Synthetic Oil VS. Regular

I bought my used Montero off eBay and got 18.1 mpg religiously till I got my first oil change.
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That's when I remembered that the seller had told me he changes with synthetic oil. Well, I realized it when my mileage dropped to 16.5 mpg after that change. It is hovering about 1.5 mpg less now with no other changes. Tire pressure is constant, driving habits unchanged, weather the same, etc.

I did some research and found this Mobile 1 oil that guarantees 15,000 miles till the next oil change. I am NOT a mechanic or even that handy, but I can use a calculator. Here's my math question:

If I drive 30,000 miles and change my oil twice with synthetic or 10 times with regular off the shelf oil, which one costs more (or if I do the regular oil on 6 intervals)? Assume 5 quarts of oil at $5.99 per quart for the 15k mobile 1 and $1.50 per quart for regular oil. Also assume a special filter for $12 for the mobile 1, a regular filter $8 for the other at each change. The cost of labor & disposal SHOULD NOT BE DIFFERENT so call it $12 per change.

Cost of servicing on 30,000 miles:
Mobile Synthetic Extended: $108.00 / gallons gas: 1657.48
Cheap oil every 3000 miles: $275.00 / gallons gas: 1779.36
Cheap oil every 5000 miles: $165.00 / (assume same as 3k)

If you average 1.5 mpg better with the synthetic: add $300 savings to that difference!

I am shocked at the savings using the high mileage synthetic! Eliminating the extra changes is a huge difference! If you only get 1 mpg better fuel that would be $200 savings! Well worth less effort for less frequent changes. IF you try another synthetic with a lower mileage you would still see a big difference if you got the fuel savings.

To get these savings, you'll have to do your homework. To be safe: buy the oil yourself and take it to a mechanic. Those quick lube places really do a number on charging for the synthetic changes and you don't even know if they really did put the synthetic in.

Let me know if it works for you?

Interesting reading:
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