Engine Oil - A Slippery Subject

Of all the advanced technologies that have impacted the automobile, some of the most significant, and perhaps the most seldom recognized, are the advancements in lubricants. And while modern engines, like all the other components cars contain, have become more refined, much of the mechanical longevity we enjoy from our vehicles today can be traced to the oils we generally take for granted.

As with most products on store shelves, marketing plays a huge roll in selling oil. There are big ad campaigns and colorful bottles with all sorts of claims, slogans, and phrases to influence your decision-making process. Even so, the process is fairly straightforward when it comes to selecting the right stuff to pour in the crankcase of a contemporary car. Simply following the manufacturer's warranty recommendations for grade and viscosity, regardless of the brand name on the container, is about all there is to it. There's even a little book in the glovebox that tells you how often whatever brand oil you choose should be changed. But street rods don't usually come with an owner's manual, and making blanket recommendations for oil, especially since one rod may be powered by a Flathead Ford and another by an LS1 Chevrolet, isn't practical, or prudent. In addition, there are differences in engine oil that go beyond the hype on the container. Our intent here is to give you the information you need to pick the oil that's best for your street rod.

API StandardsThe American Petroleum Institute is the main U.S. trade association for the oil and natural gas industry. Among the many functions of this organization is the administration of a system that identifies the two general classifications of oil.

API's service code appears on oil packaging and is often referred to as the donut. Broken into three parts, the top portion is a series of letters used to identify the application and performance level the oil has been tested at and achieved. The first letter in that code is either an S for service, and refers to passenger cars and light trucks, or C for commercial applications or Diesel engines.

Next in both cases is a letter that refers to the most current test standards the oil has met. As an example, API's newest service designation is SM for gasoline engines; M refers to the latest laboratory and engine tests that include control of high-temperature deposits. Currently, API service categories for gasoline engines include SM, SL, and SJ. At present, there are six Diesel engine categories-CI-4, CH-4, CG-4, CF-4, CF-2, and CF (the 2 refers to two-stroke Diesels, the 4 to four-strokes). Keep in mind, it is possible for an oil to conform to both the gasoline and Diesel standards, so both S and C categories may appear on the same container. Another organization that develops standards for oil is the International Lubricant Standardization and Approval Committee (ILSAC). Their latest standard is GF-4.

In the center of the API donut are the numbers that identify the oil's viscosity, or thickness. Established by the SAE, or the Society of Automotive Engineers, the higher the number the thicker the oil. Oil's viscosity is normally defined by the time required for it to flow through a standard-size orifice; the longer it takes the higher the SAE number. However, one of the things that complicates the issue is that oil gets thicker when it gets cold and thinner when it gets hot. For that reason, oil viscosity testing is done at established temperatures-212 and 32 degrees Fahrenheit.

Some oils are tested at just one temperature, single-grade motor oil is just that. SAE 30-weight motor oil is tested at 212 degrees; it gets thinner when it gets hotter and thicker when it gets cooler. That's why it was once common in some parts of the country to change the viscosity of an engine's oil with the season. It wasn't unusual to run 20-weight in the winter and 30- or 40-weight in the summer in places where temperatures varied dramatically.

The introduction of multi-grades is one of the technological advancements in engine oil that has made selecting the proper oil viscosity easier. These products use viscosity modifiers that allow it to flow like lightweight oil when cold, and heavier oil when hot. As an example, a 10W-40 oil (the W stands for winter in multi-grades) flows like 10-weight at 32 degrees and 40-weight at 212 degrees. The advantage to this is that the oil is thin enough at low temperatures to allow the engine to crank easily and for the oil to flow where it needs to be, yet the oil is thick enough to provide the necessary protection of the moving parts when the engine gets warm.

Mineral Versus SyntheticWith apologies to fans of spaghetti Westerns in general, and those of Eli Wallach in particular, there are two kinds of engine oil in the world, my friend-mineral and synthetic. Conventional contemporary motor oil contains roughly 80 to 95 percent petroleum base stock that has been refined to remove impurities; the remainder is made up of various additive packages that are put in the mix to make the oil suitable for its intended use.

Synthetic motor oil is made of synthetic hydrocarbons. And while the claim to be "fully synthetic" is a common one, most of these products actually contain a 70 to 85 percent synthetic base with the remainder comprised of a variety of additives including zinc, boron, calcium, phosphorus, magnesium, etc. And while these additives aren't synthetic, it is permissible for them to be advertised as fully synthetic due to API standards concerning the makeup of the base stock.

Synthetic oil has actually been around for quite some time, with the earliest attempts at production being made prior to 1900. The next big push in research was a result of Germany's oil shortage during World War II. It prompted intense investigation into the possibilities of creating synthetic lubricants. In fact, from 1944 on, 10 percent of the oil produced in that country was synthetic. However, it was the needs of jet engines that ushered in the new era of synthetics; long duration, high-speed operation, as well as huge variations in operating temperatures demanded performance beyond the scope of conventional oils. Synthetic oil was the answer to that need.

