What Is Oil Cooling?
Oil cooling is the removal of heat from the oil circulating in a machine through a cooler, so that the oil stays within a suitable working temperature range. This article explains why oil heats up, how temperature affects the oil and how an air-oil cooler works.
Why does oil heat up?
Oil does more than lubricate; in the system it also acts as a heat carrier. Friction, flow resistance and mechanical losses turn energy into heat, and that heat passes into the oil. As the oil circulates, it carries heat from one place to another.
When the ambient temperature is high or the machine runs hard for a long time, the oil cannot shed heat sufficiently on its own. Its temperature rises step by step. This is the point where a separate cooler becomes necessary.
Temperature and viscosity
Viscosity is the oil's resistance to flow. As oil heats up it thins, which means its viscosity drops. Oil that becomes too thin may not form a sufficiently protective film between moving parts. Excessive temperature can also speed up the oxidation and aging of the oil.
For this reason every oil and every system has a suitable working temperature range. For that range, rely on the values from the machine and oil manufacturer.
Cooling does not mean keeping the oil as cold as possible. Oil that is too cold also thickens and struggles to flow on a cold start. The goal is to protect the oil both from overheating during operation and from needless cooling, in other words to keep it within the manufacturer's range.
Heat affects not only the oil itself but also the components that work with it. Pumps, valves, cylinders and bearings depend directly on the oil temperature. Oil temperature is therefore one of the indicators worth monitoring for the overall health of the machine.
The logic of an air-oil cooler
In an air-oil cooler, hot oil passes through channels or a finned coil. Air flowing from outside takes the heat from these surfaces. The oil and the air do not mix; only a metal wall separates them.
Airflow can be provided in two ways:
- Without a fan: Airflow comes from the machine's own fan or from the surroundings.
- Fan-cooled: A fan integrated into the cooler blows air over the fins. It does not depend on the machine's own airflow.
Safkan's fan-cooled oil cooler series is of this second type; for details, see the fan-cooled radiators page.
Which systems use it?
- Hydraulic systems and hydraulic power units
- Screw-type air compressors
- Transmission and torque converter circuits
- Construction machinery and forklifts
You can find the oil cooling application for compressors on the compressor radiators page. On the hydraulic side, you can read where the heat comes from in the article cooling in hydraulic systems and how radiators work.
How it differs from oil-water cooling
Oil can also be cooled with water instead of air. In oil-water coolers the heat is transferred to a cooling water circuit; this solution can be considered in fixed installations that have a water source and circuit. Air-oil coolers, on the other hand, do not need a separate water circuit, so they are common on mobile machines and machines working in the field. Which one is suitable depends on the facilities at the site and on the heat load.
Is oil cooling the same as engine cooling?
No. Engine cooling removes the heat of the engine block and cylinders with coolant. Oil cooling focuses on the temperature of the oil itself and is connected to a separate oil line, such as a hydraulic circuit, a compressor oil circuit or transmission oil. A machine may have both, and one does not replace the other.
Next step
To tell whether oil temperature is a problem in a system, first compare the working temperature with the manufacturer's limits. For the technical information you need to choose a cooler, you can write to us through the contact page.