http://articles.sun-sentinel.com/2011-09-2...omotive-serviceTL;DR
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Different manufacturers have different names for severe duty. Ford, in a recent F-150 pickup manual, lists a "normal schedule" for maintenance and a separate schedule for "special operating conditions." If you tow a trailer, use a car-top carrier, idle a lot in stop-and-go traffic or drive frequently in dusty or sandy conditions, Ford suggests changing the oil and filter every 3,000 miles. Under the "normal....
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aren't driven enough, or are seldom driven at speeds that allow for an engine to heat up to a level where moisture is baked out of the...
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age and usage are even more important in determining what the right service intervals are for your vehicle. You take any vehicle that has fluid that is bathing metal parts, and it will soon begin to develop acid, and if enough acid builds up, the fluid will eventually start attacking the component it was designed to protect.
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When electricity is constantly applied to transmission fluid, it can build acid, almost like a battery. It accelerates wear and pitting.
This is what they define as "severe" usage, which apparently requires more frequent maintenance.
This post has been edited by TDUEnthusiast: Sep 26 2013, 11:16 PM