Should I Run Multi-Weight or Straight-Weight Oil in my Muscle Car?

Ed Newman (Edited by Ches Cain)|Jan 12, 2016 4:30 PM

Much of the stigma related to this has been eliminated due to technology.

Here’s the straight story on viscosity grade. The “W” number in, for example, a 15W-50 motor oil outlines the viscosity requirements of the oil when it is cold. This means that a 15W-rated oil has to meet certain criteria at cold temperatures. Taking our 50-weight example, a 15W-rated oil will flow more freely than a 20W-rated oil when compared at cold temperatures.

Winter weights have always confused people. Don’t be afraid of the W!

If you have a spec that calls for a 20W-50 but all you can find is a 15W-50, don’t sweat it. That just means it will have better flow at a lower temperature. Or as I tell people, at room temperature it’s closer to its operating viscosity than a straight weight. Or a 10W-30 is closer to it’s operating viscosity (30) than a SAE-30, and a 5W-30 is closer to its operating viscosity than a 10W-30. But the “W” is not the same type of number or scale as the 2nd number. A 10W-30 is NOT a 10 weight at one temp then a 30 at another!! the 10W, or 20W is a totaly different test measuring toque absorbed at a given temperature range. The large number calculated is converted into the range which is your 5W and 10W and so on. A 0W is not a Zero Weight oil.

Now let’s talk about the “50” portion of a 15W-50, 20W-50 and straight SAE 50. The Society of Automotive Engineers (SAE) states that a 50-weight oil must have a viscosity at 100°C above 16.3 cSt but less than 21.9 cSt and have a high-shear-rate viscosity minimum of 3.7 at 150°C. This means that a 15W-50, 20W50 and SAE 50 weight must all meet these requirements. This does not mean they respond the same but they all need to meet these requirements regardless to have the 50-weight designation. Technically a 50-weight is a 50-weight at operating temperature no matter what the W designation is.

There is a LOT of confusion with these numbers. A little research will fix that.

Against this backdrop of understanding, the question is, should you run a multi-weight or a straight weight in our example? The answer is, take a close look at the oil specifications and compare to what you want to do and pick an oil that fully meets your needs. The best question to ask is, how does the oil hold up under shear”? Shearing is the loss of oil viscosity during operation. Shear is especially a problem when running engines at high RPMs.

Now no matter the age of the engine, when you use a straight weight oil there is some risk based on the quality of the brand. Outside of the normal operating temperatures, any degree below – lets say 75 degrees Fahrenheit, the oil will rapidly increase in viscosity. Starting an engine with a oil lacking the ability to flow as well as another also increases the likely hood to shear. Multi-viscosity oils solve this issue. And these days, the lower the “W” test value, the more advanced the product.

Consider what determines quality at various levels

The quality of the motor oil brand determines how many cycles under stress the motor oil can withstand before sheering out to a undesired viscosity. In some of these companies, the quality of the additives is determined by the profit margins demanded by the stockholders. (AMSOIL by the way, has no stock holders.)

Typically, muscle car folks will have a tendency to run up the rpm from time to time, which can shear down the oil viscosity. Viscosity is one of the most important factors for overall engine protection. When oil viscosity at operating temperatures degrades significantly, engine protection will be compromised. On the other side of the coin, if you start and run your muscle car in colder climates, a multi-weight will definitely provide more oil flow to critical parts quicker. Remember, most engine wear on automobiles actually occurs on startup when engine oil is not flowing readily to engine components.

So there are applications for straight weight oils but automotive engines are no longer in that category. Take advantage of the reduction of stress multi-viscosity oils offer. Muscle car owners want to feel the power at the wheels and a smooth engine. You want the oil to be optimum at all temperature ranges and even after a long trip.

Viscosity selection tip: pick a multi-weight oil that has outstanding shear stability. I personally always recommend AMSOIL. – The one motor oil with a guarantee to stay in grade!

By the way =

Gasoline is the source of your vehicle’s power – and many of its problems.

