The constant oil flow required to operate the hyd. powered tools causes the hyd. fluid to heat up, the standard models do not have the oil cooling systems necessary to keep the oil temperature from getting hot enough to damage the seals in the transmission as well as cause other trans. problems. As the trans oil heats up it tends to thin out lessening it's ability to provide proper lubrication to the trans.
The turf utility and the work site utility come with a a second valve that has it's own oil reservoir as well as a hyd. cooler and cooling fan to control the oil temp.