Vintage tractors and tillage equipment are usually bought at auctions, so collectors don’t always have access to their owner’s manuals. Owner’s manuals are important because they include the tractor’s specifications, replacement parts, and which oil it requires. Also, oil has changed since the old days, and the way manufacturers list the recommended oil is sometimes different from the way oils are labeled now. Often, the hydraulic oil for an older tractor is listed using an SAE oil weight. This would not be a problem if hydraulic oils weren’t labeled using the ISO system now, but they are. If you bought a tractor and need to change the oil or hydraulic fluid, and you’re not sure which weight to buy, here is a helpful oil conversion chart that may make things easier.
Oil Conversion Chart
15W or 20W 46
This oil conversion chart is approximate.
Oil in extreme temperatures
Depending on the temperature you run your engine in, you may want to use a slightly thicker or thinner oil. In very cold weather, you may want to use a thinner hydraulic oil, because the cold thickens your oil. However, even if it is extremely hot, you should not use a thicker oil.
It’s important to get the right hydraulic oil for your tractor or truck to make sure that the hydraulics work well and last for a long time. Only use this chart to find an oil equivalent to the manufacturer’s recommended oil for your tractor or truck. You may notice that ISO 46 can replace both 15W and 20W SAE oils. This is because the ISO specifications are broad, and they overlap with SAE weights in some cases. If your tractor or truck calls for 20W hydraulic oil, it may be best to use the thicker ISO 68 in hot temperatures and thinner ISO 46 in cold weather.