heat · Medium
Hydraulic oil runs hot
Heat is a symptom of lost energy, and in hydraulics lost energy is a leak — usually an internal one. The oil cooler is the last suspect, not the first, and it is the one everybody replaces first.
What it usually is
| Share of cases | Cause and how to check it |
|---|---|
| 38% | Internal leakage in motors or pump (worn groups) Case-drain flow on each motor and the pump. One hot circuit narrows the search to one unit. |
| 26% | Cooler blocked or fan / hydraulic-driven fan weak Infrared the cooler inlet and outlet: a working cooler drops 10 °C or more across. |
| 20% | A relief valve blowing continuously Watch pressure at idle with no function commanded — it should be standby, not relief. |
| 16% | Wrong oil grade or contaminated oil Viscosity at 40 °C and water content; a 10 °C ambient swing needs a different grade. |
Field tests
1. Temperature map
An infrared camera on the tank, each motor housing and the valve block after 30 minutes of work. The hot unit names itself.
2. Case drain again
Heat and case drain are the same measurement seen two ways.
3. Oil sample
A 100 ml sample sent for water, viscosity and particle count answers three causes at once.
What actually fixes it
Overheating is usually a repair-kit conversation, not an assembly conversation — which is why it is worth diagnosing before ordering.
Send the plate, get the variant in writing.
One photo of the nameplate and one of the pump from the side. We confirm the variant, then quote — the price holds for seven days.