Quote:
Originally Posted by Aufgeblassen
Synthetic 5W-40 motor oil will give you a few percentage MPG increase. It is WAY cheaper to use than legacy (petroleum) oil, because you can periodically do oil analysis, and find you can keep running the oil for many, many miles w/o an oil change. You only need to do filter changes every 30,000 miles or so along the way, and top off oil after a filter change. The farthest I have gone in my '01 Volvo w/ Volvo engine on a crankcase of oil was 150,000 miles. I saved a BUNCH of money and time.
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While synthetic oil is great in most cases, it may not be in your application with an older engine with so many miles on it. To determine if it will be cost effective, how much make up oil do you have to use and at what interval. Most healthy engines will use about a gallon at the 10K to 15K mark. If your's is burning more oil than this I would think hard about switching to synthetic. 5W oil is thinner than 15W oil and will slip by the rings and cause you to burn more.
You can try to blend your oil to test your oil consumption. One method is when you do an oil change use your current oil. Add synthetic as your makeup oil.
It is a good idea to use a bypass oil filter. It will keep your oil clean, change it when your samples indicate it needs to be changed. Extended oil change intervals because you oil bypass system is keeping your oil clean is what makes using synthetic oil economically feasible. Even if your engine burns too much oil for you to use synthetic it is still a good idea to use a bypass oil filter.