The pumps on your Ariens/Gravely pressure washer have a thermal relief valve feature to help alleviate heat build-up, but this feature does not completely cool the pump. Please read the explanation below:
Proper cooling of the pump relies on the unrestricted flow of water through it. This only happens when the wand trigger is depressed and it is spraying. During the idle mode, the water is only circulated beneath the head of the pump, and proper cooling does not take place. If the unit is left idling for 15 minutes or longer, it can cause the pump to overheat.
Note: The thermal relief valve will only discharge the recirclulating water beneath the pump head. This happens when it reaches 104 degrees fahrenheit.
Important: Overheating results in the oil breaking down, which could cause excessive wear inside the pump. Internal seals may melt, resulting in oil and/or water leak. If overheating is noticed, take the unit to a local Gravely dealer to change the oil, inspect/replace the seals, and test the thermal relief valve.