Engine Oil Leak

1989 L785 with ~7,800 hours

Recently developed a leak on my NH L785.

Found leak evidence around the oil pan gasket with most concentrated at the rear of the engine.

Replaced the oil pan gasket which significantly reduced the amount of oil being lost.

But still have a leak where the engine/hydraulic pump connect.

As it is appears to be fresh oil, from the replacement of the gasket, I am assuming it is the rear main seal.
- Not a steady stream, but several drips per minute (see attached) my guess would be about a quart of oil per day. So nothing I cannot manage for the time being.

Machine uses 10-30 for hydraulic fluid, COULD there be a leak in the hydraulic system that I am just not seeing, any recommendations on how to further isolate the leak?

ONLY leaks when running, ie shut down, leak stops relatively quickly.

It appears no one has ever been in this engine before.

The engine DOES have some blow by pressure in the oil pan, BUT, i added a pressure relief fitting/filter in the unused dipstick port to relieve pressure buildup which helped also.

If consensus is rear main seal is culprit, I will likely baby the machine for this summer (to many projects to get done) and then do a complete rebuild on the engine over winter, to account for the engine blow by AND the rear main seal at the same time.

If there is a leak source I am overlooking, I will try to locate them immediately.

Thank you in advance for any/all support/thoughts.

You said it is where the engine and hydro connects, is it Hydraulic Oil then its the input shaft sela from the hydrostatic pump, if its engine oil its the rear main seal from the engine.

FWC, Thank you, is there an easy way to differentiate between the two possible sources?

add some oil dye to one or the other and see if it shows up leaking out! they sell it at most larger chain auto parts stores!

Thank you, completely forgot about oil dyes.

Feeling a little foolish.

if there is no fluid loss in your hydro system and loss in the engine oil,well it is the engine oil.

mrbb said:

add some oil dye to one or the other and see if it shows up leaking out! they sell it at most larger chain auto parts stores!

Click to expand...

Well unless he just did a oil change, you should be able to tell if its hydraulic oil or engine oil without any dye.

fortworth-cowboy said:

Well unless he just did a oil change, you should be able to tell if its hydraulic oil or engine oil without any dye.

Click to expand...

well on many of these older machines, they use Motor oil in both systems(10w/30) , motor/engine, pending what one prefers to call it,(HAHA) and hydraulic system,
so fluid leaking would be the same, minus if you added dye to one,. t ?
NOW< if someone altered things and started using Hydraulic fluid in it over what the OEM calls for, well, then?? yes, I think there should be a difference in smell and color or??
BUT again, adding dye, will also, make this easier on folks that don't know the differences or experience id' ing them by sight/smell in its original form! !

FWC, MRBB,

Thank you for all the help and support.

This machine does use 10-30 as hydraulic fluid and it is clean.

Verified it is hydraulic fluid, BUT, it is coming from under the pump and running back to the area under the rear of the engine.

Leak finally got bad enough I can now see the oil flowing, cannot see the leak, as it is up under the pump.

Now I am trying to find videos on how to access that area, so far have not found much.

Appears the only way to go is pulling the pump out.

Again, thank you for the help!!!

I am not familiar with the L785.
On my Lx865, I found the bolts holding the pump to the drive housing loose, pumps leaking oil at the input shaft seals, & the rear engine support bushing/rubber mount deteriorated/squashed, so the pump was rubbing against the frame ( had actually rubbed a hole in the frame, but not the pump yet)
On my machine service manual instructed on how to tip the cab to get access, but tool no longer available. I ended up fabricating the tool. Good Luck. CE