8HP 24Ton Wood Splitter Problem

I've been burning wood for some time now using it to heat my home. I cut Oak, Blackjack, Hickory, and Pecan to burn in my fireplace and usually heat it with around 5 ricks a year using a Regency wood stove.

So far I've always split my wood by maul but after hearing from folks owning hydraulic splitters I bought a used wood splitter claimed to be 8 years old but rarely used. After a little tinkering I got the motor running great and set my first log to Split. It was a 18" diameter freshly cut oak that the splitter made quick work of. After splitting 3 or 4 logs in this fashion I was thoroughly impressed with the power and ease of the splitter however it seemed to be losing strength. When the wedge contacts the wood I can audibly hear the gas motor working under the pressure but the wedge doesn't seem to be pressing very hard. I became discouraged and shut the unit down for lunch. Upon returning after a bit the wood splitter began splitting with ease again before eventually loosing power. The only thing that changes from the initial start to 10 minutes into the splitting session is the temperature of the hydraulic fluid which is warm in the hoses but obviously more viscous than at initial start.

My question is this... I'm assuming there is a hydraulic leak in the controller or the pump is going bad but how would I know which one to start with? My thoughts are that as the hydraulic fluid warms up it is either slipping through the controller (no leaks detected) or the pump is having problems moving it since its more fluid.

Any help would be appreciated as this is my first hydraulic endeavor.

(just for info I left the motor running with the controller in neutral for 30 minutes. The splitter then couldn't split a branch 4" in diameter and 18" long so that should give you some idea of the pressure loss)

Thanks for moving this to the proper forum. I apologize for my ineptitude. I did also want to mention that I bought the splitter for $500 and after replacing gas lines and cleaning the carb, needles, float, pump, and replacing the filter I'm at a total of $519 invested. Pretty sure its a $1500 splitter if I can get the hydraulics figured out.

I will change the hydraulic fluid and filter since that is the easiest option at the moment. I don't have a pressure gauge but will start that route next. I'll keep you posted. Thanks.

I replaced the fluid but that didn't help. I still don't think its operating as it should but its much much better.

Finally got around to working on the splitter over christmas break. replaced the hydraulic lines and now I'm back in business. All I can figure is that whichever hose was being placed under a vaccume was leaking air which was causing the loss in power. Ran the splitter for a while and it seems to be back in great shape. Also learned that it has to be sitting pretty level. During one use it quit and wouldn't start. After cool down it started then died after a few minutes. Apparently there is a low oil sensor that was losing oil when it ran but allowed it to start after all the oil had drained back down. It wasn't really that low but the unlevel ground wasn't helping. After moving it around I found that the vent on the hydraulic fluid couldn't be facing down either or it would leak hydraulic fluid down after it was warmed up and thoroughly expanded from the heat.

Thanks for all the help.