When it comes to maintaining vintage tractors or trucks, finding the right hydraulic fluid is crucial. People usually buy vintage tractors and tillage equipment 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.
Oil has also changed since the old days, and the ways manufacturers list the recommended oil today versus in the past can vary. 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 need to change the oil or hydraulic fluid in your tractor and you’re not sure which weight to buy, Blain’s Farm & Fleet is here to help with our simple SAE-to-ISO oil conversion chart.
For vintage tractors and trucks, the recommended oils are often listed using SAE weights. However, many modern hydraulic oils use ISO grades. This discrepancy can complicate maintenance without a proper conversion method.
The goal is to match the oil’s viscosity as closely as possible to what the manufacturer recommends to ensure the vehicle components are well-lubricated and functioning efficiently.
Here’s a handy chart to help you find the equivalent ISO grade for a given SAE weight:
| SAE | ISO/AW |
| 10W | 32 |
| 15W or 20W | 46 |
| 20W | 68 |
| 30W | 100 |
This oil conversion chart is approximate.
Note: ISO grades overlap with SAE weights in some cases. For instance, ISO 46 can replace both SAE 15W and 20W oils depending on the temperature.
SAE and ISO are standardized specifications that define the viscosity of oils. These standards ensure that one brand’s oil is consistent in viscosity with another’s, even if they use different labeling systems.
SAE viscosity grades are primarily used for automotive oils. They range from low-viscosity winter grades like SAE 0W and 5W to high-viscosity grades like SAE 50. The “W” indicates winter, which means the oil performs well in colder temperatures.
ISO viscosity grades, on the other hand, are mainly used for industrial lubricants. These grades are represented by numbers like ISO 32, ISO 46, and ISO 68. Higher numbers indicate higher viscosity.
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’s extremely hot, you should not use a thicker oil.
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.
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.
Understanding and converting SAE to ISO oil grades is essential for maintaining vintage tractors and trucks. By following this guide, you can ensure your vehicle receives the appropriate hydraulic fluid.
Visit our buying guide on hydraulic fluid if you still aren’t sure which one is right for your tractor.
For more guides like this one, check out our other Farm Equipment articles.
