What Is The Difference Between AW 46 And AW 68?

What’s really happening in your hydraulic system?

Thicker AW 68 holds up better under high heat and pressure (above 2,000 psi), keeping metal parts from touching in pumps and motors. AW 46 slips through cold systems more easily and is the usual choice for most North American tractors, skid-steer loaders, and snow plows in mild to warm weather. ISO VG 46 oils usually clock in at 41.4–50.6 cSt at 40 °C, while ISO VG 68 oils sit between 61.2–74.8 cSt. The gap is real and measurable. After startup, glance at the reservoir temperature—if it’s creeping above 160 °F (71 °C), think about switching to AW 68 if your manual says it’s okay. Never dump AW 32 into a system built for AW 68; the thin oil breaks down fast and leaks inside, sapping power and chewing up parts faster.

How to pick the right oil without spinning your wheels

1. Find the “Hydraulic Fluid Specifications” table. John Deere, CNH Industrial, and Kubota all call for AW 46 in 2024–2026 compact utility tractors used for farm and grounds work. If the manual points to “AW 68” for hot climates or constant heavy loads, go with that.
2. Match the outside temperature: AW 46 handles roughly 14 °F to 104 °F (–10 °C to 40 °C); AW 68 is meant for 32 °F to 122 °F (0 °C to 50 °C). When it dips below 0 °F, grab AW 32 instead.
3. Look at the pump type and pressure rating. Vane pumps (common in mobile gear) like AW 46. Gear and piston pumps in industrial loops above 2,500 psi run cooler and last longer on AW 68.
4. Buy branded AW 46 or AW 68 that meets DIN 51524 HLP specs. Cheap off-brand fluids often skimp on zinc dialkyldithiophosphate (ZDDP) or foam suppressors, raising the risk of cavitation and faster pump wear.

Still chasing leaks or overheating? Three fixes to try

• Flush with a proper hydraulic cleaner (Citgo Hydraulic Flush works), then refill with fresh AW 46 or AW 68 as the manual says. Mixing viscosities dilutes anti-wear additives and can slash ZDDP levels by up to 40%, speeding up pump wear. Watch the inlet vacuum; anything over 6 in Hg means the filter is choking.
• Give the oil cooler a once-over. AW 46 moves fast and thins out quicker in hot weather, sometimes pushing temps past 160 °F (71 °C) in undersized coolers. Bump up to a cooler that’s 15–20% larger if the reservoir keeps climbing.
• Test the relief valve: pop it out, wipe the poppet clean, and check the spring tension against the manual’s setting. A sticky valve can fake low-viscosity trouble. Put it back with a fresh seal kit if you spot leaks.

How to keep hydraulic headaches from ever showing up

Keep drums inside to stop water from condensing inside—free water can knock additive effectiveness down by up to 12% each month. Stick with OEM-approved AW oil; generic “hydraulic fluid” without the AW tag often leaves out the anti-wear additives pumps need. A $250 handheld viscometer gives instant numbers; STLE 2025 conference data shows tracked viscosity cuts pump failures by 29% over three years. Store spare drums sealed and upright to keep air from getting mixed in. If you're unsure about maintenance schedules, consider reading about difference between roundworms and tapeworms in dogs for insights on equipment health monitoring.