Note: There is a difference between "flow" and "pressure." Both must be correct in order for your hydraulic system to operate properly! Knowing one or the other may give an insight as to the condition of the system but you may need to determine both to have enough information to diagnose a problem. Pressure is a measure of the resistance created by the pump and controlled by the pressure regulator in the control valve. A system may have adequate pressure but may not operate a winch motor or cylinder properly due to flow. Flow is a measure of the volume of oil pumped through the system. A system may have adequate flow but may not operate a winch or cylinder properly due to pressure. Check the pressure by plumbing a guage into the pressure line fom the pump using a tee type fitting. The guage will then read the pressure as the control valve is operated. If a funtion is topped out (such as the what occurs when a circuit containing a cylinder is run until the cylinder is fully retracted or extended) the maximum pressure can be read. The relief valve can then be adjusted to achieve the desired pressure. The flow of the sytem can be checked by using a flow meter. This is a more expensive piece of test equipment but will measure both flow and pressure. It will also allow you to read the flow at various pressures via a mechanism contained in the meter. Typically one would check the pressure first because most pumps will show low pressures at low RPM's if worn. If the pressure raises as RPM's are increased the indication is that the pump is worn but could possibly perform satisfatorily at higher RPM's. If the pressure raises as PRM's are increased but you are unable to reach the desired pressure at acceptable RPM's then the pump should be replaced. Refer to your operators manual for the correct pressure for the make and model. Or call Zip's for help at 1-800-222-6047.
If it is very cold out (10 degrees or below) there is probably nothing broken. It is likely that the low temperatures have caused the oil to thicken to the point it will not draw sufficiently from the reservoir. The noise that you hear is caused by "cavitation" and can quickly ruin a pump as the pump starves for oil. The problem can be remedied by draining the system and replacing the fluid with a Synthetic Hydraulic oil with a very low pour point. Zip's stocks this type of oil in 5 gallon quatities. Check our E-store for H-T Super HD-5 Syntetic Hydraulic Oil or the non-synthetic Talamar Extreme which has a -50 degree pour point. In warm weather pump noise may indicate that the suction line is restricted. Be sure to determine if the noise is actually coming form the pump or if it is coming from the power take-off (PTO). Some times it is hard to tell without removing the pump.
Not necessarily. More often than not poor performance of a winch has to do with the hydraulic system performance. Check the pressure and flow first. If either is too low the winch will stall under load. If these are as they should be only then would I suspect the winch motor. Be sure to check the winch for proper lubrication. It may pay to pull the drain plug for a quick check to see if filings or debris have accumulated. This would indicate a worm or bearing failure. Most winches use a 80/90 weight gear lube and should be filled to the check plug found on the side of the winch. Over filling ill cause oil to rin out around the output shaft.