My Clark C500 HY 70 is having major hydraulic problems. I just restored the truck that had been sitting up for more than a year. However, I did not do anything to the hydraulic system at all. I was using the truck as normal & noticed a sudden strain on the engine & lost function of my hydraulics. It's almost as tho the engine is strained bc the hydraulic system is asking for pressure all the time. The fluid was very milky so I pumped the fluid out, cleaned the tank, changed the hydraulic filter in the tank, added all new oil & 1 gallon off lucas hydraulic conditioner. When I cranked it back up the engine still sounds strained. I was able to rev the engine all the way & get the hydraulics to work but it's obviously pressurizing my tank bc it blew the breather/dipstick out & covered the truck with oil. I'm thinking I either have a stuck pressure relief valve, plugged return hose, or stuck part in my valve body. Any help would be much appreciated.
The C500's are junk. The parts are so expensive it's like owning a Mercedes Benz. This is by far the most expensive old forklift to own. That said, I believe you hit the nail on the head. From my experience, you pressure relief valve has a broken spring, allowing all of the pressure to be returned to the tank. On some models the pressure relief is part of the hydraulic pump though. Just pray that lift cylinder never starts leaking, it's an expensive repair, has to be sent to a hydraulic shop for rebuild with more expensive parts. Good luck, let us know what you found out.