Synthetic Lubrication and Fuel Mileage? Why?
If I've heard it once, I've heard it a thousand times, synthetic lubricants get better fuel mileage because they are more slippery and with less friction you get better mileage. Really? If that were true, then using petroleum base lubricants would cause extreme wear! Is this the case? Really?
Back in the late 70s or early 80s, legendary auto mechanic and mechanic tech article author the late Smokey Yunick used a synthetic motor oil from a company that has since gone out of business. This company was created by someone wanting to duplicate the success of AMSOIL, but ultimately found the chemistry more complex than they imagined. They had neglected to add a friction modifier additive that is important for wear prevention. Smokey reported better horsepower and performance and was very enthusiastic about this new oil technology. That is until his camshaft failed due to excessive wear. Later Smokey discovered AMSOIL and became one of their best promoters witting numerous articles about the benefits of synthetics. But before that, he was disappointed at how the first experience he had with a synthetic motor oil showed improved power and performance, but proved destructive to his engine.
But wait . . .how was this possible? How could Smokey get better performance yet see destructive wear? Isn't the better mileage and performance of a synthetic due being more slippery? If it is more slippery, then how did the engine wear out? Apparently it's something other than friction that creates the better performance you see with synthetics now isn't it?
I've heard it over and over again that the reason you get better mileage with synthetics is due to less friction. I've even heard some AMSOIL Dealers make this statement. While a properly blended lubricant can have less friction and less wear, this isn't as dramatic an influence on power and performance as you might think. The truth is that there are several reasons why synthetics provide better power and performance. Most people don't care why, just like the "cheap horsepower" and "cheap insurance" as recently stated on one of those auto performance tech shows you see weekends on Spike TV. There are a lot of reasons synthetics improve mileage and performance and reducing friction is just a small part of it.
To understand the reasons synthetics provide better performance you have to study the differences. Both petroleum and synthetic lubricants can use the same additive technology, even though synthetics tend to use more expensive additive technology because they are already in a higher price bracket, so selecting more performance oriented additives tends to be a no brainer. But the main reasons for synthetic lubricants improved performance lies in the differences in their base oil which is synthetic instead of petroleum. The base oil in a modern lubricant carries the additives which do all of the work making the lubricant the marvel of technology we all take for granted, especially in motor oils which do a lot more than just lubricate. The base oils in petroleum contain paraffin and sulfur which negatively affect several different aspects of motor oils. Here's why:
Paraffin gels up really bad when the lubricant gets cold. This is why petroleum motor oils must have additives known as Viscosity Index Improvers (VI) which keep the paraffin molecules from gelling up as the temperature drops so an engine dry runs less on cold start up. The longer an engine dry runs, more severe engine wear will occur. Also, even after lubricant flow is established, the petroleum motor oil tends to be thicker requiring more horsepower to pump it until it is warmed up. Synthetics flow instantly due to the fact that they don't have paraffin and for the same reason don't usually have any VI additives. There is a limit though. If you see a synthetic that is 5W-30, 10W-40 or even 20W-50 you can assume it is a straight weight in that it can be blended with no VI additives and still not thicken when cooled so it passes the cold "W" or winter ratings at the colder temperatures. This means instant lubrication on cold start up. However, if you see a synthetic with a 5W-50 viscosity rating, it will have some VI additives since not even a synthetic can be stretched this far across the temperature scale. Some people consider VI additives a potential problem since they tend to shear back under stress and heat, so the less use of these additives the better. Of course you don't want to dry run on start up either, so we must accept the use of VI additives in petroleum. We can avoid them entirely using synthetics by avoiding the 5W-50 viscosity ranges.
The next reason for better mileage and performance of synthetics tends to be the pollutant known as sulfur which is in petroleum motor oil. There are additives added to all motor oils, including synthetics, that prevent the oil from becoming corrosive and to prevent soot and combustion by products from developing into larger and more abrasive particles. These additives are known as Total Base Number additives or TBN. As the TBN additives do their work they become depleted. In a used oil sample sent to a oil analysis lab to be spectrochemically analyzed, the TBN will have a number which represents how much of the additive is present. When the TBN number gets depleted down to a number of 2 or below the oil must be changed even if the oil is otherwise clean. This is because the TBN additives are the additives that maintain oil cleanliness and purity and once depleted the oil can no longer be trusted to do its job. Normally for gasoline engines the oil's TBN starts out somewhere between 6 and 10 depending on which oil and who manufactured it. For Diesels the oil's TBN starts out at 10 to 15 TBN depending on who manufactured it. AMSOIL targets 12 as the TBN for its gasoline synthetic motor oils and 15 for its synthetic diesel motor oils. That being said, as oils age the TBN number drops as the pollutants use up the TBN additives. A petroleum motor oil with 3,000 miles on it, depending driving conditions, after chemical analysis can show a TBN of less than 3 to even 0 while a synthetic can have 15,000 miles driven under the same conditions showing a TBN of higher than 6. The reason is the petroleum base stock deteriorate faster and the sulfur accelerates this process stressing the TBN additives more. Synthetics are more thermally stable and this shows up in how slowly the TBN additives are used up. In the final analysis, the petroleum will change chemically the longer it is driven requiring more horsepower to pump and move it about in the engine while the synthetic maintains like new properties. This averages out to be improved mileage and performance.
