For older construction machinery, overheating of hydraulic systems is a common issue and a frequent headache. Let’s discuss some causes and simple inspection methods.

For mature and well-established machines, the original design already fully meets the cooling requirements of the hydraulic system. You can’t just add a huge cooling system—sure, it won’t overheat, but then the system could become too cold. Haven’t you seen machines in cold regions wear thick insulation blankets in winter? (Not a down jacket, but insulation blankets, haha.)

For older machines, as efficiency declines, the heat generated can exceed the machine’s original cooling capacity. This isn’t a design flaw—it’s a fault in the machine itself, usually minor but inevitable. I don’t recommend modifying the cooling system on a whim—probably something a radiator salesperson would suggest, haha.

When I was younger and less experienced, I used to complain: “The machine design is unreasonable!” In fact, every machine design goes through meticulous planning and repeated validation. Mistakes can happen, even from the best designers—but the probability is very low. Most problems stem from usage and maintenance. I’ve worked in machinery for nearly forty years, so I don’t make such claims anymore—I’m far less skilled than the designers. Whatever issues you think of, designers have likely already considered, but compromises are made due to cost, materials, or overall balance—these are decisions of the chief designer.

In practice, unless the original cooling system fails, I generally don’t recommend modifying it. When a hydraulic system overheats, the main cause is usually internal leakage due to efficiency loss—not the cooling system itself. Forcing cooling without addressing the root cause will worsen the leakage, and temperatures will continue to rise. The real solution is to identify and fix the source of internal leakage.

Most causes of overheating are internal leakage in the hydraulic pump, valve blocks, and actuators (cylinders and motors).

• If only a single circuit overheats, it’s local leakage.

• If all circuits overheat, it’s likely the hydraulic pump or main control valve.

If you can perform basic performance testing on the overheated machine, it becomes clear. This requires a stopwatch—don’t tell me your phone works fine; it’s not flexible enough. Buy a simple stopwatch—about 10 RMB on the market; I use one and it works perfectly.

Also, you need to find the machine’s specific performance parameters yourself (don’t be lazy expecting ready-made answers—no good colleague will give you free info, and I won’t either). Measure each working circuit’s cycle time carefully, preferably three times, and average the results. Compare this to standard values. If the measured cycle time is 20% longer than the standard, internal leakage is serious, and professional service may be needed—don’t expect me to fix it; I only offer advice, haha.

A practical focus is the boom lifting time, as it’s the most intuitive and efficiency-critical measurement.

Testing Method:

• Extend the boom, stick, and bucket fully and place on the ground, just in contact.

• Full throttle, pull the control lever as fast as you can while pressing the stopwatch start button. Stop timing when the boom cylinder begins to enter the cushion stage (you’ll hear a distinct throttling sound). This gives the cycle time for that circuit.

Example:
For a certain model, the boom lifting cycle time on a new machine is 3 s. If measured at 4 s on your machine, its efficiency is only 75%, and the remaining hydraulic energy turns into heat, causing overheating.

Formula:

$$\text{Efficiency}V=\frac{L_1}{L_2}$$

where $L_1$ = standard cycle time, $L_2$ = measured cycle time. If efficiency < 80%, pay attention.

Practice this several times to coordinate stopwatch and lever control—otherwise, seek a professional. For older machines, you can skip bucket cycle tests—the pins are likely worn and results unreliable.

• Swing Test: Allow a run-up distance, start moving, and measure according to the machine manual or ruler.

• Travel Test: Use single-side free rotation, testing high/low gears and forward/reverse three times each, leaving a run-up distance.

Ignore advice that only tells you to send the machine for repair without diagnosis—be cautious of profit-driven motives. I have no such conflict of interest, so you can trust this advice.

Simple Detection Methods for Hydraulic Overheating:

1. High temperature right after cold start: Likely a cooling system control element failure, e.g., bypass valve opens too early (similar to an engine thermostat), or fan speed too low (hydraulic or clutch-driven).

2. Overheating after several hours of operation: Likely clogged radiator fins—cleaning is generally effective. Note: in this case, cycle speed usually doesn’t drop significantly.

3. Cycle speed reduction in specific circuits: Indicates severe internal leakage in those circuits.

4. All circuits slow after overheating: Indicates severe hydraulic wear—pump, valves, motors, and cylinders require repair.

5. Aging of certain electro-hydraulic controls: e.g., proportional solenoids—can be diagnosed using a backup switch.