Filter back pressure

[6sunset6]

I have a rather long post in "build it yourself" about a log splitter. But the question I have is better asked here.
16 gpm pump 18 gal res BIG Filter in the return line Wix 51759 30gpm 10u paper element spin on.
Iso 46 hyd oil around 40d F outside

When I start up the pump the filter is in bypass 25psi and after a bit it drops to zero or close to it. Temperature gage on the res has not even moved after an hour of running.

Question is why does the filter bypass for maybe 10-15 min?

 

[J_J]

Perhaps the thick cold oil will not pass through as well as when warm and a little thinner.

 

[oldnslo]

+1 on what JJ said. ISO 46 at 40 degrees is kind of thick and after operating for a few minutes the oil in the element starts flowing and your gauge drops. Pretty typical for a cool/cold weather start.

 

[J_J]

If you want to heat up the tank fluid, hold the valve in extended operation until the fluid is warm. You really don't want the filter to bypass for very long. The relief will pass fluid as long as you hold the lever.