That Overheating Light on Your 705A-4
From the outside, it looks like a simple fix—clean the radiator, check the coolant, maybe replace a sensor. The reality is that on Komatsu graders, especially the 705A-4 model, overheating often has nothing to do with what you can see from the service bay.
People assume the job site is the problem. Dust, debris, maybe a plugged core. What they don't see is the chain reaction that starts three feet away from the radiator, inside a component most operators rarely think about: the final drive motor.
What Most People Miss
It's tempting to think overheating is a cooling system problem. But the "check the radiator first" advice ignores how the entire drivetrain contributes to thermal load. When I took over equipment purchasing in 2022, our grader was overheating on a three-hour shift. The dealer said radiator. Our mechanic said water pump. We spent about $1,200 on parts and labor for that round of guesses.
It wasn't until we pulled the undercarriage inspection report that I saw the pattern. The temperature spike always correlated with load, not ambient temp. And the load wasn't from the blade—it was from the final drive fighting resistance it wasn't designed for.
The Real Culprit: Final Drive Load
Here's what I mean. The Komatsu grader 705A-4 has a hydraulic system that feeds the final drives. When the drivetrain binds—say, from worn undercarriage parts or misaligned track tension—the hydraulic system compensates by increasing pressure. That extra pressure creates heat. And that heat dumps back into the cooling system.
So you clean the radiator. You replace the thermostat. The temp drops a degree or two. But the root problem? The final drive motors are working at 110% because the undercarriage is dragging. The grader doesn't need better cooling. It needs the drivetrain friction reduced.
The Cost of Ignoring This
The third time our 705A-4 overheated, I finally created a diagnostic checklist that doesn't even look at the radiator until we've ruled out drivetrain drag. Should have done that after the first time. Let me rephrase that: the first two repairs cost about $800 each, and neither solved the problem. The third fix—replacing worn final drive motor seals and adjusting track tension—cost $2,400. But it worked.
The initial approach cost us about $800 × 2 = $1,600 in wasted repairs, plus the production downtime. The correct fix cost more upfront but eliminated the recurring problem. Net savings: about $2,000 over three seasons. But the real cost was the frustration—no one wants to explain to operations why the same machine is in the shop again.
Why This Matters for Your Budget
Total cost of ownership includes more than the base product price. It includes the time your mechanic spends on wrong guesses, the downtime of a machine that should be working, and the potential for cascading damage when a problem isn't solved correctly.
When you look at a komatsu grader for sale, or you're pricing a 290 komatsu excavator specs sheet, the initial number is just the entry point. The real question is: how much does each hour of operation actually cost? And that number changes dramatically when you have a chronic issue like this.
The Fix That Worked for Us
Honestly, the solution was less about parts and more about process. We:
- Started logging hydraulic fluid temperature separately from coolant temp. A 20-degree difference between them usually means drivetrain drag, not cooling failure.
- Checked final drive motor case drain flow during the overheating symptom. High flow = internal leakage = heat generation.
- Made undercarriage alignment the first checkpoint on any overheating complaint. Adjusting track tension alone fixed the problem two out of three times last year.
We still use our online parts suppliers for the actual components—Komatsu genuine parts for the final drive motors, OEM-grade undercarriage wear parts. But the diagnostic shift was free. It just required admitting that the radiator wasn't the problem.
When You Should Still Check the Radiator
I'm not saying cooling systems never fail. If the machine runs hot at idle, with no load, the radiator is probably plugged. If the temperature spikes only under load, start looking at what's creating that load. It's usually not the blade work.
This is where the boundary of my expertise matters. I know purchasing, vendor evaluation, and the financial consequences of wrong diagnostics. I'm not a mechanic. But I've learned that when a problem has been "fixed" twice and isn't resolved, the problem isn't what everyone assumed it was.
For Komatsu graders, especially the 705A-4, the cooling system isn't the star of this show. The final drives are. Check them first. Save yourself the $800 of guesswork.
