How to prevent overheating The usual method is by using a large enough reservoir. That does 2 things: it gives the oil time to rest and give off its heat. And the larger metal surfaces radiate more heat.
How big a tank do I need? The rule of thumb is one minute’s pump flow as a bare minimum, i.e., if the pump flow is 16 GPM, the tank should hold no less than 16 gallons. More is better! Industrial systems often use 3 minute’s worth of oil. A heat exchanger is the other option. Systems which will only be run for a short time, 15 minutes or less, and then allowed to cool, can use much smaller tanks. Remember, your system doesn’t care if you have a good reason why you can’t install a larger tank! If it gets too hot, you will pay!