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, Wed, 8 May 2002 01:26:13
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that engine metals and synthetic oils haven't changed "drastically" in 20 years. How do you define drastically? Metallurgy (as applied to engines) has made incredible changes in 20 years. I don't know if it's made its way to SAAB engines, but others have benifitted from them. Engine oils are very different now than 20 years ago.
The relief valve on a filter should typically only bypass oil on three occassions (this is per Mike G, a retired oil company chemist, and an avid VFR750 owner. Anytime you want to find out about anything, visit the VFR email list archives, a more knowledgeable group probably doesn't exist http://www.cs.wisc.edu/~john/vfr-list/ )
1. One example is when you start the motor when cold. The oil is thick and does not pass easily through the filtration medium, thus building up to a high pressure drop. So, the bypass valve opens to prevent oil-starvation of the motor. How long it stays open is dependent on how cold the oil is and how long it takes to get near operating temperature. When the pressure drop across the filtration medium drops below the bypass valve setting, then the bypass closes. Blipping the throttle while warming up is a good way to get the valve to open and send unfiltered oil to the motor. A steady warm-up rpm is probably a lot better.
2. Another example can occur when the motor is fully warmed. At idle, the oil pressure is about 15 to 20 psi, and the pressure drop across the filter is about 1 or 2 psi. You take off towards the redline, and quickly build oil pressure to the 70 to 80 psi range. During that full-throttle acceleration the pressure drop across the filter will exceed the bypass setting, and send unfiltered oil to the motor, until the pressure across the filter has time to equalize. During a drag race, shifting through the gears, the bypass will open several times.
3. A third example, which you should never experience with frequent oil and filter changes, is when a filter becomes clogged. A spin-on filter can commonly hold 10 to 20 grams of trash before it becomes fully clogged. The bypass valve opening is the only way to keep the motor from becoming oil-starved if the filter becomes clogged.
Note: the oil pressures listed in #2 apply to VFR's, not sure what SAAB's experience.
But basically you're saying, use synthetic oil and change filters 4 times as often as SAAB recommends?
Ed 2002 Aero SW 1998 VFR800 Fort Wayne, IN
posted by 66.84.139...
, Wed, 8 May 2002 01:26:13, Fri, 10 May 2002 00:26:07
, Sat, 4 May 2002 12:31:52
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