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Truck Topics

The Tool Box - Oil

By Bob Caffee
Posted Mar 29th 2011 5:37AM
Oil - Which one is best?

Oil is one of those things most people don't think about too much. A recent post got me to thinking about oil and oil additives. Is the oil you are using the right one? The oil companies that refine oil must meet or exceed the API (American Petroleum Institute) standards. Now does this mean all oil is the same? Absolutely not, however, every oil that is manufactured that meets the same spec must be compatible with each other. Does this mean you should mix different brands? Not if you have a choice. Could you? Yes, in an emergency.

Let's say you use Shell Rotella, you check your oil level and find its low enough to need topped up. You find the service station your oil is sold out but they have Chevron Dello. is it ok to run a gallon low? I don't like to and I wouldn't recommend doing so. Can you add the Dello to get you by? Yes, will it hurt anything? Most likely not, each manufacturer has chemists that all they do all day long is mix different additives together to get the right mix of chemicals and petroleum for the best performance and least cost  that will meet spec. Each oil has different amounts of different additives to get the same job done. Mixing different brands may cause an imbalance in this chemical cocktail, turning a once good mix into something very different, and possibly very bad, for your engine. This is why it is recommended you know what oil brand and weight that is in your truck, and not mix. Using the same brand and different weights is better than mixing brands, as long as they are the same spec.

Let's talk about the API spec. This is required to be on every package of oil sold in order to identify what the oil is to be used for. The API service symbol looks like a donut and it tells you if the oil is right for you, if you know how to read it and know what you need.

We will start with the top half of the "donut" this is where you will see something like "API service CJ-4/ SL". The "C" means it can be used in a Commercial engine. Years ago I was taught it meant compression ignition, which is how a diesel fires. "J-4" is the service category. The "S" is for Service (I was taught for spark ignition of gasoline engines) which means this oil can be used in a gasoline engine also, and the L is the service category. I was taught you cannot use a "diesel" oil in a gas engine, as we can see this is not true as long as the oil has the service standard on the container certifying as much. Years ago this may have been true but not anymore.

The bottom half of the "donut" is where anything special is posted such as Energy Conserving or CJ-4 Plus, the Plus being extra protection against soot buildup. The "donut" hole is where you will find the SAE (Society of Automotive Engineers) viscosity grade, something like 15W/40. The viscosity grades are determined by using a viscometer using the testing standards set by the SAE. To explain, the 15W (W is for winter) is the performance of the oil, after being cooled, of a 15 weight oil, and the 40 is the viscosity of the oil at 210 degrees F. I've heard people say they wouldn't use a 15W/40 oil because it's to thin when in fact it's only thin when it needs to be, when it's cold. A 15W/40 oil has the same viscosity as a straight 40 weight at 210 degrees F, engine operating temperature.

So now we know how to read an API symbol. Let's talk about synthetic oils. These oils must also meet the minimum standards for performance like every other oil to receive the API rating. Most Synthetic oils are not exactly what they say they are, or should I say they are not 100% synthetic. There are only two brands that I found that are 100%: Royal Purple and Amsoil. There may be others but I didn't find them. 100% synthetic is an oil that contains no paraffin bases (crude oil bases). They may have some iso-paraffinic dilutents but no petroleum bases. The other synthetic oils are actually a blend of synthetic and petroleum bases, using mostly synthetic additives for the best performance. These oils are usually three or more times the price of standard motor oils.

So you ask, why would I use synthetic when standard oil will do just fine? I will answer to the best of my knowledge. Using synthetic oil will give you superior protection against wear. By nature, it is thinner so it is easier to pump through the engine. It typically keeps the engine cleaner due to the additives. They typically keep contaminates in suspension better so the filters can do a better job of cleaning the oil. According to all the studies I have seen they will improve fuel mileage noticeably.

With that said, I would not recommend using synthetic oils unless a by-pass filtration system is used to extend drain intervals. I do not believe it would be cost effective to drain synthetics at the normal intervals of 15,000 to 25,000 miles of standard oils. There are "synthetic blends" that are less expensive and give some of the benefits that a "full synthetic" will give; these are cost effective to use without the by-pass filtration system.

As I said earlier mixing oil may not be such a good thing, so here is a quote from Royal Purples web site. "Engine oils are formulated with a fine balance of additives (antifoam, corrosion inhibitors, anti-wear, detergent/dispersants, oxidation inhibitors) and more isn't necessarily better. The use of an oil additive could upset the balance resulting in reduced performance." To me an additive is a bad thing. An oil distributor I used to work with told me once," if you feel you need to add something to your oil to make it better, you are using the wrong oil". I recommend using a good synthetic oil with a by-pass filtration system, do regular oil analysis, and not change your oil unless the lab tells you, you need to. For those who are "green" this will help in saving the environment by fewer oil drains.


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