Two very common types of hyd oil are R&O oil and AW oil. R&O hyd oil has additives to prevent Rust & Oxidation, hence the name. AW oil has the same additives as R&O oil, but has Anti Wear additives as well and doesn't cost that much more. Then there is the ISO grade of 22, 32, 46, and 64, which reflect the viscosity of the oil. In most area of N America, and AW32 or AW46 will work just fine. Overheating and thinning of the oil is usually not an issue on Bobcats as they use an oil cooler. Not sure what oil Wal Mart has, but NAPA and other Auto Parts have AW hyd oil. I would choose a good oil though. I've used Super S brand AW oil, and when you empty the bucket, you can see residue at the bottom of the bucket. I've used higher quality oils (Shell, Conoco, Chevron) and the bucket is clean at the bottom. I think Valvoline produces oil for NAPA, good brand as well.
