bbforks;
To answer the question. The Optimum series truck has a somewhat marginal cooling system. It is often in need of TLC and "maintenance" to assist in the reduction of overheating issues.
To date the most unusual cause of an overheating engine that I have run across, has been replacement of a +400.00 USD that had restricted cores. To date I have had 62 different causes for overheating in LPG power units of industrial forklifts. If you are new at working with forklifts, some important facts to keep in your thoughts are 40% of heat waste from the engine is removed through the engines walls. The cooling air flow is from the floor, up through the radiator and out the tail weight. The smaller the openning in the tail weight the less air will flow.
In this discussion it's menione to watch for a surge in water flow when the thermostat opens and also to remove the thermostat. The H25 Nissan has a bottom by-pass thermostat, whose purpose is to create a mor even temperature between the engine's bottom and top plus determine the coolant flow direction with the engine temperature. Removal of a thermostat causes hot spots around the number 3 and 4 cylinders which could lead to cylinder wall scuffing and/or scoreing.
The thought I keep having is, Greg dealing with an engine that is operationally sound and is it governed correctly? Also, if he elects to remove the transmission for repair I should think it may be wise to find out if the trans pump and 3 packs need repair of replacement.
Greg, a normal and well tuned H25 hydraulic stall reading will be from 2000 to 2450 RPM. The trans in your forklift is a four element two stage (2 stator) torque convertor. The radiator which you replaced, does it have a part number 21460-86180? If the radiator number is different, I would question. It is an in-line 4 tube with serpintine metal fins designed for excellent cooling capabilities.