The first thing everyone suggested was to check the safety relief valve. They lowered the relief until they heard and felt the valve relieving. They then increased the valve's pressure setting until the noise and vibration settled down. The heating problem persisted. They then replaced the heat exchanger to no avail.

They called their local hydraulic distributor, and the technician simply asked them if the return line from the 5-psi check valve going back to the tank was hot. It was. They determined that the contractor who put the new pump in had installed the ½-psi check in backwards, causing the original overheating problem since the case drain flowed directly to tank.

Congratulations to Richard McAfee, CFPE, at Texas Hydraulics, whose name was chosen at random from those who correctly answered November's Troubleshooting Challenge. A $50 gift card is in the mail to him.