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Go to a car parts place and you're sure to find lubricants like Castrol Syntec Blend. It is 25 percent synthetic oil, 75 percent mineral oil. The major advantage is it makes the oil slicker, which gives you better fuel economy and longer engine life. Unfortunately, synthetic blends have the same change interval as mineral oils do.
Following is Jim's Aperiodic Posting Explaining Everything He Knows About Motor Oil. Follow its recommendations at your own risk.
1. MOTOR OIL is a liquid lubricant designed to keep the pieces of your engine from touching each other. Many of these parts are separated by a film of oil two or three molecules thick, so this product is very important to your health and well-being.
2. There are three kinds of motor oil: Castor Oil, Mineral Oil and Synthetic Oil.
3. CASTOR OIL was discovered to be a very good motor oil during World War II. The allies needed a substitute for mineral oil because all the crude oil, which mineral oil is made from, was being turned into motor fuel. They tried castor oil, which is made by pressing the beans of the Castor Bean Plant, and discovered that not only does it keep the engine from sticking together, it bears the unique property of getting thicker when it's heated. Very important when you're running it in an airplane engine. We've turned away from this oil because it's too expensive and it doesn't last as long in the engine.
4. MINERAL OIL is made by refining petroleum. There's a bunch of stuff you need to know, so listen close:
a. The first thing you need to know is, what's the viscosity? IOW, how thick is the oil? There is a tradeoff here: if the oil's too thick, you'll waste energy pushing the engine through it; too thin, and the film of oil coating all your engine's parts can collapse, allowing the moving pieces of your engine to touch. (This would be bad.) The thicknesses, or viscosities, are rated using a scale developed by the Society of Automotive Engineers--SAE. The ratings go from zero to way in fuck up there--IIRC 150 is the thickest oil I have ever seen, although I've never seen battleship gearbox oil. Motor oils run from SAE 0 to SAE 50; everything else is called gear oil and you'll see it in manual transmissions, rear-ends on rear-wheel-drive cars, and the like. Generally speaking, new cars want to see an SAE 30 oil, new trucks want an SAE 40 oil and motorcycles want SAE 50.
aa. So what's this "10W30" shit? Glad you asked. This is a "multigrade" oil made for year-round use. It has two ratings. The first is the arctic, or "winter" rating and it's marked with the W. That W doesn't mean "weight." The other is the summer rating. These are measured with a tool called a Saybolt Viscosimeter--essentially a bucket with a hole in the bottom of it. There is one for the summer rating and a different one with a bigger hole for the arctic rating. To test the summer rating of the oil, cover the hole. Heat two ounces of oil to 212 degrees F and put it in the viscosimeter. Unplug the hole and time how long it takes for all the oil to run out, then compare it to the SAE table of viscosities. If SAE 40 oil is supposed to take between 100 and 120 seconds to clear the viscosimeter and this batch takes 115, guess what you've got. To check the oil's arctic rating, chill it to 0 degrees F and test it. (Now you know why the hole's bigger.)
ab. It gets even more fun: If you were to take just plain old unadulterated mineral oil that was capable of moving at all at 0 degrees F and heat it to 212 degrees F, it would be even thinner than water. (This is possible.) To get the oil thin enough to move at 0 but thick enough to keep the engine from collapsing in upon itself two minutes after you started it, we use viscosity improvers--complex polymers that shrivel up when they're cold and expand when they're hot.
ac. Europe used to rate their oil in Saybolt Universal Seconds--the number of seconds it took for two ounces of oil to clear the viscosimeter. Today European oils are all rated in SAE for two reasons--the automakers like it better, and the oilmakers can sell oil made for Europe in the US without replacing the labels.
ad. You'll see "HD" or "Heavy Duty" oils on the shelves. They're always single-grade. The viscosity modifiers shear off under heavy load, which keeps them from working properly. HD oil doesn't have them, so it performs better under lots of stress. If you use HD oil, watch the temperature chart and be willing to change oil grades two or three times a year.
b. Next is the API Service Rating. There are two--S and C. S ratings are for gasoline engines, and they run from SA to SM. SA oil is pure, unadulterated mineral oil. I buy this for my oil squirt can because it's really cheap and works okay for that. Don't put it in an engine. Don't even put it in your lawn mower. The two ratings you should care about are SF and SM. If you've got a car made before 1988, SF oil is just dandy and will save you some money. SM oil is more expensive to make because the additive package--detergents, viscosity modifiers, volatility modifiers--is more expensive. (The big one is the volatility modifier package. Someone at one of the big engineering schools discovered that by changing the way oil offgasses VOCs, you can change the amount of pollution in the atmosphere. They started using volatility modifiers at API Service SL and it's continued in Service SM.) There was no API SI or SK, and the ratings are upgraded every three years.
ba. API "C" ratings are for diesels. The top rating is CI-4 Plus for the next few months, but API CJ has been published. Not all S-rated oil carries a C rating--Castrol is famous for not supporting diesels. Every C-rated oil carries an S rating because an oil that works in a diesel will by default work in a gas engine. There are two kinds of oils that carry API C ratings. One of them is basically a gas-engine oil that will pass the C ratings, and you'll see something like API SM/CG on that oil. The other is specifically engineered to be a diesel engine oil. Here the ratings are far more complex. They'll start with the C-ratings, and generally they'll start with the highest rating and work backward. (If you've got an engine that costs $12,000 to rebuild and the manual says "use API Service CG oil" you are damn sure going to put an oil that passed the API CG tests in the engine. So, this stuff is tested for multiple ratings.) They then list the API S ratings the oil meets--this is important because a fleet operator buys motor oil in 55-gallon drums and puts the same oil in every vehicle the company owns. And finally, each engine builder tests and approves oils for its engines. So far, Caterpillar does not approve of synthetic oil in its engines and will deny warranty claims if it's in there. Even though synthetics are even better in a big engine than in a small one, the two favorite heavy-duty diesel oils are Shell Rotella T and Chevron Delo 400. These guys KNOW what those oils do. (Oh yeah: if you've got an aircooled Volkswagen run nothing but Shell Rotella T 15W40 in it.)
bc. Outside of the United States, the International Lubricant Standardization and Approval Committee, or ILSAC, tests oil. ILSAC GF-3 is the current rating.
c. There's also an "Energy Conserving" label on some oils. This one people are kinda glib about...the oil is supposedly slicker, which makes the engine require less fuel to run. I've gone through lots of oils, and it seems that the Energy Conserving ones are all something-W-30 oils. If you've got a vehicle that can take 30-weight oil, why not?
5. SYNTHETIC OIL falls into three categories.
Polyalphaolefin oils are made from carbon monoxide. No shit. Through some weird heat-and-pressure process, PAO oils fall out. These are called "true synthetics." Mobil 1 and AMSOIL are polyalphaolefin oils.
Hydrocracked oil is very highly refined mineral oil. The hydrocracking process pulls the undesirable components out of the oil. Because the oil isn't the same as regular mineral oil, they can call it synthetic even though it's really not. Castrol Syntec and Motorcraft oils are both hydrocracked. (Before they install the additive package, hydrocracked oil looks like very thick water.)
Synthetic blends...see all the way to the top.
6. Oil Change Intervals are weird. The manuals all state "normal driving" and "severe service." Severe service includes stop-and-go driving, extended idling, operation at slow speeds...yes, this is normal driving. If the manual calls for service every 5000 miles, that's all you need do. If it wants service at 3000 miles, once again that's what you do. Remember: auto warranties are a form of insurance...and did you ever see a form of insurance where the underwriter didn't try to deny every claim he possibly could?
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