Introduction
Proper hydraulic oil maintenance is critical to the longevity and reliability of the Caterpillar AP655F asphalt paver. Regular fluid changes prevent contamination from degrading pump performance, valve operation, and screed control, which directly affects mat quality. This article provides a comprehensive step-by-step guide to changing the hydraulic oil on the AP655F, including safety precautions, fluid specifications, and cost considerations in British Pounds (GBP).
Why Is Regular Hydraulic Oil Change Important for the AP655F?
The hydraulic system on the Caterpillar AP655F powers essential functions including the screed extenders, augers, conveyor drives, and steering. Over time, hydraulic oil degrades from thermal stress, moisture ingress, and particulate contamination. If left unchanged, degraded oil can cause erratic screed behaviour, reduced conveyor torque, and premature pump wear. Following the manufacturer’s recommended interval—typically every 2,000 operating hours or annually—ensures consistent paver performance and protects your investment. For additional insights on maintaining screed components, refer to our guide on Caterpillar AP655F Screed Plate Wear Indicators: A Practical Guide.
What Tools and Materials Are Needed for the Hydraulic Oil Change?
Before beginning the procedure, gather the following items. Using the correct specification oil and clean tools prevents contamination. All prices quoted are in GBP and reflect typical UK market costs as of early 2025.
| Item | Specification/Type | Approximate Cost (GBP) |
|---|---|---|
| Hydraulic oil | CAT HYDO (SAE 10W) or equivalent ISO VG 32 | £85–£120 per 20-litre pail |
| Drain pan (minimum 40 litres) | Heavy-duty steel or plastic | £30–£50 |
| Wrenches | Metric combination set (10–24 mm) | £25–£50 (set) |
| Torque wrench | 10–150 Nm range | £60–£120 |
| Filter wrench | For OEM hydraulic filter | £15–£25 |
| New hydraulic filter | CAT 1R-1807 or equivalent | £35–£55 |
| Clean rags and absorbent pads | Lint-free, oil-absorbent | £10–£20 |
| Safety gloves and goggles | Chemical-resistant | £10–£18 |
| Transfer pump (optional) | Hand-operated or electric | £20–£70 |
Note: Total investment for a single oil change is roughly £160–£250, depending on oil quantity and filter costs. The AP655F hydraulic system holds approximately 110 litres of oil.
What Is the Step-by-Step Procedure for Draining the Hydraulic Oil?
Follow these steps carefully to ensure a clean and safe drain. Always refer to the machine’s service manual for your specific serial number prefix.
1. Prepare the Paver
Park the AP655F on a level surface. Engage the parking brake and lower the screed to the ground. Allow the hydraulic system to cool to 50°C or below to avoid burns. The oil should be warm enough to flow freely but not hot.
2. Locate and Remove the Drain Plug
Position the drain pan under the hydraulic tank drain plug, typically located at the bottom of the tank on the right-hand side near the engine. Use a 19 mm wrench to slowly loosen the plug. Allow the oil to drain completely. Inspect the plug’s O-ring for damage and replace if necessary.
3. Remove and Replace the Hydraulic Filter
Using a filter wrench, unscrew the hydraulic filter canister. Allow residual oil to drain into the pan. Clean the filter mounting surface. Lightly coat the new filter’s gasket with fresh hydraulic oil. Hand-tighten the filter until the gasket contacts the sealing surface, then turn an additional three-quarters of a turn.
4. Inspect Drain Plug Contamination
Check the drained oil for metallic particles or sludge. If significant debris is present, consider flushing the system—this may indicate internal wear. For more detail on diagnosing unusual noises that often accompany wear, read the Caterpillar AP655F Screed System Noise Diagnosis Guide.
How to Properly Refill and Prime the Hydraulic System?
Once the old oil is drained and the filter replaced, refilling must be done systematically to avoid air locks.
1. Add Fresh Oil
Remove the hydraulic tank filler cap. Pour fresh oil slowly using a funnel or transfer pump. For the AP655F, approximately 110 litres of CAT HYDO (or equivalent ISO VG 32) are required. Add oil in stages and check the tank sight glass. The level should be at the “COLD FULL” mark initially.
2. Prime the System
Start the engine and let it idle at low RPM. Operate the screed extenders, augers, and conveyors one at a time to purge air. Cycle each function three to five times. Air in the system causes jerky movement and can damage pumps. Perform this procedure slowly.
3. Recheck Oil Level and Torque Drain Plug
After priming, turn off the engine and wait two minutes. Recheck the sight glass and top up to the “HOT FULL” mark if needed. Torque the drain plug to 35 Nm. For more on the conveyor system that relies on these hydraulics, see Caterpillar AP655F Conveyor Belt Maintenance: Essential Tips for Longevity.
What Are the Key Safety Precautions During the Oil Change?
Hydraulic oil at high temperature can cause severe burns. The oil itself may be under residual pressure even when the engine is off. Always loosen the filler cap slowly to release pressure. Wear chemical-resistant gloves and safety goggles. Clean up spills immediately with absorbent pads to prevent slip hazards. Dispose of used oil and filters at a licensed waste facility. For further operator safety considerations, the Caterpillar AP655F Operator Comfort: A Detailed Review discusses ergonomic features that reduce fatigue during maintenance tasks.
What Do Owners Say About the AP655F Hydraulic System Maintenance?
Experienced operators and fleet managers generally praise the AP655F’s hydraulic system reliability, provided that oil changes are performed on schedule. Common feedback includes:
- Ease of access: The drain plug and filter are reasonably accessible, though the filter can be tight on early-model machines. Owners recommend using a strap wrench for better grip.
- Oil consumption: The 110-litre capacity is manageable, but operators note that using the correct viscosity (ISO VG 32) is critical. Some aftermarket oils cause pump cavitation in cold weather.
- Filter changes: Many owners change the hydraulic filter every other oil change to reduce costs, but Caterpillar recommends replacing it with every service.
- Contamination awareness: Operators who work in dusty environments report needing more frequent changes—sometimes every 1,500 hours. For conveyor-related issues tied to hydraulics, see the Caterpillar AP655F Conveyor Belt Tension Adjustment Guide.
Frequently Asked Questions About the Caterpillar AP655F Hydraulic Oil Change
1. How many litres of hydraulic oil does the AP655F require?
The system capacity is approximately 110 litres. Always verify using the sight glass after priming.
2. Can I use a different hydraulic oil brand than Caterpillar HYDO?
Yes, but ensure it meets ISO VG 32 grade and Caterpillar’s TO-4 specification. Substandard oil degrades pump life.
3. How often should I change the hydraulic filter on the AP655F?
Caterpillar recommends replacing the filter at every oil change. Using a dual-filter kit is optional but extends service intervals.
4. Why does my AP655F hydraulic system make noise after an oil change?
Air trapped in the system causes cavitation. Cycle all hydraulic functions at low idle until the noise stops. To diagnose persistent noise, consult the Caterpillar AP655F Screed System Noise Diagnosis Guide.
5. What happens if I overfill the hydraulic tank?
Overfilling causes foaming, overheating, and potential seal damage. Always fill to the correct mark on the sight glass.
6. Can I flush the system with a cleaning solvent?
No. Use only the specified hydraulic oil for flushing. Solvents leave residues that damage seals and valves. If contamination is severe, contact your Caterpillar dealer.
For any issues related to the transmission system that may interact with hydraulics, refer to the Caterpillar AP655F Transmission System Troubleshooting Guide.