When you enter a parts store to get engine oil, you’re met with several different varieties. If it’s not the weight of the oil that leaves you confused, it’s the type of oil that might make you wonder which is best for your vehicle. How does an engine oil know if you’re racing, or cruising, or if you’ve got a hot rod, or a vehicle with lots of miles on the engine? What is viscosity, and how does it affect engine oil?
Many of us might choose an engine oil based on what our friends use, but how did they come by the decision to use the engine oil they’re using? Did they hear about it from someone else, or did they actually do some of their own research? These are all good questions, and we reached out to Driven Racing Oil to get some answers, and hopefully shed some light on motor oils.
Engine Oil Viscosity
There’s an easy way and a technical way to describe viscosity. The technical definition: Viscosity is an oil’s resistance to flow as measured on a viscometer. Of course, it is much more technical than that, but the easier, layman’s term is that it’s the thickness of the oil.
Viscosity changes with the temperature, and as the oil gets hotter it also gets thinner. A perfect example is shown in the video below where Lake Speed, Jr., shows how syrup flows quicker when it’s warm, and slower when it’s cold, and the same happens with oils.
You might notice that when your engine is cold the oil pressure is higher than it is when it gets warm. As the oil thins with heat, it will flow a little quicker, just like the syrup.
In order to determine the proper viscosity, you should find out the oil operating temperature first. For racing engines that run at hotter oil temperatures up to 300 degrees, a higher viscosity is recommended.
A lower oil temperature will allow for a lower viscosity, but using a viscosity rating that’s too high for your engine could result in excessive oil temperatures and increased drag. Using one that is too low can cause metal to metal contact of moving parts, so the correct viscosity should be chosen based on oil temperatures, not necessarily because you drive fast or rev higher.
But most oils today don’t have a single rating. Since the mid 1950s, multi-grade oils were created and they have two sets of number – such as 10W30. Prior to the existence of multi-grade oils, it was recommended to have a thinner, or lower viscosity grade, in winter time (the ‘W’ in 10W30) and a thicker oil for summer time. In addition to changing oil at regular intervals, the oil was also changed for winter months.
The winter rating (10W in this example) is a cold cranking simulator test that is done with the oil at roughly 30 degrees below zero. Typically, the lower viscosity is between 0W and 20W, and the lower the number is, the better it will flow at colder temperatures.
The second number (typically between 20 and 50) is the actual viscosity of the oil. These SAE grades are ranges. Meaning that an oil that has a kinematic viscosity between 9.5 centistokes and 12.5 centistokes is a 30 weight oil. For example, a centistoke is 1/100 of a stoke (named after George Gabriel Stokes), and one centistoke is the kinematic viscosity of water at room temperature.
There are two major things that dictate viscosity: operating oil temperatures and bearing clearances. If you haven’t built the engine, it’s difficult to understand what viscosity rating is required. -Scott Diehl, Driven Racing Oils
“For example, those who have experience and knowledge building engines would know that a small-block Chevy would be okay with a 30 weight, whereas a big-block Chevy would have different bearing clearances and might require a 40 weight,” he continued.
The bottom line is that choosing a viscosity is not something that Diehl says can be found on forums. “Forums are just opinions, not always fact, and more research should be done,” he said.
We’ve all had that friend, or someone on a forum that we’ve respected, and they might use a specific weight for their car, but do we really know the reason why they use that viscosity rating? Is it only based on what someone else used, or was there some real research behind it?
That’s why Diehl suggests that you call an oil manufacturer and tell them about your vehicle, and let them help you make the decision. Because the old days of buying an oil based on what our favorite motorsports personality endorses are long gone. Today, there is much more that goes into an oil that we can’t just use what someone else uses, we need to do our research.
Engine Oil Additives
Like anything else that we gearheads enjoy, you can always count on some entity, like the American Petroleum Institute (API) to throw us a curve ball. Today’s engine oils have started to conform to specific standards, and one of the additives that’s been reduced – or missing altogether – from today’s off-the-shelf engine oils is zinc.
According to Driven, the zinc in motor oils refers to a family of additives called Zinc DiakylDithioPhosphates (ZDDP). There are three types of zinc: primary, secondary, and tertiary, and they have different activation thresholds. Zinc does not become a lubricant until the ZDDP reacts to the heat and load, at which point it creates a phosphate glass film that protects metal surfaces.
But just adding zinc to an oil is not how you get the zinc to properly mix with the oil. “You basically become a chemist,” Diehl said. “If all you’re doing is pouring a zinc additive into the oil, you’re not properly mixing the two together.” One example of this that Diehl uses regularly is sugar and tea. He said, “What happens when you put sugar in iced tea? It sinks to the bottom, but if the tea is hot the sugar will dissolve better.”
Solubility is very important when you’re dealing with additives. We don’t just add zinc to our oils, some additives need to be added when the oil is at a specific temperature, and others at different temperatures. -Scott Diehl
“We engineer our oils for very specific applications, we don’t merely pour in additives,” he said. “Fifteen years ago you could use the same oil for just about every application, and you could use additives. Oils are so much better today that you don’t need those additives.”
But there’s a limitation on what oils work with specific applications. Zinc has been reduced, and detergents have increased for extra deposit control. Detergents will help reduce sludge and varnish, and modern engines may not require the same level of zinc additives as our old school performance builds.
How Important Are Zinc Additives?
From Driven’s website on zinc:
Zinc needs heat and load for it to activate and then lubricate the surface. Some types of Zinc activate faster under less heat and less load than other types of Zinc. These “fast burn” Zinc additives provide better protection during engine break-in because they react faster and establish that protective phosphate glass coating quickly during the critical break-in phase.