Last but not least, there is more power required to move petroleum oil through an engine or transmission. It's not just the oil pumping system, but the way the lubricant impedes the action of moving parts. When a piston moves up and down in the cylinder it scrapes and spreads the motor oil. The bearings turn and the oil being pumped through the bearings is hydrodynamically impelled around the moving parts by the high speed turning. In a transmission the gears and bearings impel and "squish" the oil from tight places. Synthetics require less power to impel than petroleum for two reasons. The paraffin in petroleum in a hindrance for one. The second reason is the fact that the molecular structure of petroleum in an average of so many dissimilar materials averaging out to be what's in the petroleum oil base stock. This tends to be less easy to move under loads. Synthetics are made chemically to be uniform and therefore less reactive chemically so as to last longer, but the side benefit is they require somewhat less power to impel about engines and transmissions and the absence of sulfur means the performance stays peak without the steady decline seen in petroleum based oils. This is the reason Smokey Yunick's engine had so much wear with an improperly blended synthetic motor oil, yet showed improve power and performance. It's all in the base stocks that the oil starts with.
I've had people who know little about synthetics, but use wear metals in used oil samples as a reason for not expecting better performance out of a synthetic. Most people seem to have used oil samples from Royal Purple brand synthetic motor oil, for some reason, and compare them to some samples they have taken of petroleum oil showing wear metals to be about the same. I have to educate them that wear isn't a test of motor oil performance. If they put that same synthetic motor oil to an engine test using an engine or chassis dynamometer they'll see better power output. It's about more than wear, it's they way the lube moves about the engine and how much resistance the lube gives the the moving parts.
Of course I get out my used lube samples of AMSOIL and show then how slight wear metals can be. I have more information online about the difference in wear metals in used oil samples with tests done on Highway Patrol cars here in Texas. In the Texas Department of Public Safety test comparisons between AMSOIL and petroleum motor oils in Highway Patrol cars, the AMSOIL used oil sample that had nearly 25,000 miles without being changed had slightly less wear metals than the petroleum sample with just a little less than 1,800 miles! Highway Patrol cars are an extreme test of a motor oil since these cars are driven hard and do a lot of engine idling which doesn't move the odometer. Sometimes these cars will see shift changes without shutting off the engine. Ironically, the Texas DPS wasn't interested in performance improvements such as better fuel mileage. Instead they were trying to save money on maintenance and the extended oil drains saved them several hundred dollars per vehicle per year. For more information see this article:
Texas Highway Patrol Cars Using AMSOIL (Opens in a new window)
Lastly, what I've been talking about are true Polyalphaolefin (PAO) synthetics known as Type IV lubricants. These are hard to find if you buy from major oil companies. Mobil 1 is the last major oil company to still use them as of this witting. All others, with the exception of smaller companies like AMSOIL and Redline, the major oil companies have switched to a Type III petroleum based motor oil and call them "synthetic" through a legal loop hole. Type III lubricants are 100% petroleum with the sulfur refined out. These oils last longer without the sulfur, but still have a lot of the same performance problems associated with regular petroleum based oils. The must employ VI additives for one. Another drawback is the irregular mix of petroleum that averages out to be your motor oil and don't perform to the higher level of true PAO based synthetics. So how do I know if I have purchased a true PAO synthetic? If it's from a major oil company and not Mobil 1 then it's not a PAO. AMSOIL makes about 30 different motor oils. Of them there are 4 with the XL-7500 name on the label and are short drain Type III based petroleum. Even though AMSOIL uses the "legal loophole" and calls them "synthetic" they are not true synthetic and the reason for the short advertised oil drain. You see these XL-7500 AMSOIL motor oils in auto parts stores and quick oil change centers. They cost a little less therefore making them a good choice in that market. I would advise on shelling out the extra dollar per quart for the PAO based AMSOIL. You'll be happier with the results and it would be cheaper in the long run considering the price of fuel today and the improvement in fuel mileage.
See the following articles for more technical information on Lubricants including Motor Oil. All open in a new window.
Why does Motor Oil Deteriorate?
Change Engine Oil Light (How do these systems work and how good are they?)
Motor Oil Quality Progresses With Engine Technology (Good information on motor oil service ratings)
A Closer Look at Drivetrains (Gear Lube service ratings explained)
Don't Forget The Gear Oil! (Explains Gear Lube technology and outlines proper maintenance)
Change Gear Lube After Break-in Period for Long Differential Life
