Dearborn 19-21 Loader

This 8N we've talked about over the past 2 years. It is finally in working order (thank you all) but today I was using it for a short time to check out everything before putting the hood back on. After about 15 minutes of attacking a dirt pile the hydraulic oil began to squirt out the top filler hole. Some one had installed a nipple in the filler port, cut a groove in the top threads and installed a cap also with a groove in the threads to ???act as a vent??? That vent sprayed my noble body with hydraulic fluid and produced enough smoke hitting the exhaust pipe to spay for mosquitos! I included a picture which hopefully explains it better. I have the manuals for the loader and the hydraulic bucket which tells me there should be 5 gallons of fluid in the rig but can it be overfilled? The second picture should show a 1/4 inch plug in the left frame member about 1/3 of the way down which might be a place to check fluid level ???? but the manual doesn't address this nor does it say much about the top fillet plug. Can use all the help I can get - the hydraulic pump works fine and someone before me must have raided his pension fund to replace almost every hydraulic hose and cylinder seals.

In one of my loaders that uses the frame for a sump, I screwed a couple inches of pipe into that top port. pipe had threads on each end.

on the top of the pipe I used a nipple adapter so i could go to rubber hose. from there i used a cheap 1$ lawnmower gas filter into the rubber hose, then another short rubber hose ziptied to the pipe, aiming down.

it will breathe, but bugs and dirt can't get past the filter.

the pipe adds a bit of space for thermal expansion if you have it plumb full of fluid.

is the fluid creamy or foamy? might be sucking air at the pump

I think the fluid might be a little foamy and definitely a possibility which I'll check - the hydraulics are working a little slow - just maybe. But I have a feeling that the darn thing is just overfilled which is why I keep coming back to that 1/4 inch plug on the side of the frame. This isn't just a few squirts - my shirt is soaking with fluid. Somebody has to have had this problem before. I like Soundguys idea of the hydraulic expansion pipe and the overflow line with a filter, but until I solve this massive outflow problem I can't do anything. At this point I'm tempted to: (1) Open the 1/4 inch plug and drain to that level and if that doesn't work (2) drain all the fluid and put back the measured amount.

Water = overfilled, and when heated and under hyd pressure, water turns to steam, foams and can make sump spill over

Water makes sense because this was a lost cause I found in a storage area and beside being a "Mutt" 49 body and 51 engine it was a "restoration" somebody gave up on. I will drain the entire system in the next few days and see what comes out, Still open to anybody who has other ideas. I'll post the drain results in the next week or two. Thanks Guys

sure, could be overfilled, it needs a little room in there.
(if any cylinders were extended at all and you filled it to the top, when the cylinder fully retracts, it has to go somewhere)

I have a Farmall (small reservoir) that I have added this and that to.
I did as Soundguy said and added a pipefitting vent with hose routed down under. It finds the reservoir fluid level it prefers pretty quickly in use.

I have a Dearborn 19-61. When mine did as yours is doing what I found out was air was being sucked in thru the drain plug, however I didn't figure it out till after the pump grenaded.
It wouldn't push fluid out even when hot but would suck air in.
I used teflon tape to seal drain plug and no more foaming.
I also replaced the original Parker controller as was plumb wore out.
I too like soundguy's filter idea as mine builds pressure during use.