Rotary Cutter Why is mower gear box oil milky?

[CobyRupert]

7’ Frontier mower. I ran the mower for first time in 2 -3 months, THEN I decided to check the gearbox oil level (I know). Oil level was fine, but oil looks milky. How did water get in? Or has it always been there?

5 years ago, I changed the input shaft seal because, vent/filler bolt was plugged, and unvented it pushed oil out the input shaft seal (on hot days).
I’m pretty sure I drained most, if not all, of the oil out at that time with a suction hose, and refilled with new oil.

When I checked oil BEFORE the last time using it and before turning it on, oil level was fine and oil was clear. I’ve noticed no oil leaks outside of gearbox. Vent is working fine. I store mower outside but cover the gear box with a plastic John Deere garden cart.

Would oil get water just from the gearbox “breathing” through the vent over a period of months? Years? Could water be in gear box for years, but I don’t notice it at the beginning of the year when it’s not stirred up? And my dipstick only touches the top layers? I’m mystified.

 

[oldnslo]

Could be from condensation if live in an area with temperature swings and humidity.

 

[CobyRupert]

Could be from condensation if live in an area with temperature swings and humidity.

Has to be right? I wonder how come I’ve never noticed it in the 13 years I’ve owned it? It has to be because I check oil each season before I run it and stir it up? Now I’m curious to see if the oil and water separate over a few days and it goes back to looking like what I see each spring.

Any else have that much water accumulate through a breather?

 

[9973720wb19]

Moisture. Change it and check it regularly

 

[old and tired]

Any else have that much water accumulate through a breather?

I don't know if it comes through the breather... I've changed the oil twice in my Bush Hog RDTH72 twice in 20 years both times milky oil.

I don't worry about it since I never saw any rust what-so-ever. I do suck it dry when I change the oil. And the mower sits under a covered area out of the weather...

 

[zzvyb6]

The gearbox has some air in it. When it gets hot, the air expands, builds pressure and the air is leaked/exhausted out. When the machine cools, the air contracts and draws in outside (humid) air. The water vapor condenses into the hygroscopic (water vapor absorbing) oil and it becomes cloudy.

Minimized the air pocket and consider a grease or a non-hygroscopic oil for the gearbox content. Same for any machine with confined oil usage.
You might find that the oil is clear once the cutter is used hard and the gearbox heats up. The water boils off and out. If it really concerns you, make sure the gearbox is air-tight and put an oil trap on the gearbox breather. This provides for some temporary overflow, just like the burp bottle on a radiator.

 

[DutchInNZ]

The gearbox has some air in it. When it gets hot, the air expands, builds pressure and the air is leaked/exhausted out. When the machine cools, the air contracts and draws in outside (humid) air. The water vapor condenses into the hygroscopic (water vapor absorbing) oil and it becomes cloudy.

Minimized the air pocket and consider a grease or a non-hygroscopic oil for the gearbox content. Same for any machine with confined oil usage.
You might find that the oil is clear once the cutter is used hard and the gearbox heats up. The water boils off and out. If it really concerns you, make sure the gearbox is air-tight and put an oil trap on the gearbox breather. This provides for some temporary overflow, just like the burp bottle on a radiator.

If with "non-hygroscopic" you mean an oil without an emulsifier, I am not so sure that that would be so advisable. You will then get two separate layers of liquid in the gear box, the lowest one water and the upper one oil. Your gears might then pick up the water from the bottom and run with that as only lubricant. Emulsifiers are added to every gear and engine oil with the intention to prevent exactly that happening; an oil with emulsified water in it lubricates still a lot better than water alone.

Further, if you run gears, or anything that has a rubbing/sliding motion, the lubricant between the contact area of the teeth is rubbed away, be it grease or oil. In an oil bath the gears get continuously re-wet (re-wetted? re-liquidet?) with oil; running in grease does not re-wet. Bearings can run in grease because the innards are rolling with no friction whereas gear teeth are rubbing against each other, even with a parabolic cut.