Gasoline quality is vital, yet often overlooked.

Dan Peterson - AMSOIL Technical Development

AMSOIL’s Dan Peterson.

Dan Peterson | VICE PRESIDENT, TECHNICAL DEVELOPMENT

Gasoline’s influence on our lives can’t be overstated. Remember how the gas lines of the 1970s disrupted daily life? People waited hours to fill up – if there was any gas available once they finally pulled up to the pump. Odd-even rationing dictated that motorists could only fill up on even-numbered days if the last digit on their license plate was even. The fallout of the gas shortages of the 1970s was a driving force behind the government mandates to increase fuel efficiency that continue to influence the industry today.

A few years ago, when gas hit $5 a gallon in some places, stories populated the Internet and airwaves about people willfully losing money to sell their giant SUVs in favor of small, fuel-efficient cars. Some people even took a loss on their houses in the suburbs to move closer to work.

In many ways, gasoline makes the world go ‘round, yet many of your customers likely know almost nothing about it, including the negative effects it can have on their vehicles.

Gasoline is distilled from petroleum crude oil. Typically, a 42-gallon barrel of crude will yield about 19 U.S. gallons of gas. The final blend can contain hundreds of different ingredients, among which are detergency additives designed to prevent harmful deposits from forming inside your engine.

In 1995, the EPA introduced its minimum gasoline detergent standard, known as lowest additive concentration (LAC). The intent was to ensure that all gasoline available in the country contained sufficient detergent additives to combat formation of deposits that reduce fuel efficiency and performance.

The widespread use of electronic fuel injection in the 1980s was a driving force behind the introduction of the LAC mandate. It quickly became evident that fuel injectors were especially sensitive to deposits, and the gasoline of the time didn’t contain sufficient detergents.

Deposit formation on the injector tips disrupts the spray pattern, which reduces fuel economy and results in less-efficient combustion. This contributes to increased tailpipe emissions since unburned gasoline can escape the combustion chamber on the engine’s exhaust stroke.

Deposits can also form on the intake valve, piston crown and in the ring grooves. They can prevent the intake valve from closing completely, reducing engine compression and horsepower. Deposits in the ring grooves can lead to ring sticking, which also reduces engine compression since a stuck ring won’t seal the combustion chamber completely. Piston crown deposits act like a sponge that soaks up gasoline. This can result in preignition, where the fuel/air mixture ignites sporadically, reducing performance and potentially damaging the engine.

Many automakers today don’t think the LAC mandate goes far enough. In fact, many gasoline marketers have reduced detergent levels by up to 50 percent, according to www.toptiergas. com. TOP TIER Detergent Gasoline is a performance specification designed by several of today’s top automakers.

Today’s vehicles run even hotter than they did in 1995. Since then the number of engines that use turbochargers, which increase heat, has grown substantially. So, too, has the number of vehicles that use direct fuel injection, which locates the injectors directly in the combustion chamber, exposed to intense heat. Plus, injectors today are more highly engineered with tighter tolerances, meaning even minute deposits can interfere with performance.

Gasoline is the source of your vehicle’s power – and many of its problems if you don’t perform proper maintenance. We formulate AMSOIL P.i.® to be one of the most potent additives on the market. It contains a very high dose of fuel detergents proven to combat the problems associated with gasoline, keeping injectors clean and functioning properly. In fact, testing showed dirty injectors returned to >95 percent flow after only one tank of gas treated with P.i. Just take a look at the dramatic before/ after images above.

As vehicles become more sophisticated and sensitive to gas quality, make sure you understand the importance of maintaining them with a quality fuel additive. AMSOIL provides solutions to problems you may not even be aware of.

Let AMSOIL Sioux Falls be your gasoline fuel additive source! Depend on us for the best products which will always be the state of the art for all Nebraskans! Thank you for your business. We love being here in Sioux Falls!

Category: Sioux Falls Motor Oil and Lube News