Synthetic Motor Oil, How?

In previous posts, we covered what a synthetic motor oil is, and why you might want to use it. Now we consider how it is different from from conventional motor oil. The procedure for how to change motor oil, covered previously here on Family Trivium, is the same as for conventional motor oil – you should, simply, need to do so less often.

How Is Synthetic Motor Oil different From “Regular” Motor Oil?
Aside from the obvious fact that mineral oils come from the ground and synthetics from the lab, we can learn from the Bob Is the Oil Guy’s Oil 103 class how these two substances are operationally different, particularly when considering multi-grade products:

Multi-grade mineral oils are based on a lighter weight oil, with the intent of better protecting an engine at startup than a heavier weight oil that would be at an optimal viscosity only at operating temperature. A “viscosity index improver” (VII) is added to this thinner weight oil to make it thick enough to provide optimal viscosity at operating temperature. It should be noted that even the lowest weight oils (straight or multi-grade, mineral or synthetic) cannot achieve an optimal viscosity at startup, when they are cold.

Multi-grade synthetic oils are based on a heaver weight oil, not requiring a VII to allow them to achieve optimal viscosity at operating temperature. At lower temperatures, synthetic oils do not thicken as much as mineral oils, so they maintain a more desireable viscosity at startup.

In the example from our original Motor Oil post, our Ford uses 5W-20. A conventional 5W-20 is based on a 5 grade mineral oil and has VIIs added to give it the higher viscosity of a 20 grade motor oil at operating temperature. A synthetic 5W-20 is based on a 20 grade synthetic oil which still manages to be thinner than mineral oil when cold.

In Bob Is the Oil Guy’s Motor Oil 104 class, further argument is given for why synthetic oils protect better than mineral oils:

  • They have a higher film strength, so they do a better of job of sticking to engine parts, helping to prevent wear at startup.
  • Engines using synthetic motor oils turn over easier
    • Thus, the starter is less taxed and will last longer, and
    • The battery is less taxed and will last longer, because
      • The battery is discharged less at startup, and
    • The alternator spends less time recharging the battery, which uses engine power otherwise used to move the vehicle, and
      • The alternator is less taxed and will last longer, and
    • You will get better gas mileage because the power of the engine is being used to move the car forward rather than recharging the battery.

Last Month, with this knowledge at hand, when we changed the oil in our Ford, we switched from the OEM-specified 5W-20 synthetic blend motor oil to a full-synthetic 5W-20. In addition to the reasons, stated in this post, of better startup protection and possibly better fuel economy, we also desired a longer oil change interval, thus we also installed an oil filter designed to go up to 15,000 miles (like the oil which was used). We don’t anticipate going 15,000 miles before changing the oil, but we are hoping to get as much as 10,000 and we are considering sending it in for a lab analysis to see if perhaps we could have gotten more life out of it. Look for future updates on this topic.