You head to the construction site or field in the morning. For the first two hours, the excavator or tractor is eager to work, and the cylinder movements are lightning fast. However, the higher the sun in the sky, the more sluggish the equipment becomes. The machine loses power, the pump starts whining ominously, and a distinct smell of overheated oil emanates from around the tank. Sound familiar?
The phenomenon of "weakening after warming up" is one of the most common problems reported by operators. Ignoring it is a direct path to pump seizure and a major overhaul of the system. BRhydraulic experts have examined cooling systems. Learn where the murderous heat comes from, what high temperatures do to the inside of the machine, and why an oil cooler is your best friend.
1. Where does the boiling water in the system come from?
A hydraulic system is, in simple terms, a system for converting mechanical energy (from the engine) into hydraulic energy (oil pressure), and then back into mechanical energy (cylinder movement). Unfortunately, in physics, there are no 100% efficient systems. Part of the energy always escapes as heat.
What heats the oil the most?
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Internal friction: Oil forced at high speed through narrow pipes and distributor crevices naturally heats up.
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Operating on the relief valve: If the machine is overloaded (e.g., the cylinder has reached its end, and you continue to hold the lever), the entire pump output "squeezes" through the safety valve back to the tank. This acts like a giant, mechanical kettle!
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Worn pump: Increased clearances inside the pump mean that some of the oil, instead of flowing into the system, churns inside the pump housing, generating extreme amounts of heat.
2. The deadly 80°C limit. What happens to overheated hydraulics?
The optimal operating temperature for most hydraulic systems is between 40°C and 60°C. When the temperature exceeds 80-90°C, a real drama begins in the system:
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Loss of viscosity (oil becomes like water): Heated oil becomes thin. The "lubricating film" disappears, meaning that metal parts inside the pump and distributor start to rub against each other dry. Thin oil also escapes more easily through any clearances, which directly explains why the machine loses strength and slows down.
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Seal death: As we wrote in previous articles, standard NBR rubber seals can withstand up to approx. 90°C. Above this value, they harden, become brittle, and start leaking oil from every cylinder and connection.
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Oil degradation: Overheated oil oxidizes faster. Lacquers and sludges precipitate from it, clogging filters and blocking precise spools in distributors.
3. Oil coolers – the first line of defense
In small systems, heat dissipation through the steel walls of the oil tank is sufficient. In heavy machinery (excavators, loaders, combines), this is not enough – a hydraulic oil cooler is essential.
Air coolers (aluminum radiator + fan) are the most popular. However, for the cooler to save your system, you must take care of it!
BRhydraulic Tip: Even the largest and most expensive cooler is useless if its fins are clogged with dust, chaff, or mud. Air cannot flow through it. Regularly blowing out the cooler with compressed air is the most important and cheapest service procedure! Also check if the thermostat correctly engages the fan (if it is electrically driven).
Summary
Temperature is a silent killer of power hydraulics. If your machine loses power after an hour of operation, do not accelerate and do not "push" it forcibly. Stop the equipment, check the tank temperature (if it burns your hand – it's bad!) and diagnose the problem. Perhaps the culprit is a dirty cooler, a blocked relief valve, or a dying pump.
