Is there a way to valve off the hydraulic load at the pumps for easier starting in colder months?
That's a very good question.
Let's discuss the 400 series.
There are two PTO pumps.
Main PTO pump.
AUX PTO/steering/FEL pump.
It's my understanding the main PTO pump just pumps right through the soleniod block and back into the tank until you flip the dash switch, then it pumps through the ports on the FEL arms. So, its about as bypassed as you can get already.
The AUX PTO/steering/FEL pump pumps through the steering valve, out the power-beyond port, through the FEL valve body and back into the tank. Those valves are open center, so don't know how my resistance they offer. You could certainly put a diverter valve right after the output of that pump and send the fluid directly back to the tank. That would take most pressure off of that circuit.
Now for the variable volume tram pump. When your foot is off the treadle, the swash plate is neutral and the gas motor is just spinning the plate in the fluid inside the pump. There really is no way to bypass that. I'm sure its thick fluid when its cold. Again, as I understand it, the only time the tram pump draws fluid from the tank is for the makeup section. For the most part, the tram circuit is a closed loop and only needs to replace fluid leaked past the tram pump. As long as you have the treadle in the neutral position there is not load going through the wheel motors. The only way to bypass the tram pump would be to put it on a clutch.
I think the first and best option to reduce load on startup would be running synthetic variable viscosity oil in the engine and hydraulic system.
My second choice would be to put a selector valve in the AUX PTO/steering/fel circuit to bypass the valve and go directly back to the tank.
The first choice would require zero mechanical mods and would cost the price of two quarts of synthetic for the engine and 40 quarts for the hydraulics.
The second choice would cost the price of the valve (about a hundred bucks here:
Selector Valves ) plus the price of a hose and a T or Y to tap into the return to the tank.
I switched my engine to 5w30 Mobil1 at my first oil change and at every 50 hour filter change I top off with the same oil in my hydraulic tank. So, I've got about 9 qys of diluted synthetic in there by now.