Slippery Facts About Engine Oil

BY Jeff SmithPhotography BY THE AUTHOR

nless you are an oil geek and make it a habit of staying current on API specifications and what is happening in the ever-changing world of engine lubricants, it’s likely there are a few technical tidbits in this story that should be of interest to you regarding the oil you’re using in your performance street car engine.

Flat Tappet Break-In

It’s no secret that the world of engine oil is in a constant state of change. This has been going on for decades but a major shift occurred when the American Petroleum Institute (API) began removing the anti-wear additive zinc dialkyl-dithiophosphate (ZDDP—don’t worry we won’t ask you to spell it) from engine oil throughout the mid ’90s onward. This occurred because new car manufacturers requested the ZDDP levels be lowered because when that additive is oxidized during combustion, it produces an ash that tends to poison catalytic converters.

API testing showed that these reduced levels of ZDDP did not significantly increase engine wear because most all production engines by the mid ’90s employed roller tappets. However, when performance engine builders used this same oil for their flat tappet camshaft engines, that’s when the troubles began.

The most pronounced issue occurred with breaking in these flat tappet camshafts. Most everyone knows now that they must use a quality break-in oil like AMSOIL’s specialty break-in oil that employs a higher ZDDP content intended to offer sufficient protection for the initial wear-in period.

Diesel Oil

Many enthusiasts expound on the advantages of using diesel engine oil containing high ZDDP, anti-wear capability, and detergency in their performance engines. While diesel oil remains a solid option for some performance engines, specialty oils have come to the forefront with higher levels of ZDDP that can perform these tasks much better. The market offers multiple engine oils that can perform this function, such as AMSOIL’s Z-Rod as a synthetic, Driven’s various performance hot rod oils, and Comp’s high-ZDDP oils that can do the job much better than the diesel lubricants.

Specialty Oil

What many enthusiasts fail to recognize is that once their flat tappet camshaft and lifters are properly seasoned, that specialty “hot rod” oil with higher ZDDP levels is needed in order to allow the cam and lifters to survive. The most common mistake is that regular off-the-shelf API SN/SP oil is used in these flat tappet camshaft engines after break-in. The end user might be thinking his engine is OK since it appears to run fine, but the reality is that the camshaft and lifters are slowly failing.

To prevent this eventual failure, it’s best to use a properly formulated “hot rod” oil, of which there are many. Among them are several from companies like AMSOIL’s Z-Rod, Driven Racing’s selections, along with others such as Comp’s oil in 10W-30, 10W-40, and 20W-50 viscosities. These oils are often more expensive than regular API-spec oil but certainly worth it when it extends engine life. Furthermore, the AMSOIL Z-Rod is a full synthetic compared to conventional oil for the other brands.

Synthetic Oil

Having mentioned that AMSOIL is synthetic, this seems like a good place to detail what is in a typical quart of oil, either conventional or synthetic. All engine oils consist of two parts: a base oil and an additive package. Think of engine oil as being like lemonade, which consists of water as the base and the lemon juice and sugar as the additive package.

Among the factors that affect the selection of a good high-performance engine lubricant is the question of conventional versus synthetic oil. As a quick definition, conventional oil is minimally refined from crude oil extracted from the ground. Synthetic base oil is engineered for performance, including improved physical and oxidative properties.

Synthetic base oil offers substantial protection improvements over conventional oil that can offer some interesting opportunities for performance engines. Our friend and oil engineer Lake Speed Jr. performed a test several years ago abusing a 383ci small-block Chevy on the dyno to test a synthetic against a conventional oil with the same additive package. The test abused the small-block at under 4,000 rpm, wide-open throttle (WOT) conditions at oil temperatures above 250 degrees F. The test revealed substantial and visually impressive bearing wear on rod and main bearings using conventional oil while the synthetic oil of the same viscosity revealed much less wear. An independent testing house performed a similar test using AMSOIL 100 percent synthetic 5W-30 oil simulating 100,000 miles worth of wear and found similar results. These tests fully reinforce the concept that synthetic oil can radically reduce engine wear and extend engine life.

Synthetic Blends

This brings us to the next point involving synthetic blends. This is a common technique used in the petroleum industry. When a company lists a synthetic blend on the label, there is no industry standard for the amount of synthetic base oil used. It could be 50 percent or less than 5 percent. AMSOIL has a line of synthetic blend products as well but clearly states they contain more than 50 percent synthetic base oil.

There are performance advantages to using a synthetic blend oil, but it’s near impossible to determine the percentages since the various manufacturers prefer not to discuss this on the packaging. Generally, this is because the percentages are very low.

Other major advantages of a synthetic base oil is that its high and low temperature performance and oxidative stability. This stability can lead to improved deposit prevention, which reduces sludge buildup. A common misconception is that oil “wears out.” The proper explanation as to why engine oil eventually needs changing is because the additive package is depleted.

Extended Range

This leads us to an additional category called extended drain interval oils. These can be either conventional, semi-synthetic, or full-synthetic versions. As mentioned earlier, base oil does not wear out but the additive package does deplete over time. Extended mileage oils merely increase the percentage of additives in the oil which increases the miles driven in between changes.

As an example, AMSOIL offers a Signature Series synthetic in which AMSOIL increases the drain interval to 25,000 miles, one year, or 700 hours of operating time. A major advantage to synthetic base oil has the ability to exceed industry standards for performance characteristics. By using high-quality synthetic base oil, the AMSOIL Signature Series offers the opportunity to extend the drain interval. This may not necessarily appeal to a performance engine enthusiast, but the opportunity to use higher quality oil is certainly an advantage even if you don’t use it to its fullest capacity.

