well i can see it being between the full and add sight glasses as being a good level but if it is in the 'add' sight glass then in my mind that means add fluid. AND... if the upper sight glass is the full mark then one would think to fill it to that level but not above.
And yes i know about JLG's engineers, they are a knarly bunch and no they do not like being questioned , in fact they can get right testy about it LoL...

any how... just draining out some of the oil so the level is lower than the 'full' mark (sight glass) should fix the problem.
:o)

OK LOL. I went back rechecked all possible causes checked hoses and fittings even took pressure readings all ok. after a few more calls to JLG. the guy (Alan) started reading from the book. it says to cycle all functions completely lift, steering 1 time and then check fluid level. it states fluid should never be in the upper (full) sight plug. and should only be half in the lower sight plug (add).
goes against everthing you have ever been taught. So going by that someone at the school added fluid. no one admits to it.Lol per Alan cause he had no reason for this just starting to happen after years of service. He also didn't like being questioned. LOL nut damm*t i would like to have found out more of a reason than that. So in the end when your JLG is in the add bubble leave it alone and made sure all functions work.??? no need for sight glasses. Heck just remove them and add plugs. sorry just venting alittle

yeah i understand your situation
i am like that too, not knowing what is causing a problem just gets to me sometimes and i really hate doing work-a-round fixes without knowing what the real problem is.

it is strange though that with the oil level at normal levels that the oil is finding its way into the breather cap. We have covered all the possibilities that may cause that so it has to be something you can't see. And from the looks of that tank assembly its not very easy to see inside of it anyway, only 2 places to look, the breather cap hole or the fill cap nozzle according to the diagram i saw from JLG on the hydraulic tank.
It still comes to mind that somehow the oil level is getting high enough for it to enter that cap nozzle. Maybe the force from the returning fluid is making it swell inside where you cant see it, but that doesn't seem logical either because of where the supply/return line is but i have seen stranger things before.

honestly without being able to get in front of it and see what is going on i am just throwing out educated guesses anyway.
I wish you luck and hope you do find out why it is happening.
If you do please come back and post what you find, i am very curious myself to know :o)

have a great july 4th

LOL...yeah that is what i was thinking of doing. but at the same time would like to have found a issue with it. the unit has been there for awhile so not really thinking its a tank problem or sight glass location issue. Hey.. Thanks for the thoughts.I will post back if i come up with something else so we all know for the future.
as for now i just broke the fan idler pully on a mits fgc15. not the easiest to get to in the first place.. it happens i guess.

only other suggestion i can give is to just drain out some of the oil.

as long as it is near the full sight glass there should be plenty of oil to operate the lift.

i had a similar problem with a combi lift and turns out the mfg put the sight glass in the wrong location on the tank when it was made.
i had 2 choices, replace the tank with a new one or just let some of the oil out till it stopped coming out of the breather.

that would be the simpilist solution imo :o)

yes i have done that. I can operate the hyd's at the ground control box which is right in front of the hyd tank. And all looks normal in the tank. Up until it pukes out. No foam no air bubbles not alot of splash. guess that is what has me stumped

may be an in-tank defleftor come loose or...
maybe an internal strainer on return line that come off?
too much return pressure...

get someone else to operate it... remove cap and watch inside when they lower it and see whats going on.
may give you a better idea on whats happening in there

yes filter has been changed. Fluid level checked at operating temp.
That is what the guy from JLG kept talking about. outside temp. as its been rather cool in Indiana so far this year. The fluid starts out at the bottom of the add sight glass. when i arrive at the location. does not seem to matter if its hot or cold. when lowering will spill over from breather cap. like i said while operating the fluid does not get foamy and it goes up smoothly. same when lowering. What could be in the tank?. this unit is at a high school and no else works on it and they don't add fluid of any kind

coming out of the breather cap right?
when you're checking the oil levels are you doing it with the unit hot or cold?
it should be done with the oil at operating temp only.
If you are checking it when the oil is cold and adding it to get it to the top glass then when it gets hot it is probably expanding alot and making it overfull.

Try checking it the way i said, drain out some if it is overfull when hot till you see it at the lower hemisphere of the upper sight glass, not above that. Also clean out the breather cap since it has oil in it, use a fast drying cleaner like electric motor or contact cleaner so it will not damage the element inside it.
Then come back and tell is if there is any difference?
If it is still forcing fluid out of the breather cap when lowering then there is something wrong inside the tank.

Hello Adam, I don't have any experience with JLG but some forklift manufactures use the same oil level indicator for different masts heights witch isn't correct. can you ask JLG what the total amount of oil it must be and start from there? what about oil temperature? is it happening also when the temperature is cold? These are just some ideas.
Regards
Marcb

Have you tried replacing filter