An interesting variation that is somewhat new on the scene is synthetic-blend oils. These are a combination of a mineral oil base and no more than 30 percent synthetic oil. They are designed to provide many of the benefits of synthetic oil at a price point in between mineral oil and pure synthetic.

To add even more variety, or perhaps more confusion, when it comes to selecting engine lubricants are the new labels declaring them to be formulated for a specific application. The additive packages that have been tweaked for a specific purpose make them different. As an example, high-mileage oil contains additional conditioners to keep engine seals pliable. It is also formulated to resist vaporizing, or burning, in the combustion chambers, that helps reduce oil consumption in some engines.

The Vintage Engine IssueThe question of the appropriate oil looms large for lovers of antique iron.

As most of us are aware, new cars use much lower-viscosity oil than what was common in the past. Increased gas mileage is certainly a factor in that decision, but newer engines also have redesigned oil pumps and galleys as well as high-tech materials and tighter clearances to allow the use of lower-viscosity oil. And while older engines can certainly benefit from the higher-quality oils that are on the market, the very low-viscosity oils are probably not the best choice (see the FAQs for more on this).

What's Right For Your Rod?In the process of gathering information for this story, we asked questions of a number of highly qualified individuals including: Kelly Tidwell, vice president and co-founder of Pure Power! Incorporated, in charge of research and development of new products, laboratory and field-testing, quality assurance, and industry standards and regulations; Mark Ferner, Quaker State's team leader for the company's research and development program; Matthew Ansari, Chevron's global technology manager for PCMO (passenger car motor oil); Ed Newman, marketing and advertising manager for Amsoil; and Cameron Evans, director of sales and marketing for the Red Line Synthetic Oil Corporation (and former editor of Popular Hot Rodding). Not surprisingly, there are some differences in opinion on some points.

Our ConclusionsWhen it comes to choosing oil, we are confident in saying any of the mineral-based oils on the market that meet current API specifications are more than adequate to protect the engines in the majority of street rods. We say "the majority" only because we know there's someone out there somewhere running a nitro-burning Hemi or a gas turbine in their daily driver that may have some special needs. But, a quality mineral oil will provide the protection necessary if your rod is powered by anything from a contemporary crate engine to a modified motor that is still capable of operating in a street environment.

So, does that mean we don't recommend synthetics? No, it does not. We believe synthetic oil does have advantages, such as increased protection at extremely high engine temperatures (above 230 degrees), better flow characteristics at low temperatures, and that it can reduce wear and friction in many instances. The down side to synthetics is that they are more expensive, but then the recommended drain interval is longer, so price may be a moot point if you put lots of miles on your car between oil changes. So, the obvious question you have to ask yourself is, "Does the engine in my street rod require what synthetics have to offer for the difference in price?" For some the answer is no, while the peace of mind may be worth the investment for others.

When it comes to selecting engine oil, consumers have a variety of products from which to choose. And for the same reasons some people buy Fords while others choose Chevys, Mopars, or Toyotas, the decision on which oil to use may be made on the basis of who has the most effective ad campaign, recommendations from friends, or personal experience. Fortunately, as a result of today's competitive business environment and manufacturer's warranty requirements, as well as the constant scrutiny of organizations like the API and ILSAC, we can't help but believe there are no really bad oils on the market. The trick is to pick one that will provide your street rod's engine with the protection it needs and you with confidence in your choice; hopefully we've helped with both.

FAQs About Engine Oil We asked our experts a variety of questions about engine oil, and here is what they had to say:

SRM: We've read that the amount of zinc has been reduced in engine oil. What does zinc do and will the reduction do any harm to older engines?

Mark Ferner: Zinc is used as an anti-wear agent; however, when oil gets into the combustion chamber, that zinc additive turns into an ash that can affect the operation of the oxygen sensor and the catalytic converter. The amount of zinc has been reduced to maintain emissions warranty requirements.

Matthew Ansari: Although zinc has been reduced, other effective anti-wear compounds are being substituted, although they are more expensive.

Ed Newman: Lowering zinc was of particular concern for flat-tappet/camshaft engines among automobile manufacturers and oil formulators prior to it being implemented. Certain engine sequence tests used to qualify previous oils when flat tappets are still used, which helps to demonstrate that lower-level zinc oils do not compromise wear protection. The end result is supplemental anti-wear technology and friction modifiers used in these formulations to compensate for reduced levels of zinc. Older engines of a stock configuration using low zinc formulations work perfectly. For modified engines with greater valve spring pressure, it is advisable to use oil with higher levels of anti-wear additives, such as zinc and phosphorus. By doing this, you help to ensure the life of your flat-tappet/camshaft system.

