Overheating is one of the 2 most common causes of hydraulic system failure (the other is contamination).
How hot is too hot? If the reservoir is so hot you can’t hold your hand on it, it’s probably too hot. 150°F is as hot as we recommend for the reservoir. At that temperature one or more of your components is likely much hotter. Most seals start to lose elasticity at 180°F. Some components in the oil may start to break down. And the oil gets so thin at high temps that it doesn’t lubricate the moving metal parts sufficiently.
What makes it overheat? Friction in the pump, and internal leakage in pump, valve, or cylinder all create some heat. Also the power needed to push the oil through various holes and passages in valve, hoses & fittings makes it hotter. It often only takes 15 – 20 minutes for the heat to build up. Hydraulic motors running constantly usually create a lot of heat.
Where does the heat go? The heat is radiated away mostly by the metal components. While the oil not being used at the moment sits in the reservoir, it has a chance to cool through the walls of the tank. The longer it rests in the tank, the more chance it has to cool off.
