A 2019-model wheel loader experienced intermittent hydraulic pressure loss during bucket lift operations. The machine had 8,500 hours on the clock and was operating in a construction site with mixed soil conditions.
The loader operator reported that the bucket would lift slowly, then suddenly lose pressure and drop. The issue was intermittent-sometimes it happened, sometimes it didn't. It was worse when the machine was hot and the hydraulic oil was at operating temperature.
?? Warning Signs to Watch For
Intermittent pressure loss during heavy operations
Slower-than-normal lift speed
Loss of pressure when the machine is hot
Hydraulic oil temperature running higher than normal
We started with a visual inspection. Nothing obvious-no leaks, no damaged hoses, no cracked fittings. The hydraulic oil looked clean and at the correct level.
Next, we checked the hydraulic pressure with a gauge. Here's what we found:
System pressure: 2,800 PSI (normal is 3,000–3,200 PSI)
Return line pressure: 1,200 PSI (normal is 800–1,000 PSI)
Oil temperature: 185°F (normal is 150–170°F)
Higher-than-normal oil temperature indicated a restriction somewhere in the system. And the lower system pressure confirmed it.
"When you see higher oil temperature and lower system pressure, think restriction first. That's usually where the problem is."
We traced the restriction to the main relief valve. The valve was partially stuck open, allowing oil to bypass the system and return to the tank before it could build up pressure.
How did it get stuck? The valve seat was worn. Over time, the high-pressure hydraulic oil had eroded the valve seat, creating a tiny gap. When the valve tried to close, it couldn't seat properly, so oil leaked past.
This is a common issue in loaders that operate in dirty conditions. Dust and debris can get into the hydraulic system and damage precision components like valves.
We replaced the main relief valve with a new one from the manufacturer. We also replaced the valve seat to ensure a proper seal.
After the replacement, we tested the system again:
System pressure: 3,150 PSI - within normal range
Return line pressure: 950 PSI - within normal range
Oil temperature: 165°F - within normal range
The loader was back to full capacity. No more pressure loss, no more slow lifts.
To prevent this issue from happening again, we recommend:
Change the hydraulic oil every 2,000 hours-more often if the machine operates in dirty conditions.
Install an oil filter with a finer micron rating.
Inspect the relief valve during every major service.
Keep the hydraulic system clean-no working around the machine with open oil containers.
Intermittent hydraulic issues are often symptoms of a larger problem. Don't just chase the symptom-trace the root cause. Higher oil temperature and lower system pressure almost always point to a restriction. Find it, fix it, and prevent it from coming back.
