like rod says, check your cooling system.
on forklifts the radiator is mounted near the rear of the truck, the engine is mounted backwards to what most would think so the radiator is mounted towards the rear of the truck. Raise the hood and check your resivoir and remove the radiator cap and check the level in the radiator. Also check your hoses, waterpump for leaks. You'll need a pressure tester if you want to do this without getting the engine hot. OR you can just run the lift and watch for where it is leaking at. Remember, where there is steam there is a leak and most certainly the coolant level is low.

thats a little vague of a description , steam would possibly indicate a coolant leak.have you checked your coolant level.