All three types of ZDDP function similarly, and because zinc is a polar molecule it’s attracted to steel surfaces. Zinc will react with the steel surface under heat and load to create that phosphate glass film. It forms a sacrificial film that covers the peaks and fills the valleys in the surface and protects the steel. But how much heat and how much load is required to activate the zinc depends on the type.
Secondary ZDDP is the most active, but it has been reduced in today’s engine oils because it is blamed for reducing catalytic converter life. Now there are newer, less active ZDDPs being used in oils to extend catalytic converter life, and that means that many of today’s oils have changed to meet those demands.
But Driven states that it’s not entirely a bad thing if you’re running a stock valvetrain without any performance modifications, and that the API grade oils are perfectly suitable for a modern street driven vehicle. But once you start modifying your engine for performance, these oils might not be the best choice for your hot rod or musclecar.
When you begin modifying your engine for performance or racing, that’s where zinc additives – and the amount – require some changes. These days, one oil doesn’t fit all applications, and specific oils are formulated to meet the needs of the engine based on several factors.
Higher lift cams with longer durations and greater spring pressures need a faster response from the Zinc. Oil development in race engines shows that faster acting Zinc Dialkyldithiophosphate (ZDTP) does a better job protecting highly loaded valvetrains.
Essentially, when you start modifying for performance, you’re out of the API guidelines that determine oil performance specifications. The other problem is that zinc is not the only additive in oils: there are detergents, dispersants, viscosity index improvers, and other additives that compete with ZDDP for surface space inside your engine.
Since 2005, the level of ZDDP has continually reduced and engine builders reported a number of cam failures, and began to seek oils with higher levels of ZDDP. For a while, diesel oils were used that contain a higher level, but they, too, underwent a reduction in ZDDP.
By 2007, the levels were reduced greatly, along with an increase of calcium detergents and dispersants, so much so that engine builders were reporting flat tappet cam failures. Many had switched to break-in oils that were high in ZDDP and low in detergent but were still unsure of what those levels were, and whether they contained the fast burn or slow burn ZDDP.
Break-In Oils, Racing Oils, And Synthetics
We’re often told that we should use a good break-in oil for a fresh build, and never use a synthetic. Diehl said, “With break-in oil, we lower the level of detergents and dispersants to allow the anti-wear film to establish quickly, thus reducing the amount of wear during this period which equates to longer part life.”
“We optimize our oils for specific applications, and during break-in you’re not going to be seeing higher temperatures and sludge. Synthetics are good oils for engines that have already been broken in, but they make it very difficult to get proper ring sealing,” he said.
A break-in oil is used for just that, breaking in a new engine. Although many new cars might have synthetic oil for a factory fill, Diehl stated that the reason that works is because factory engine builds are all based on specific and consistent tolerances. He said, “Most aftermarket engine builders are not going to spend that kind of time and money to get exacting tolerances, it would be too costly.” For example, they don’t use the same piston ring part number in all of their builds or the exact same block type for all their builds, which affects the consistency of the hone finish.
A break-in oil will be in the car for just 500 miles, and once ring seal has been achieved, then a synthetic can be used. Synthetics can run longer than a conventional oil between changes, but it doesn’t mean that a conventional oil isn’t going to perform in a hot rod or musclecar.
When it comes to racing oils, Diehl stated they should only be used in racing applications. He said, “Just because someone races a car a couple times a year, it doesn’t mean that they need to add racing oil. Racing oils are meant for those who might rebuild their engines every year or so.”
“We lower the detergents for racing oil because you’re not trying to go 5,000 miles,” Diehl continued. “Racing engines will reach a higher oil temperature and the oils are designed for more bearing film strength to help achieve longer part life. A street oil will have more detergents to help break down the sludge and varnish from driving several thousand miles.”
Racing engines will reach a higher oil temperature and the oils are designed for more bearing film strength to help achieve longer part life. A street oil will have more detergents to help break down the sludge and varnish from driving several thousand miles. -Scott Diehl
As long as the oil doesn’t show signs of darkening it can remain. Once the oil darkens, then it should be changed, as well as at proper intervals of up to 3,000 miles.
Diehl recommends a conventional oil for typical, low mileage driving where the car is seeing just a couple thousand miles each year, and being stored in winter. He says that there really isn’t an advantage to using synthetic, and the drawback is that it’s a little more expensive.
For vehicles that see more use, higher engine oil temperatures and colder climates, synthetic has a few advantages. First, the extended oil change intervals mean that it can stay in your engine longer. They can also help reduce oil temperatures by as much as 20 degrees, but that does depend on the application and how the engine is used.
According to Diehl, “Synthetic flows better at colder temperatures and they perform better at higher temperatures and tend to not thin out as much as conventional oil, thus providing a better film strength.”
Here we tried to show you why off-the-shelf additives might not be the best for your engine oil, and why certain additives need to be formulated with the oil, rather than just poured in. It’s also important to note that engine oils for modern cars may not be the best oils to add to your hot rod or musclecar. It’s tempting to just buy that five-gallon jug of 10W30 from the retail stores, but price should not be the deciding factor when it comes to protecting your engine.
Diehl was quick to add, “People who buy oil based on price are not doing their engine justice. It doesn’t make sense to put thousands into an engine and the last thing you put in – the oil – you buy what costs the least amount. Why spend extra money on H-beam rods and then put inexpensive oil in the crankcase?”
He states that engine oil is a very serious thing, and we should consider using better oils that were made with specific applications in mind, with the right additives based on use, not price. If you want to find out what engine oil is best for your application, reach out to the staff at Driven Racing Oils and let them help you choose. After all, Diehl says that’s what he does on a daily basis, and they look forward to your call.