Overheating problems can come from two areas:
The cooling circuit or the hydraulic system.
If the indications are that the cooling circuit is functioning satisfactorily but the system is overheating – then we need to locate the source of the ‘abnormal’ heat load.
When fluid moves from a high pressure zone to a low pressure zone we call this pressure drop.
When a pressure drop occurs WITHOUT useful work, heat is generated. For example, the pressure drop across the ports of a properly functioning motor produces torque at the motor’s drive shaft and ultimately useful work.
On the other hand, the pressure drop across a relief valve doesn’t produce any work, so this energy is converted to heat – which is an undesirable heat load on the system.
Because a pressure drop without useful work creates heat, an infra-red thermometer can often be used as a quick and effective means of locating abnormal heat load.
For example, if oil is passing over a relief valve, the localized heat generation means this component will be hotter than the rest of the system.