We’ve published articles on the new crop of — and specifications for — ultra-thin OEM oils that are coming to market as of late. While it’s no secret that some of the top forms of motorsports have been using oil which is approaching water-weight for years, that was really such a small portion of the market, and such a specialty item, we never really worried about someone grabbing some zer-weight oil and putting it in their Camry.

However, with zero-weight oils popping up all over the OEM space, as well as a new 0W-16 oil being used for fuel economy, it’s much more likely that enthusiasts (yes, we’re talking to you) are getting some ideas about trying out some of these thinner oils in search of extra horsepower. For that reason, Jason Fenske of Engineering Explained decided to partner up with Mobil 1 and discuss these new ultra-thin oils, and what you shouldn’t be doing with them.

What The Numbers On The Bottle Really Mean

“Right off the bat, we need to clarify something,” Fenske starts out in his typical tone. “The term ‘weight’ isn’t all that appropriate to use, as the term doesn’t represent an actual weight measurement, but rather a viscosity measurement.” While there is a small difference in weight-per-gallon of highly-viscous oil versus an extremely thin oil, that has zero bearing on this discussion.

Explained technically, viscosity is a measure of a fluids resistance to flow. Explained simply, it’s the fluid’s thickness. “A thicker fluid like honey will have a higher viscosity than a thinner liquid like water,” Fenske explains. “Ensuring the proper viscosity is the single most important criterion of a motor oil. The higher the number on the bottle, the thicker the oil. But we have to remember those numbers are temperature dependent.”

This shows Fenske dropping a steel ball-bearing through 5W-30 at room-temperature and at 32 degrees Fahrenheit at the same time, to illustrate temperature’s effect on oil’s viscosity.

Generally speaking, most of us will use a multi-grade oil. That is something that reads as “XXW-XX” on the bottle. That first number, with the “W” (which stands for “winter” not “weight”) is the “cold” viscosity, and the second number is the “hot” viscosity “No, that doesn’t mean the oil gets thicker as it heats up. It means that it behaves like a thicker oil, at higher temperatures,” says Fenske.

“Comparing a 10W-30 oil to a 0W-40 oil (like what comes in the LT2), when cold, the 10W-30 will be thicker than the 0W-40. However, at elevated operating temperature, the 0W-40 has a higher viscosity than the 10W-30.” To achieve such witchcraft as a multi-grade oil, you would typically start with a lower-viscosity base oil, and then jump into the oil additive packages — specifically viscosity modifiers — to alter the oil’s performance as it heats up.

“To determine the oil’s viscosity at both the low and high-temperature measuring points, there are a number of ASTM tests the oil must undergo,” Fenske Explains. “The cold tests take place at -10 to -40 degrees Celsius (14 to -40 degrees Fahrenheit) and are more geared towards making sure the oil will move when cold. The second part of the rating is based on measurements taken at 100 and 150 degrees Celsius (212 to 302 degrees Fahrenheit). Those tests are more aimed at seal leakage and the oil’s behavior when in a very thin film.”

Thin Oil’s Effect On Efficiency

Racers have known for a long time, that a thinner oil is good for some extra power on the dyno and at the racetrack. It’s a relatively simple concept once you understand it, but sometimes, truly understanding what’s happening with oil can be hard to wrap your head around.

“Generally speaking, the lower the viscosity numbers of an oil, the greater the efficiency [of the system it’s lubricating] is. That basically comes down to friction,” Fenske says. “If you think about dragging your hand across the surface of a container of honey, it’s slow and difficult. Now think about dragging your hand across the surface of water. It’s much easier and takes less energy to do. The same goes with your oil and the metal parts the oil is protecting.”

The exact gains are highly specific to the individual system being tested and the components involved. But there are some rules of thumb out there. “I’ve see studies that moving from a 30-weight to a 20-weight oil can result in a one-percent increase in efficiency, with the same increases going from a 20 to a 10,” explains Fenske.

“A fraction of a percent of efficiency increase might not sound like a lot, but when you consider how efficient today’s engines are, raising an internal combustion engines efficiency from 40 to 41-percent is a big problem to solve. Oil viscosity an play a large part in that one-percent target.”

Thin Oil And Engine Protection

Since drag racers are only running their engines for a burnout and a quarter-mile pass at a time, many people associate zero-weight oil with that, it’s easy to just assume that they can get by without proper protection, but that would be an incorrect assumption. In fact, if an engine is built around a zero-weight oil, there is no reason the thinner oil will measurably shorten the powerplant’s lifespan.

“With modern engines, component wear is not usually a limiting factor. Companies have done an extremely good job of figuring out how to make the internals of engines last. Fuel economy is a bigger challenge for them,” says Fenske.

“If everything [in the engine] is working properly, and you have the correct viscosity oil in the engine, there really is no metal-to-metal contact, as long as your oil pump is maintaining pressure, and your oil is in good shape. There are instances, liike on start-up, where you don’t have the full oil film, and that’s when the anti-wear additives in the oil are useful.”

However, the key factor here to remember is that you can’t just go out and drain your 10W-30 and toss in some 0W-16 and pick up power and/or fuel economy. The tolerances and clearances in your engine are designed specifically around the manufacturer- (or builder-) recommended oil viscosity.

“Generally speaking, lowering the hot rating of your oil is bad. Going the other direction and increasing the hot rating from your recommended oil isn’t as bad, but is still not recommended. If you are putting excessive heat into the oil, like at track days, a higher hot number can be indicated in those situations,” says Fenske.

“For the cold rating, if you went from a 10W-30 to a 5W-30, you aren’t really changing much, since the entire viscosity range of 5W-30 is within the 10W-30 specifications. On the other hand, going from a 5W30 to a 10W-30 will have your engine seeing a much thicker oil on startup, with no benefits at operating temperature.”

Hopefully, that gives you some insight into the new ultra-thin oils on the market and helps make sense of a subject that many struggle with, whether they’ll admit it or not.