There are few things people debate about more when it comes to car maintenance than oil. How do you know which oil to use in your vehicle, and should you consider switching to synthetic?
Donuts, Numbers and Standards
The engine in your car was designed to use oil with a specific viscosity that meets a set of industry standards. To make finding the right oil easier, all oils that are tested using American Petroleum Institute (API) methods have a “donut” on the back of the bottle that lists everything you need to know to pick the right oil.
The top of the donut lists the service category of the oil. For most gasoline engines, finding the right formula is easy since all API “S” categories are backward compatible. If you buy an oil that meets the latest “SN” standard, it will work in anything from the latest model to a pre-war classic. Some foreign-designed engines use ILSAC’s GF standards. This will be listed separately on the label, but if you see “Energy Conserving” on the bottom of the donut and it’s an SN category oil, it also meets the latest GF-5 standard. Like the API standard, the GF categories are backwards compatible.
With diesel engines, it’s a little more complicated. FA-4 is formulated specifically for new diesel engines. If your owner’s manual specifies this service category, it’s the only one you should use. CK-4 is the latest standard for oils used in most other diesel engines, replacing CJ-4. If your owner’s manual specifies anything other than FA-4, it is always safe to use this oil. A few companies have issued service bulletins stating that FA-4 is OK in their older engines, but when in doubt, stick to CK-4.
The oil weight is in the center. This is measured using a standardized flow test. The “W” stands for “Winter.” The number before it is the viscosity at 32ºF, and the number after it is the viscosity at 212ºF. Check your owner’s manual for the manufacturer’s recommended viscosity.
What Makes an Oil Synthetic?
Crude oil is made up of hydrocarbon chains in a wide range of sizes. Through distillation, these chains are sorted to make different products. Motor oil uses hydrocarbon chains that have between 18-34 carbon atoms.
This base oil includes every type of molecule in this size range, but some molecules vaporize in extreme heat, leading to oil burning and sludge, while others thicken at low temperatures, causing problems in extreme winter weather. Synthetic formulas are made exclusively with filtered and manufactured molecules that don’t have these drawbacks.
What about synthetic blend oils? There’s no standard for this labeling, so it could be mostly synthetic or have just a drop of synthetic in every 50-gallon barrel.
Can Switching to Synthetic Oil Cause Problems?
No. There should be no difference in how a new engine breaks in when using either conventional, synthetic or synthetic blend oil, and it won’t leak out of worn seals on high mileage engines any more than conventional oil.
Can I Change My Oil Less Often if I Switch to Synthetic?
No. While the oil itself may not break down as fast as conventional oil, it still needs to pick up dirt and other contaminants from the engine and deposit them in the oil filter. By the time you’re due for an oil change, the oil and filter are saturated with dirt, and using them for extended periods of time will increase engine wear.
When Should I Use Synthetic?
Synthetic base oil is needed to make a low viscosity oil. If your car needs 0W20 or 0W30 oil, it must use synthetic.
The stability of synthetic helps it flow at extremely low temperatures. However, it rarely gets cold enough here to see any major benefit. If you plan on going somewhere with temperatures well below zero, it’s a good idea to make the switch.
Thanks to its heat resistance, synthetic oil is less prone to forming sludge and burning off. Switching to a synthetic can reduce oil consumption in high mileage engines.
When You Have an Accident, You Need Merton Auto Body
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