Synthetic Motor Oil - Do Synthetic Oils Really Work?

Synthetic Oil May Make A Few Horses Under Extreme Conditions, But The Real Benefits Are On The Street Over The Long Haul...

Jeff Hartman Jan 1, 2002 0 Comment(s)
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Synthetic engine oil typically costs 2 to 4 times as much as conventional mineral oil, but it is definitely cheaper than an engine or a vehicle. The US military exclusively uses synthetic oil in all aircraft and the space shuttle. Aircraft manufacturers exclusively require synthetic oil in civilian jet turbine engines on airliners. GM sprung for synthetic oil in the LT1 Corvette when deletion of the C4's sump oil-cooler resulted in oil temperatures higher than The General liked with conventional mineral oil. GM mandated synthetic oil in the twin-turbo Calloway Corvette supercar with its Chevy-dealer warranty. When it really matters if an engine lives or dies under harsh conditions, synthetic oil is the way to go.

The question on most people's lips is "How much power will a performance engine gain with synthetic oil," when they should be asking, "How long will my engine last?"

Some dyno tests seem to indicate that changing to synthetic motor oil can actually add a few horsepower (see sidebar). But there are many ways of picking up a few horses. How many horsepower tricks make your engine more reliable?

We're planning to create a few "harsh conditions" of our own in the upcoming GMHTP Magnum TPI Firebird project. We'll be making some serious horsepower in the 396-inch Firebird, and we're so confident of the value of synthetics, we'll be using synthetic lubricants from Royal Purple everywhere from the crankcase to the rear axle. Our attitude is, when you're exploring the ragged-edge of street power, synthetic oil could make all the difference. When a big-buck engine is at stake, synthetics are actually dirt-cheap.

Synthetics are not controversial: "Synthetic oils do lubricate better," says AAA's web site. "If your vehicle is subject to extreme conditions such as sustained high speeds or high loads, extremely dusty conditions, racing, towing, use of a turbocharger, etc., the use of a conventional oil may not adequately protect your engine. If you are putting a lot of stress on your oil you might consider a change to synthetic oil and staying with a short change interval."

Exactly our plan with Magnum TPI.

Synthetics Oil: The BasicsSynthetics are not new. Synthetic engine oils were first mass-produced by the German chemical industry for the 1941-42 Nazi Blitzkrieg in Russia when petroleum was scarce and winter temperatures were so frigid that Panzer engines running ordinary crankcase oil had to be heated with an open flame under the oil pan prior to starting (or run almost continuously) to prevent the oil from congealing into a tar-like sludge that could prevent the engine from cranking (see History sidebar).

In the US, synthetics were designed for military tactical/combat fleets in wide-temperature operations. Mil-spec synthetic lubricants were successful and they have been used on military vehicles and aircraft (including the space shuttle) since the 1960s. Synthetic lubricants help Uncle Sam's engines survive cold starts under harsh low-temperature conditions with less wear. They help military engines survive long oil change intervals in combat conditions. In an emergency, they can enable engines to survive with critically low levels of coolant or crankcase oil.

The base stock for engine oils consists of medium-size hydrocarbon molecules in the range of 25-40 carbon molecules, which are not too thick or too thin and can be pumped under high pressure between moving metal surfaces of an engine to provide a slippery "thick film" that prevents metal-to-metal contact and all but eliminates friction. Conventional mineral oils are physically separated by distillation from the stew of various hydrocarbon molecules and impurities in crude oil. The end result is that mineral oils themselves consist of dozens of varied medium-weight hydrocarbons plus contaminants.

By contrast, synthetics are "designer" oils, chemically assembled or synthesized in labs from homogeneous low-weight molecules into heavier molecules with a chemical structure optimized for reduction of friction in specific applications. Synthetic oil molecules have a uniform size and chemical performance, resulting in an extremely stable product with highly predictable performance. Synthetics are entirely free of undesirable impurities like wax and ash. All synthetics are more expensive than conventional motor oils due to the complexity of the manufacturing process.

Synthetic oil manufacture begins with the production of pure ethylene gas from crude petroleum or natural gas. Ethylene is synthesized into homogenous light-weight hydrocarbons that are then polymerized to achieve thicker polyalphaolefin synthetic base stocks of heavier molecular weight. Synthetic base stocks also contain pure esters, which are essentially acid/alcohol compounds fully compatible with essential oil additives that are vital to the performance of modern motor oil in an automotive engine. Esters must be carefully blended with polyalphaolefins (which are thermally stable over a wide range but not particularly compatible with essential additives).

