For construction machinery that has been in service for many years, overheating is a common — and often frustrating — issue. Let’s explore the problem in a practical way.

For machines that were originally well-designed and proven reliable, their hydraulic systems were fully capable of meeting normal cooling requirements when new.
(You can’t just fit a huge radiator on the system — sure, it won’t overheat, but then it may run too cold. Don’t forget, machines in cold regions even need to “wear” thick insulation in winter — like a down jacket, haha!)

In aged machines, overheating usually means that the system’s heat generation has exceeded its cooling capacity — but this is not a design flaw; it’s a sign of deterioration or malfunction. Minor “aches and fevers” are inevitable.
I personally don’t recommend randomly modifying or upgrading the cooling system — that’s usually the instinct of someone who sells radiators, haha.

1. Don’t Blame the Original Design Too Quickly

When I was young and inexperienced, I used to shout, “This is bad design!”
But with time, I learned: machine design is a result of careful engineering and repeated validation. Sure, even the best designs have flaws — if even God makes mistakes, how can humans not?
But statistically speaking, true design errors are rare. In most cases, the problem lies in operation, maintenance, or aging.

After nearly forty years in the machinery field, I no longer criticize design so easily — I’m nowhere near as capable as the engineers who designed these systems.
Don’t tell me you’re smarter than the design engineers — they’ve already considered the same problems you’ve thought of. The final design is always a balance of function, cost, materials, and overall system trade-offs, which is the chief engineer’s responsibility.

2. Why You Shouldn’t Modify the Cooling System First

Unless the original cooling system has truly failed, it’s generally not recommended to modify it.
In most cases, high hydraulic temperature comes from internal leakage, not from insufficient cooling.

If you simply force the system to cool without addressing internal leakage, you’re only treating the symptom, not the cause.
The leakage — and therefore the heat generation — will continue to worsen.

The real solution is to identify and eliminate the source of internal leakage within the hydraulic system.

3. Typical Causes of Overheating

Most overheating originates from internal leakage in the following components:

• Hydraulic pumps

• Control valves

• Actuators (cylinders and hydraulic motors)

• If only one circuit overheats, the leakage is local.

• If all circuits overheat, the leakage is likely in the main pump or main control valve.

4. A Simple Field Test Method

If you want to evaluate your machine’s performance yourself, here’s a practical way.

You’ll need a stopwatch.
(And no, don’t just use your phone — it’s too clumsy. Go buy a cheap stopwatch — about 10 RMB for a knockoff — that’s what I use, and it works fine.)

Then, find your machine’s official working cycle time data.
(Don’t be lazy — no one’s going to hand it to you for free. Technicians who won’t do their own homework don’t deserve good data — I don’t sell repairs or parts, I only talk, which makes me a gentleman — talk, not charge!)

Now, measure the actual cycle times for each hydraulic function, at least three times each, and take the average.
Compare it with the standard value:

If the actual cycle time exceeds the standard by more than 20%, it’s a sign of serious internal leakage — you’d better get a professional repair soon.

5. Recommended Circuit for Testing

Most technicians focus on the boom lifting cycle, since it’s the most direct indicator of hydraulic efficiency.

Test procedure:

1. Fully extend the boom, arm, and bucket; place them flat on the ground, just touching the surface.

2. Run the engine at full throttle.

3. Pull the control lever as fast and hard as you can while starting the stopwatch.

4. Stop timing when the boom cylinder reaches the cushioning point (you’ll hear a noticeable throttling sound).
   That’s your cycle time.

Example:

• New machine boom lift time: 3.0 seconds

• Actual measured time: 4.0 seconds
  → Efficiency = 3.0 ÷ 4.0 = 75% of original.
  The missing 25%? It turned into heat — that’s why your machine’s running a fever!

Formula:

V = L₁ / L₂
(Where V = working efficiency, L₁ = standard time, L₂ = measured time)
If V < 0.8 (80%), take it seriously.

This simple formula is enough for on-site testing.
Practice a few times — don’t tell me you can’t pull the lever and hit the stopwatch at the same time. If you can’t, go find a pro — or grow a third hand, haha!

No need to test the bucket circuit — I’m sure your bucket pins are already so worn they’ll ruin the data.

For swing tests, allow some run-up distance and mark a reference point for timing.

For travel tests, perform single-side free rotation tests — in both forward and reverse, high and low gears, at least three times each, for no fewer than three rotations per test.
(If your model has specific test procedures, follow those — don’t try to outsmart me, haha!)

6. Simple Diagnostic Observations

You can also use a few “old-school” tricks to roughly identify the cause of hydraulic overheating — believe it or not, it’s free advice anyway:

(1) If your machine overheats very quickly after a cold start, the problem is likely in the cooling control circuit — such as:

• The radiator bypass valve opening too early (like a thermostat stuck open).

• The cooling fan speed being too low (hydraulic-drive or clutch-drive issues).

(2) If it overheats after several hours of operation, the radiator is probably externally clogged — clean the fins or airflow path.
(Normally, this fault doesn’t slow down the system noticeably or trigger temperature alarms.)

(3) If some circuits slow down significantly, those circuits have serious internal leakage.

(4) If all circuits slow down, the hydraulic system is severely worn — time to rebuild the pump, valve, motor, and cylinders.

(5) Sometimes, aging electrical control causes slow operation — e.g., worn proportional solenoids or pump control valves.
You can test this by switching to a backup control mode or manual override.

(6) (New addition!)
Here’s a simple but highly reliable qualitative test:

• If, when oil temperature rises (but before the warning limit), operation speed remains stable, the problem is likely in the cooling system or its control circuit — check there first.

• If, as temperature rises, all motions noticeably slow down, it’s hydraulic component wear — and only repair or replacement can fix it.
  Don’t hope to “adjust” your way out of wear — if adjustments could restore worn components to new condition, parts dealers and OEMs would all go out of business!