Sycko, Your situation sounds very similar to my old log splitter, which had an 11gpm pump, 5 gal tank, and a 4" cylinder. It got noticeably hotter in warm weather.
I built a new larger splitter recently, it runs much cooler.
The two types of heat created in splitters are the heat of compression and frictional heat.
The heat of compression is the "work" being done by the cylinder.
Frictional heat is created by the friction encountered in the plumbing system.
A well plumbed system won't create as much frictional heat, a system with a lot of elbows, restrictions and undersized hoses will create more frictional heat.
When I designed the new splitter, I gave attention to the plumbing, always opting for the least amount of restriction, which means a little cooler running.
Heat of compression is caused by the cylinder doing work at a given pressure. I used a larger pump and larger diameter cylinder, so it doesn't have to work as hard, thus, the larger diameter cylinder can split a given log with less overall pressure (less heat created) than a smaller cylinder at higher pressures.
My initial thought is that a 30 ton unit shouldn't be running in High pressure stage that much, unelss you are splitting a very tough wood species.
If your oil filter is old, I'd advise changing it. They typically start bypassing at about 15 or 16psi, but that is enough to cause back-pressure that will also cause more frictional heating, even when no work is being down. The other thing to look at is the plumbing itself. if there are any restrictions, like undersized fittings, small diameter hoses, reducers, etc. you can replace them to make it a more free flowing system.
Example: a ran a short 3/4" hose into my filter housing, but then stepped it up to 1" from the Out port of the filter housing, going into the tank. The idea is trying to reduce backpressure and give it unrestricted flow back to the tank.
As people stated above, a hdyraulic system will run XX degrees above ambient temp, if you split when it's 80 degrees F outside, but normally are splitting when it's 40F outside, the oil could run up to another 40F warmer, just due to the rise in ambient temps.
All in all, my old splitter was the same as yours, got pretty warm, but not so hot you couldn't touch it. Mine was also an HF unit.
I used it for a long long time with no issues. It just ran fairly warm to the touch.
Which HF model is it?