All about oil

Should you consider using a synthetic?

If you lease your car, buy a new car every year, or could not care less about mileage or engine longevity, do not use a synthetic. If, on the other hand, you do care about your car (or live where the winters are cold), using a quality synthetic can provide you with some very real benefits.

Let us look at the economics of using a synthetic. In this comparison, the mineral oil is a typical SG-rated motor oil, and the synthetic one of the highest-priced lubricants you can buy.

As you can see from the table below, we are assuming you can buy the mineral oil at the bargain basement price of 45 cents. The synthetic in this example goes for eleven dollars per quart. Quite a difference!

Because this synthetic is a long-drain oil (50,000 mile recommended interval), you fill the crankcase once and change only filters at your normal oil change interval. Every time you change the filter you top off the crankcase to replace the oil you lose in the process of removing the filter. In the table, it is assumed that you add one full quart per oil change. This allows for some oil consumption.

The number of oil changes in 50,000 miles is different for the two oils, but the number of filter changes is the same. The cost of the filter is the same no matter which oil is used, as is the labor cost. These costs are omitted for the sake of clarity. The cost of fuel per gallon is the same for both oils, but the synthetic offers to increase mileage 10 percent, although the we used 5 percent for this comparison. The cost for overhauling the engine is the same for both motors, but the synthetic oil claims to double engine life (we allowed one-third greater engine life for this comparison), so the cost of wear per mile is less.

The last four lines are the most important. The total savings of $223.31 may not seem like a big deal over 50,000 miles. But notice that with the fuel and engine wear savings, there are $12.41 in benefits over and above the $11.00 cost of the synthetic. When extra fuel consumption and engine wear costs are added to the mineral oil, the true cost turns out to be $4.02, much higher than the bargain 45 cent purchase price. The last line shows you would have to pay $23.41 for the synthetic to negate the mileage and engine wear benefits. To look at it another way, you could use twice the normal amount of this synthetic and still be ahead of the game.

In comparison to the example shown in the table below, if you were to change your oil more often, buy cheaper fuel, and overhauls were less expensive, the savings would be reduced. Abnormal oil consumption also cuts savings. However, more expensive fuel and costly overhauls make the savings skyrocket.

Computing of True Cost of Using an Oil
  Conventional oil Synthetic oil
Purchase price (per quart) $0.45 $11.00
Number of quarts per full oil change 5 5
Number of full oil changes in 50,000 miles 10 2
Number of quarts per filter-only change 0 1
Number of filter-only changes in 50,000 miles 0 8
Cost of fuel (per gallon) $1.25 $1.25
Miles per gallon 20.0 21.0
Expected engine life (in miles) 100,000 133,333
Cost of an engine overhaul $2,000.00 $2,000.00
Total cost of oil changes $22.50 $198.00
Cost of fuel used $3,125.00 $2,976.19
Amortized engine costs $1,000.00 $750.00
Net savings over 50,000 miles   $223.31
Added value of synthetic oil per quart   $12.41
Real cost of conventional oil per quart   ($4.02)
Parity price for the synthetic   $23.41

To demonstrate, look at an engine that is more expensive to overhaul ($6,000 vs. $2,000), if you get 10% mileage improvement and a doubling of engine life, your total savings work out to $1,608.59 over the course of 50,000 miles, with $89.37 in added benefits per quart of synthetic (over and above the purchase cost), while the true cost of the bargain conventional oil is $31.72 per quart. To achieve parity with the cost-to-benefit ratio of the conventional oil, you would have to pay $100.37 per quart for your synthetic.