Cameron Evans: It is actually a combination of zinc, phosphorus, and sulfur that has been reduced in these API oils, with common off-the-shelf oils usually blended levels now half of what they did have. Zinc specifically helps in valvetrain anti-wear and piston ring wear (on the top ring where it shows signs of changing direction).

SRM: Should racing oil be used on the street?

Mark Ferner: Pure racing oil does not have the additive package necessary to meet warranty requirements. In racing applications, the oil is changed quite often, so an API-certified oil is a better choice for street engines.

Matthew Ansari: We have never done any testing in this area, but racing oil lacks many of the additives that are necessary for an engine that sees everyday use.

Kelly Tidwell: Racing oil is a unique subject. One would expect a racing oil to contain extra amounts of anti-wear agents, extreme-pressure agents, anti-foam agents, and so on, but this is not always the case. I have had analysis performed on a popular 20W-50 racing oil and the same analysis on their regular 20W-50, which actually had a higher zinc count than their racing oil.

Ed Newman: There are different types of "racing" engine oils. One type is used exclusively for racing engines only where the engines are torn down frequently and rebuilt and where the oil is only intended for use during one race. These oils, oftentimes, do not contain extra additives needed for general street use. They are essentially stripped-down versions containing only the needed components to protect the engine during the race.

More common are street-type racing oils that are beefed-up versions of everyday engine oil. They come in a wide variety of formulation designs. Some have higher viscosity grades, such as SAE 20W-50 or SAE 60, for better protection or to combat fuel dilution while others may be low viscosity, such as SAE 5W-30, for greater power and efficiency. These oils generally contain all the essential additives along with enhancements for improved film strength, for example.

Street-type racing oils are excellent for use in hot rods, musclecars, and trucks where the engines have been modified for higher horsepower. They will provide better protection than regular motor oil given the same viscosity. The street engine guy needs to select the proper oil depending on what he wants to achieve.

Cameron Evans: Racing oils should never be run in a street engine. Our 30WT Race oil (which is a 10W-30 multi-grade that carries that name in regard to its viscosity at its usual operating temp) differs from our 10W-30 motor oil mostly via a lack of detergent. Racers change their oil much more often and are looking for maximum lubricity, so the detergents that add to engine cleanliness and keep contaminants in suspension are left out for the most part. Our 10W30, 10W40, and 20W-50 motor oils that are popular with the V-8 performance crowd are much better and more convenient for the majority of enthusiasts.

SRM: What determines the oil viscosity an engine requires? Do vintage engines have any special concerns in that regard?

Mark Ferner: While thinner oil increases flow and frees up horsepower in newer engines, they are designed for it. In older engines, thicker viscosity is a safer way to go, as it will provide higher oil pressure and better ring sealing. However, there is no advantage to straight grade oil in vintage engines. Multi-grade flows better at start-up and thins less with heat; 20W-50 is a good choice.

Matthew Ansari: We, of course, recommend following the manufacturer's warranty requirements. However, in general terms, 10W-30 is a good choice for '85-and-newer engines with tight clearances. For older engines, 20W-50 is appropriate.

Kelly Tidwell: Some vintage engines should have higher-viscosity motor oil just because of the design of the oiling system.

Ed Newman: For gasoline engines, 10W-30 or 10W-40 are the most commonly used viscosities and will apply to practically all applications.

For many years, 10W-40 was the most common viscosity grade. The need for higher-viscosity oil arose from, in part, manufacturing technology of the time, causing loose engine tolerances, and engine oil quality was low compared to modern standards. Thicker oils will help to reduce oil consumption, wear, and to keep the oil pressure higher. These features are of particular importance in worn engines. If the vintage engine has had a high-quality rebuild performed and it is not modified for greater power, there is little need for thicker oils. Using 10W-30, for example, is fine.

Cameron Evans: More viscosity can certainly help for a true "vintage" engine with very wide clearances and oil pressure issues. However, we find that many street rodders commonly select an oil viscosity that is too heavy. Unless one is looking at .005-inch clearances or very worn rings, a 20W-50 is probably not required. Running such a heavy product usually leads to excessive wear at cold temperatures and gives up fuel economy. In many cases, it is possible to move down one oil weight (from 20W-50 to 10W-40) when switching to a fully synthetic product. The rule of thumb is to start with 10W-30 motor oil for crate engines, homebuilt engine projects, and the like. In a hot climate, 10W-40 is a better idea, and 20W-50 motor oil is only necessary in extreme conditions or very powerful engines.

SRM: What oil change interval and precautions are recommended for cars like street rods that may be stored for extended periods?

Mark Ferner: For engines that see restricted use, the oil should be changed every three months, otherwise water and unburned fuel can accumulate and produce "soft sludge." The best way to protect an engine is to change the oil before the car goes into storage, and then change it again before putting it into use. Even though the engine hasn't been run, water vapor will accumulate.