Viscosity

One of the more important questions that many enthusiasts ask is what viscosity should they run for their high-performance small- or big-block engine? This is a somewhat complex question that is beyond the scope of this story because of all the details that should be covered in order to answer the question correctly.

It’s best to first detail what the numbers mean. Viscosity is the reference to how well oil will flow at a certain temperature. The first number in multi-viscosity oil like 10W-30 refers to the viscosity rating of the oil when laboratory tested at a cold temperature of -13 degrees F based on the ASTM D5293 cold-cranking test. The “W” does not refer to “weight” but instead references “Winter” for the first number. A smaller number first like 5W-30 would indicate that the oil would flow more freely at cold temperature than a 10W-30.

It’s important to note that any oil will thin as the temperature increases. The goal for any oil is to maintain as much film protection as possible to prevent the crankshaft journal from contacting its bearing surface. This becomes difficult as the temperature increases and the oil becomes thin. Synthetic base oils offer more stability but will still thin out with temperature.

The second number indicates the viscosity of the oil when tested at 212 degrees F (100 degrees C) using the ASTM D445 standard. It’s common that any oil will lose viscosity when exposed to higher temperatures. To protect the engine, thicker oil with a higher viscosity is generally used when the engine runs at higher operating temperatures. A larger number indicates that when the oil thins it will still provide the protection needed at this higher temperature. However, going too thick can lead to oil starvation and a lack of lubrication.

Multi-viscosity oils use a complex combination of base oils and additives like viscosity modifiers designed to provide the desired viscosity range. Both base oils and viscosity modifiers have the ability to flex throughout the band of operating temperatures but its viscosity ranges are significant in multi-grade products like a 0W-40 or 5W-50. Viscosity modifiers have the ability to shrink in cooler temperatures, allowing for faster flow and then can expand when exposed to hotter temperatures to provide the optimal viscosity across the full operating temperature range. This produces oil that can flow properly at very low temperatures while still able to protect the engine when oil temperatures reach beyond 200 degrees F.

Assuming an older engine like a small-block Chevy is a normally aspirated street engine running normal bearing clearances, you will not go wrong using 10W-30 or 10W-40 viscosity oil. Older engines from the muscle car era, like FE Fords, use a 2.75-inch main journal while Oldsmobile engines, for example, used even larger 3.00-inch crankshaft main journals. This added girth demands larger clearances and therefore thicker viscosity oil like a 10W-40 or even a 20W-50 to maintain proper oil pressure and bearing protection.

The major influencers for choosing a specific viscosity oil are a combination of bearing clearance and operating temperature. A drag racing engine that does not see high oil temperatures could use a thinner oil compared to an endurance engine that sees operating temperatures of 250 degrees F or higher. The endurance engine would be better suited to a higher viscosity oil to better handle the greater thermal demands on the lubricant.

Since clean oil is better than dirty oil, filters are a necessary part of any engine application. One question that occurs from time to time is the use of reusable mesh filters. They may claim to filter down to let’s say 20 microns, but the key to filter performance evaluation is the efficiency number. Most quality filters like an AMSOIL, Fram, or Wix will offer efficiency numbers that will tell you how well the filter removes dirt. For example, AMSOIL’s filter is capable of 99 percent efficiency at removing dirt as small as 20 microns. A micron is one millionth of a meter or 0.000039 inch. This means that all but 1 percent of all 10 micron or larger debris will be filtered out of the oil. Since that dirt is much smaller than the bearing clearances, the engine should be well protected.

The issue with reusable filters is that if they claim trapping a 10-micron piece of dirt, they will not claim an efficiency number even close to what these paper filters can deliver. So, the smart option is to use a good paper filter and avoid the fancy, reusable ones. Plus, consider the dirty solvent you will be immersing that reusable filter in while it is being “cleaned.” This step might actually make the filter dirtier than it was when installed in the engine.

There’s far more to the subject of high-performance lubrication than we’ve touched on here but this should give you a solid knowledge base from which to make your next oil decisions. It’s a slippery subject, but one that we geek out on from time to time!

1. Using a quality break-in oil like one of these three will offer the best opportunity for flat tappet cams and lifters to survive the initial run-in time. There are many more details that need to be addressed to be truly successful, but it starts with a quality break-in oil with sufficient ZDDP levels.

3. Be cognizant of the fact that a synthetic blend could contain either a large or very small amount of synthetic base stock and still be called a blend. This does not make a blend a bad choice but be aware that the percentage of blended synthetic stock is a variable because there is no industry standard for the percentage of synthetic base stock used.

4. Choosing the correct viscosity for a stock production engine is easy—just use what the manufacturer designates. But for a custom-built performance engine, you might want to refer to this chart found on Driven’s website that offers recommendations based on oil temperature, clearances, block, and connecting rod material.

6. In an interview with a Fram filter engineer several years ago, his quote was, “The best oil filter in the world is a really efficient air filter.” This makes perfect sense since the engine ingests millions of pounds of air over its lifespan. The cleaner the air going in the engine means the cleaner the oil will be over its lifespan. This should make you think carefully about using a fully sealed air cleaner combined with a good PCV system.

8. Our friend Lake Speed Jr. did a test a few years back comparing synthetic against traditional oil of the same viscosity using a 383ci small-block Chevy under high load at a very low engine speed to increase the load on the bearings. The test revealed that synthetics do a superior job of reducing wear. The bearings shown here were from the conventional oil test while the bearings used with synthetics appeared near new. Another test showed that coated engine bearings performed even better when combined with synthetic oil.

10. The item to study is not only the size of the dirt that a filter can trap but also the filter’s efficiency. AMSOIL filters are rated at 99 percent efficiency at removing dirt and debris 20 microns and larger and can capture dirt as small as 2 microns yet still offer sufficient oil flow to not overly restrict the lubrication system.