Technology Run Amok? - Part 2
Lubricating oils of both mineral (petroleum) and synthetic types have a quality index known as the SAE viscosity grade (in the US/Canada/Mexico markets). To these oils there are 4 types of additives:
- Vicosity Index Improvers (VI-used to change the viscosity curve under temperature increases)
- Oxidation & Corrosion inhibitors (to reduce the acids and alkalis form the byproducts of combustion and atmospheric conditions)
- Detergents & Dispergents (to “scrub” the dirt off components and disperse them into solution)
- High Pressure Additives (added to increase the shear strength of the oil under loading, abbreviated as “EP”)
Heat as a factor in Lubrication breakdown:
Heat from the engine combustion and friction causes the engine oil to lose viscosity. Synthetic oils are formulated to reduce this effect and widen the flowable temperature range.
Synthetic oils, as a polymer, are formulated to cover a far wider range of viscosities and mineral oils are capable of handling. For example the SAE standard oil viscosities are as follows:
| SAE_Viscosity_Value | Apparent_Viscosity@-18C_mPa*s | Kinematic_Viscosity@100C_mm2/s |
|---|---|---|
| 5W | …..1250 | 3.8 min. |
| 10W | 1250….2500 | 4.1 min. |
| 15W | 2500….5000 | 5.6 min. |
| 20W | 5000….10000 | 5.6 min. |
| 20 | - | 5.6 min. - less than or equal to 9.3 |
| 30 | - | 9.3 min. - less than or equal to 12.5 |
| 40 | - | 12.5 min. - less than or equal to 16.3 |
| 50 | - | 16.3 min. - less than or equal to 21.9 |
As you can see from this table, there is a point between 15W and 20 weight oil that is a “sweet spot” where the kinimatic viscosity is nearly flat. Synthetic oils (remember this chart is the SAE standard, and as such, was developed for mineral oils, NOT synthetics)
extend this spot to almost their full range, depending on the oil manufacturer. For this reason, Chrysler chose Mobil 1 synthetic for the Viper v10 engine. Under extreme heat, pressure, and shear, Mobil 1 performs more consistently than any other oil tested.
By reducing the friction, fuel used to overcome the friction is also reduced. On average, the difference is small, 1-2.5%, but, when combined with increased longevity and other factors to be discussed, these seemingly insignificant increases will reduce fuel costs.
COMMENTARY:
The costs of such changes are not insignificant to most people, and will be discussed later in this series.
From a personal standpoint, I ran Mobil 1 in my Ford Thunderbird V8 from 1996 through 2000. During this time I accumulated 129,000 miles on the car. By carefully monitoring the oil status, and having regular oil analysis performed at a cost of 19.95 each time, I increased the change
interval to 15,000 miles for the oil. Losses included a filter change every 3000 miles plus at every complete oil change, plus 1 quart of oil burned/leaked every 12,000 miles. At the last engine leakdown test performed at 110,000 miles, there was less than 5% engine compression
leakdown total.
