You're getting a lot of hearsay information, and just plain "old wives tales", which I find common in fields in which most people have little training or experience.
First, how hot is too hot? At 180 degrees, Buna (nitrile rubber) seals start to break down - they lose their elasticity - get hard & brittle. A good running temp is 140-150. A rule of thumb is: if it's too hot to hold your hand on it, it's too hot. Oil viscosity gets too low and friction increases dramatically.
Well it is too hot then. After 30min I can not touch the cylinder.
Causes of overheating:
The oil: ATF is good in cold weather because it has a low pour point, and will flow easily into the pump even on start-up. It's not recommended in warmer weather, because it thins out too much and doesn't lubricate the fast moving metal parts in the pump, thus causing lots of heat from friction. 10 wt motor oil is good in warmer weather - it lubricates well and can take the heat. We use it in our shop testers and have no problems with foaming or anything else. (the detergent in motor oils keeps dirt in suspension, it doesn't foam. It's not dish detergent, which has a foaming additive for the housewives' benefit.)
Cheap tractor store oil is a common cause of overheating.
The ATF is dextron III. Northern says to use ATF at temps over 70*. If changing the ATF out would fix the problem I would but I know of other people who run ATF year around with no problems. If I could do it over I would use 10wt oil but now I already have $75 in ATF
The tank: for industrial systems we recommend 3 minute's worth of oil in the reservoir. Never less than one minute's oil. (Your tank is pretty small).
True. Thanks Northern.
The lines & fittings: 16 GPM is generally the maximum for 1/2" lines, that is, it takes quite a bit of power to push the oil through the lines. All that power is wasted, and is returned to you as heat. The more fittings and other components, like check valves, in the line, the bigger it needs to be. Other components, like the directional valve, also need to be sized for the flow. Using all of them to their maximum capacity is just asking for a heat problem. It's like driving your car at 100 MPH - it will probably do it, but there will be more problems.
The valve has 3/4 in/out ports and 1/2in working ports. The oil will still get hot with the valve open so I'm thinking the valve should be flowing enough. If I call Northern they will say the out let of the pump is 1/2in so that is big enough.
The cylinder: if there is internal leakage in the cylinder, it will generate heat. Sometimes you can feel it on the cylinder barrel. Leaky piston seals will cause this. You can test this by fully extending the cylinder, removing the rod end hose, and trying to extend the cylinder again. WEAR YOUR SAFETY GLASSES! If the piston is leaking, oil will come out the open cylinder port when the rod is not moving. If it doesn't, the cylinder is OK. It won't hurt the cylinder to run it against the end. (By the way, iron piston rings always leak a little, and are almost never found on mobile equipment, just a few industrial applications which don't have to hold solidly.)
With the system getting just as hot without useing the ram I don't think the cylinder is leaking. I also did the come-along trick posted earler with out finding anything.
Now, your system: I assume you're not trying to run both pumps at once. That would really be too much flow.
Air in the oil might cause heat, but it would also cause the pump to whine a lot - a loud, irritating noise which is hard to miss. The same if the intake hose collapsed.
I think you're probably suffering from a combination of most of the problems described above. A larger tank might be enough to help, but probably not with all the 1/2" hoses & fittings. The check valves are a good idea to protect the non-running pump, but they will also add to the heat. You could put a couple full-bore ball valves in, and close the one to the pump you're not using. (They have to be high pressure ball valves.)
I don't know what kind of directional valve you have, but it may be undersized for the flow too. Undersized components are cheaper and so are common on cheaper equipment. Inexperienced technical service reps are cheaper too!
A pressure gauge installed between the pump & valve would tell how much it takes just to circulate your oil. 100 PSI or less would be good. It could also tell if any changes you make have helped reduce the pressure.
If you have any other thoughts or questions, just email me:
[email protected]
:newbie: :rockn: :hmm3grin2orange: 
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