Specific measurable results from careful testing prove that synthetics are superior in the lab to conventional oils. Synthetics are clearly also great performers in the real driving environment. Unfortunately, it can be difficult or impossible to quantify the exact advantages of synthetic in a particular vehicle-especially on lightly-stressed stock factory engines in ordinary driving conditions where modern, high-quality mineral oils work quite well. It can be a little like a person trying to quantify the benefits of wearing sunscreen indoors.

Whether a synthetic lubricant will actually make a difference in the case of your engine all depends. How stressed are critical components on your engine such as crank bearings, rings, wrist pins, turbine bearings? How much thermal loading must your engine endure? How dangerous or expensive would it be if your engine failed catastrophically? In your case, synthetic could be overkill.

But do you really want to find out? In fact, the newest 100-percent synthetics have produced dramatic results in long-term-durability test engines, logging 200,000 miles with insignificant wear. Synthetic oils are so good that race engine builders are now virtually all using synthetics.

Why Synthetic Oils are BetterSynthetics are better both for what they contain and what they lack. They contain none of the traces of wax or ash of which conventional mineral oils cannot feasibly be 100 percent-free for economic reasons-impurities which accumulate on engine parts as the lighter fractions of mineral oil easily vaporize or are consumed in the combustion chamber, leaving thicker hydrocarbons and impurities behind.

With their tightly coherent molecular structure, synthetics also have inherently better resistance to thermal breakdown at high temperatures. Synthetic oils also flow better at particularly low temperatures (-60F vs. -40F). Synthetics typically require no pour-point depressants for cold starts and little or no VI-improver to maintain viscosity at high temperatures.

Whereas conventional oils begin to actively decompose into vapor and sludge at temperatures in the 340-450F range (which can happen in piston rings and turbocharger bearings), synthetics continue to lubricate critically hot parts without degrading. Synthetics are far more resistant to long-term breakdown and thickening via repeated "cooking" under heavy, hot loading over long intervals.

In the lab, synthetic performance advantages include wider-range viscosity index without VI improvers, lower ash content, higher flash point, lower boiling point, and lower pour (freezing) point.

Dollars And Sense: Why You Can't Afford Not To Use SyntheticsExperts will point out that synthetics can typically perform adequately for twice the typical recommended oil change intervals, as long as you replace the filter at specified intervals. But GMHTP recommends that performance enthusiasts think of synthetic oil as a kind of insurance policy which stays in force when you change it frequently. While it's true that fresh synthetic can maintain acceptable integrity for 25,000 miles or a full year of use in a healthy engine, we think that's a bit like buying expensive running shoes to protect your feet and joints-and then over-using them to the point at which they're no better than junk shoes.

No matter how good a synthetic oil may be when fresh, any engine oil will gradually accumulate combustion blow-by and other contaminants that cannot entirely be filtered out and thus gradually damage the oil. What's more, any synthetic oil can degrade more quickly if abused.

Even if you're using a top-quality synthetic, we recommend you follow vehicle manufacturers' recommendations for "Severe Duty" applications. Synthetic oil does cost more. But how much? Consider 24,000 miles of usage. Assume you change conventional API SJ mineral oil yourself every 3,000 miles (good insurance), and that your engine requires 5 quarts of oil at $1.50 each per change, and that the filter costs $3.50, plus tax, for a total of, say, $11.50. Over two years, you'll need 7 oil changes, for a grand total of about $80. Now assume you use $4.50/qt. synthetic-just to be sure. The seven oil changes now cost about $195-a difference of $115 you could think of as a sort of "catastrophic-illness insurance" which amounts to less than $5 a month over two years. Clearly, this is less expensive than the hundreds or thousands of dollars it costs to replace internal engine parts.

The Soul Of A Synthetic: AdditivesOil additives are expensive but vital to the performance of any modern engine oil. Manufacturers exercise extreme care in order to ensure that no mutually antagonistic effects occur between additives themselves or with the base lubricant. In addition to its primary thick-film lubrication function, oil must control engine deposits and keep foreign particulate matter in suspension that is too small to be filtered from the oil. Oil must also prevent corrosion and provide thin-film lubrication when hydrodynamic lubrication fails and metal-to-metal contact does occur. Anti-wear additives form an inorganic thin film between engine metal surfaces which shears more easily than the base metal, allowing parts to slide against each other without causing component failure. Such components typically do not work well in cold oil, which is one reason starting a cold engine causes a lot of wear. The anti-wear additives eventually get used up, one more reason oil must be changed periodically.

Seventy percent of lubrication-related friction is caused by oil film molecules rubbing against each other. The other 30 percent comes from parts protected by thin film lubrication rubbing against each other. Friction Modifier additives further smooth this contact, providing a small additional reduction of friction.

