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APRIL 09, 2025

Maxon GPT Liftgate Maintenance: Essential Hydraulic Fluid Tips

Your Maxon GPT is a workhorse—but like any hydraulic system, it depends on clean, properly maintained fluid to function at full capacity. Over time, hydraulic fluid can break down, become contaminated, or leak, causing slower lift speeds, unresponsive controls, and even total lift failure.

Ignoring hydraulic maintenance is one of the fastest ways to shorten the lifespan of your liftgate. But the good news? Checking and changing hydraulic fluid is simple when you know what to look for.

This guide will walk you through:

• How to check hydraulic fluid levels in a Maxon GPT liftgate
• When and how to change hydraulic fluid
• The best hydraulic fluid for Maxon liftgates
• Common signs of hydraulic system problems
• How to bleed air from the hydraulic system after a fluid change
• Common mistakes to avoid when changing hydraulic fluid
• What to do if your hydraulic fluid is leaking

Let’s dive into everything you need to know to keep your lift gate running smoothly!


Disclaimer:

The information provided in this article is based on content from official Maxon manuals, specifically:

- M-08-35B-EO13337 (2010)
- M-08-04A-EO13308
- M-08-03A-EO13308

While these guidelines are derived from these manuals, it’s important to remember that each liftgate model may have unique specifications and maintenance requirements. For the most accurate and personalized guidance, always refer to your specific Maxon liftgate manual and contact Maxon customer support directly.

LiftGateMe is dedicated to providing helpful and accurate information, but it’s essential to follow the manufacturer’s recommendations to ensure safety and optimal performance.

1. How to Check Hydraulic Fluid Levels in a Maxon GPT Liftgate

Hydraulic fluid is the lifeblood of your Maxon liftgate. If levels get too low, the liftgate may struggle to raise or lower properly. If the fluid is dirty or contaminated, it can clog the system, leading to slow operation or component failure.

Step-by-Step: Checking Hydraulic Fluid Levels

• 1️⃣ Park the truck on level ground and turn off the engine.
• - This ensures an accurate reading and prevents accidental movement​.
• 2️⃣ Locate the hydraulic reservoir.
• - The reservoir is inside the pump box, usually mounted on the right hand side of the gate frame.
• 3️⃣ Remove the fill cap and inspect the fluid level.
• - The fluid should be between the minimum and maximum marks on the sight gauge shown on the fluid reservoir​.
• 4️⃣ Check the fluid color.
• - Clean fluid should be light amber or clear, as most Maxon fluids typically have this appearance. However, aftermarket fluids can vary significantly—they may be orange, blue, red, purple, or almost any other color.
• - Signs of contamination include fluid that appears milky, grainy, gritty, or has bubbles on top accompanied by an off-color compared to the rest of the fluid. If you notice any of these signs, it’s time to replace the fluid.
• 5️⃣ Top off fluid if necessary.
• - Use only Maxon-recommended hydraulic oil (more on this below) and never mix different types of fluid​.

🚨 Warning: Never operate the liftgate with low or contaminated hydraulic fluid—this can cause severe damage to the pump, cylinders, and hoses​.

2. When to Change Hydraulic Fluid in a Maxon GPT Liftgate

Just like engine oil, hydraulic fluid degrades over time. Dirty or old fluid can lead to overheating, sluggish liftgate performance, and even component failure.

How Often Should You Change Hydraulic Fluid?

• 🔧 Every 12 months or sooner if contamination is detected​.
• 🔧 Immediately after hydraulic system repairs (such as replacing hoses or cylinders)​.
• 🔧 If fluid appears dark, sludgy, or milky (signs of water contamination)​.

🚨 Neglecting regular fluid changes can lead to premature pump and cylinder failure, resulting in costly liftgate cylinder repair or other avoidable maintenance expenses for your gate.

3. How to Change Hydraulic Fluid in a Maxon GPT Liftgate

Step-by-Step: Changing Hydraulic Fluid

• 1️⃣ Lower the liftgate to the ground.
• - This relieves pressure in the system and ensures a complete fluid drain​.
• 2️⃣ Turn off the truck engine and disconnect power.
• - Prevents accidental activation of the lift gate switch​.
• 3️⃣ Drain the old hydraulic fluid.
• - Remove the drain plug from the reservoir and let the fluid fully empty into a waste container​.
• 4️⃣ Inspect the reservoir for debris or sludge buildup.
• - If dirty, clean the reservoir with a lint-free cloth before refilling​.
• 5️⃣ Replace the hydraulic filter (if applicable).
• - A clogged filter can reduce liftgate performance—always install a new one when changing fluid​.
• 6️⃣ Refill with Maxon-approved hydraulic oil.
• - Do not overfill—fill only to the recommended level on the sight gauge​.
• 7️⃣ Reconnect power and cycle the liftgate several times.
• - This removes air bubbles from the system and ensures proper hydraulic flow​.