Matthew Ansari: Oil change intervals are a function of the car's use. Oil should be changed more frequently under severe conditions. Long storage periods, or any situation that keeps the oil from getting to a minimum of 180 degrees to burn off contaminants, is considered to be severe conditions; consequently, the oil should be changed more frequently.

Ed Newman: For best protection, install new engine oil, preferably with anti-rust properties, and run the engine up to operating temperature prior to storage. This ensures contaminants are not in the oil, which can cause corrosion, and that new oil has been circulated throughout the engine. Also, use a good-quality engine fogging oil that contains rust inhibitors and spray down into the carburetor while running to coat the intake system and valves. Next, spray into the spark plug holes to coat the inside of the cylinder. Turn over the engine a couple of times. Make sure to disconnect the ignition first.

Cameron Evans: Since drain intervals are determined by how you drive, an oil company would be irresponsible to provide customers with an exact figure. Cold oil shears or wears out faster than warm oil, so motorists who let their engines warm up more than others can go longer between changes. The same goes for long trips over short trips. If you're the kind of guy who logs a lot of miles, you can go far longer between oil changes than a fairgrounds cruiser who starts the engine, pulls it into gear, and drives very short distances.

SRM: It has been claimed that synthetic oils should not be used in vintage engines, primarily due to the types of seals and gasket technology they use. What is your opinion?

Mark Ferner: Due to the detergents, synthetic oil may clean deposits out of bad seals and cause leaks, but there is no reason synthetics won't work if the seals and gaskets are in good shape.

Matthew Ansari: The oil used has to be compatible with the seals used; in some cases, vintage cars may not tolerate synthetic lubricants.

Kelly Tidwell: There is general acceptance among mechanics that synthetics can create a compromising situation with older seals such as rope type.

Ed Newman: Properly formulated synthetic engine oils will not harm or damage rope seals or gasket material any more than a petroleum-based oil provided they are in good condition. If a rope seal is deteriorated, hardened, or damaged, it will leak regardless of the type of oil used. It is important to note that rope seals are not elastic and small changes or imperfections will increase their likelihood of leaking. As for gasket material, synthetic oils have to go through the same seal compatibility testing as petroleum oils.

Cameron Evans: Early synthetic products justifiably got a bad rap for causing leaks, but that is no longer the case, especially for an ester oil like Red Line that promotes seal swell. Older petroleum oils were really good at swelling seals, but PAO-based synthetics cannot do it as well as esters. Synthetic oils do a great job of cleaning up inside an engine, transmission, or differential. Many of the leaks attributed to synthetics come from the fluid's ability to pull the sludge and accumulation up and into suspension, revealing a gasket that likely needed to be replaced or a seal that has hardened and failed over time. An engine built with modern seals should not have any seal issues.

SRM: What are the pros and cons of mineral-based synthetic blends and full synthetic oils?

Mark Ferner: Quality petroleum-based oils meet manufacturer's warranty requirements and do so affordably and are appropriate for engines that operate at temperatures up to 230 degrees. Synthetics provide protection at higher engine temperatures (230-240 degrees), but they cost more. Blends split the difference between price and protection.

Matthew Ansari: Quality mineral-based oils that meet manufacturer's warranty requirements offer performance and durability at affordable prices. While synthetic oils may offer additional engine protection when extreme temperatures are involved (high engine-operating temperatures or in extremely cold climates) and extended drain intervals, they cost more. Blends fit in between in both price and protection.

Kelly Tidwell: Until zinc, boron, calcium, phosphorus, magnesium, etc., is either removed from engine oil or synthetically compounded, there cannot be a "full" synthetic motor oil. The buying public would be surprised at the amount of actual "synthetic" is in a synthetic oil. While the needs of a jet engine may require synthetic oil, a quality mineral-based product with the correct additive package will meet all the lubrication requirements any automotive engine requires.

Ed Newman: Mineral/petroleum oil: low-cost, readily available, moderate chemical and physical stability, poor cold-temperature properties, low heat resistance, medium deposit forming tendencies. Synthetic blends: moderate cost, improved chemical and physical stability, improved hot- and cold-temperature properties, longer life expectancy, reduced deposits. Full synthetics: highest cost, best chemical and physical stability, best hot- and cold-temperature properties, longest lasting, lowest deposit-forming tendencies, improved heat reduction, low coefficient of friction, reduced wear, improved mpg.

Cameron Evans: Most of the issue here is cost. Some consumers aren't comfortable spending as much as $10 per quart on motor oil. Petroleum oils are a cheap purchase and their offshoot synthetic blends offer a compromise of drain interval, wear protection, and cost. Regardless, we find that many of our customers would rather invest in the oil, change it less, and protect their investment.