A vital task of a modern oil is to keep sludge, varnish, and carbon from clogging up the works of an engine. Manufacturers add detergents and dispersants (mineral oils require more to combat innate contaminants) to keep small bits of trash too small to be filtered out suspended so they circulate until the next oil change rather than "coagulating" on parts in deposits large enough to have an abrasive effect. If the detergents and dispersants wear out-or sufficient crud accumulates that the oil can no longer hold it, sludge and varnish will coat the internal surfaces of an engine in a hurry. All modern engine oils contain additives designed to prevent oxidation of the base stock, and to neutralize acids formed from oxidized oil or combustion blow-by gases. Thin-film additives also help protect bearing surfaces from corrosion.

The low-temperature flow characteristics of a thinner oil help avoid significant wear at startup time and increase fuel economy. But single-weight "winter" base stocks don't perform well when hot, so chemists created multi-viscosity oils using high-temp viscosity index (VI) improver additives. Synthetics typically do not require large amounts of VI additives (in some cases none) to achieve excellent high-temp performance.

Synthetic Horsepower on the DynojetWe drove two test vehicles to Dynojet chassis dynamometers at Winter Performance and Strope Speed where the professional tuners and dyno jockeys could help us scientifically evaluate the effect of synthetic engine oil on performance. Test Vehicle No. 1 was a bone-stock 2001 Camaro SS 6-speed, loaned to GMHTP from the Chevrolet press fleet. The vehicle had enough miles that the oil had been changed more than once. Test Vehicle No. 2 was our very own "Project Thunderchicken," a vastly-hotrodded LT1 Firebird whose stroker 396 powerplant had made slightly over 400 rwhp on the Dynojet 40,000 hard miles ago.

In order to compare apples to apples, we first dyno-tested each vehicle with the used oil that was in the sump. In the case of Thunderchicken, the vehicle was due for an oil change, so after the initial test, we changed to fresh Quaker State 10W-30, a high-quality conventional mineral oil which meets the latest API SJ standards, and tested again. Finally, we changed the oil in both vehicles to Royal Purple 10W-30, a synthetic motor oil which meets API-SJ standards donated to GMHTP by the manufacturer for testing. RP synthetic lubricants are marketed through performance dealers for racing and hotrod usage and through other channels for industrial usage. In each case, we did our best to make sure that temperatures of the engine, oil, and inlet air were not a factor in comparing the two oils' performance. In each case, we made several dyno pulls, but not nearly enough to be statistically significant to a 95-percent confidence, particularly given the miniscule changes in torque and the potential for tiny changes to be cancelled out by "dyno noise." We chose the best dyno pulls with each type of oil and compared them.

From 4400 rpms to 5800, the Camaro SS was up on both torque and power using synthetic, with the dyno registering peak power of 325.4 rear wheel horsepower (rwhp) with Royal Purple synthetic versus 320.8 rwhp with the slightly-used unknown-brand mineral oil. It should be noted that in this test, we did not change over to fresh mineral based oil to quantify the effects of new mineral oil.

Thunderchicken has been a mite tired lately in the higher revs (we suspect the valve springs are weakening a bit). In the first Thunderchicken pull, peak rear-wheel power stood at 388.9. With fresh Quaker State 10W-30, power increased to 392.3. When we changed to Royal Purple 10W-30 synthetic, power maxed at 393.3 rwhp. Peak torque went from 382.6 to 384.5, to 383.9 with the RP synthetic. Average rear-wheel torque over the range of 2200-6000 rpm changed from 368.63 to 367.34, average power from 288.3 to 287.4.

In the Thunderchicken test, there was a 0.6 lb.-ft. torque change out of 384 lbs.-ft.--about 1/6 of a percent difference. A change of one horsepower out of 393 is about a 1/4th of a percent. In fact, applying T-test statistical analysis to the 76 pairs of results for torque and power across the range from 2200 to 6000 rpm for the two types of oil, we find a very small likelihood that the oil change actually made a difference in power. In the case of the stock SS Camaro, 4.6 rwhp out of 321 is about 1.5-percent (which might alternatively have been achieved by a change of fresh mineral-based oil). Still nothing much to write home about. Conclusion: It takes harsher conditions than a few eight-second dyno pulls for synthetic oil to really shine at our intended purpose: making the engine live a long time under harsh conditions without wearing out or catastrophic failure. In our view, any extra horses are purely a bonus.-J.H.

The Functions Of An Engine LubricantLubricants function to reduce friction, remove heat, and contain contaminants.

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