duty, and I know that per SAE standard J300 it must have a minimum HTHS of 3.7 cP. Which is a respectable number and higher than you'll get with a 30 weight oil unless you're running something like Redline 5W30 synthetic that isn't sold where most people buy motor oil.
, Tue, 10 May 2011 06:39:02
, Mon, 16 May 2011 12:44:33, Tue, 17 May 2011 09:15:36, Wed, 18 May 2011 08:06:01, Thu, 12 May 2011 11:32:59, Tue, 10 May 2011 19:44:01 <-- Viewing This Message, Tue, 10 May 2011 21:34:21, Wed, 11 May 2011 05:59:04, Tue, 10 May 2011 09:40:37, Tue, 10 May 2011 10:11:16
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