4. What Hydraulic Fluid Should You Use?

Using the right hydraulic fluid is just as important as changing it on time. Incorrect fluid can cause excessive wear, leaks, and system malfunctions.

Recommended Hydraulic Fluid for Maxon GPT Series

✅ Use ISO 15 or ISO 32 or hydraulic oil 
✅ Do NOT mix different brands or types—this can cause foaming and overheating​.
✅ In colder climates, use a low-viscosity hydraulic fluid for better cold-weather performance​.

We have a complete hydraulic liftgate fluid guide just for you.

🚨 Using the wrong fluid can void your warranty and lead to costly damage​. As always, refer to the manual which came with your specific liftgate or contact our team or manufacturing for further verification.

Maxon's GPT Maintenance Manual from edition M-08-35, Rev B in Aug 2010 lists these two sources for the preferred hydraulic oil.

Note: Ensure you use the correct grade of hydraulic fluid for your location and lift gate.

• +50 to +120 Degrees F - Grade ISO 32 
• Below +70 Degrees F - Grade ISO 15 or MIL-H-5606

ISO 32 Hydraulic Oil Table

ISO 15 or MIL-H-5606 Hydraulic Oil Table

5. Common Signs of Hydraulic System Problems

Even with regular liftgate maintenance issues can still arise. If you notice any of these warning signs, it’s time to inspect your hydraulic system to avoid costly liftgate repair:

• ⚠ Liftgate raises slowly or struggles with loads → Fluid level may be low​.
• ⚠ Liftgate doesn’t lower properly → Hydraulic fluid may be contaminated​.
• ⚠ Noisy pump or whining sound → Air in the system or dirty fluid​.
• ⚠ Fluid leaking from hoses or fittings → Possible loose connections or worn-out seals​.

6. How to Bleed Air from the Hydraulic System After a Fluid Change

Think of monthly maintenance as your preventative deep dive—it’s a more thorough check-up that ensures core liftgate components remain in top working condition.

Step-by-Step: Removing Air from the Hydraulic System

• 1️⃣ Lower the liftgate completely to release system pressure​.
• 2️⃣ Refill the hydraulic reservoir to the correct level after the fluid change​.
• 3️⃣ Cycle the liftgate up and down at least 5 times without a load to push air out​.
• 4️⃣ Check the fluid level again and top off if necessary​.
• 5️⃣ Listen for unusual noises—whining or bubbles in the fluid indicate air is still present​.

🚨 Warning: Never overfill the reservoir—overfilling can cause foaming and reduce liftgate efficiency​.

7. Common Mistakes to Avoid When Changing Hydraulic Fluid

We hear and see a lot of seasoned operators make avoidable mistakes when servicing their Maxon tuck-under lift gate. Because of that, here are some common errors and how to prevent them:

By avoiding these mistakes, your liftgate will perform better, last longer, and stay problem-free.

8. What to Do If Your Hydraulic Fluid is Leaking

Hydraulic leaks aren’t just messy—they can cause serious performance issues and lead to liftgate failure. If you notice a fluid leak, follow these steps to diagnose and fix it.

Troubleshooting a Hydraulic Leak

• Identify the leak source:
• Check hose fittings, cylinder seals, and pump connections for fluid buildup​.
• Tighten loose fittings:
• Most leaks occur at connection points—use a wrench to tighten them without over-tightening​.
• Inspect hydraulic hoses for cracks or wear:
• If a hose is damaged or brittle, replace it immediately to prevent a system-wide failure​.
• If the pump is leaking fluid:
• A worn pump seal may need replacement—verify it’s the pump seal and contact LiftGateMe, to see if a replacement seal may be available.

Never operate a liftgate with an active hydraulic leak—this can lead to catastrophic pump or cylinder failure​.

For further assistance, we have a guide for Maxon liftgate troubleshooting, specifically your GPT.

Conclusion

Your Maxon lift gate is only as reliable as the hydraulic system powering it. By regularly checking fluid levels, changing old or contaminated hydraulic fluid, and using the right oil, you ensure smooth, safe, and efficient operation—day in and day out.

So, what’s your next move?

Take five minutes today to check your hydraulic fluid—is it at the proper level? Is it clear, or does it look dirty? A quick check now can save you from a costly breakdown later.

Have questions? Contact our team today!