Wood splitters use different types of hydraulic fluid depending on what the manufacturer recommends, but the truth is that most hydraulic equipment can use a variety of hydraulic fluid and still work properly. Maintaining the warranty that comes with a wood splitter does require the owner to use the recommended hydraulic fluid, however, so it is a good ideal to follow the manufacturer's recommendation until the warranty expires.
A wood splitter uses hydraulics to push the wood through the splitting device or maul. This equipment uses hydraulic fluid in order to lubricate all the pieces and keep wear on the hydraulic components to a minimum. A non-foaming hydraulic fluid is a nonflammable substance recommended by many wood splitter manufacturers such as MTD Equipment and Yard Man. This hydraulic fluid is a mixture of nature chemicals that doesn't create foam when running through the system, which in turn eliminates the creation of grit or build-up around the moving parts of the wood splitter.
Oil-based flammable hydraulic fluid is used in wood splitters to provide more power in order to split different sizes of logs or tougher kinds of wood such as hickory. Another advantage of flammable or oil-based hydraulic fluid is that it prevents corrosion of the machine's hydraulic components better. This type of hydraulic fluid is heavier, and as a result the oil-based fluid builds up in the wood splitter more often than other types of hydraulic fluid. Changing the fluid more frequently can prevent the build-up that this type of hydraulic fluid causes.
Wood splitter can also use synthetic hydraulic fluid, which is made up of a combination of man-made lubricants that are not flammable. This type of hydraulic fluid is lighter and less expensive than the others. The drawback, however, is that it corrodes the components more quickly, and causes the gaskets sealing the hydraulic fluid from leaking to wear faster. The primary benefit of synthetic hydraulic fluid is that it is not flammable. If the wood being split has a chance of causing sparks, then this is the recommended type of hydraulic fluid.