Oil Top-Ups and Larger Gearboxes

I would venture to guess that since an internal combustion engine is required to have a precise amount of air volume inside, that may be the reasoning for that idea. It should never be overfilled, but we all seem to know that. If I were to check an engine (shut off after some operation) and find it a "quart" low on oil, I would be hesitant to pour an entire quart of oil into it. I prefer to add a pint or so, operate it a few minutes, and check again. The engine may not be as low on oil as its dipstick indicates. Is this "10%" idea an axiom for lubrication? Wow, I never heard of it until now.

For a gearbox such as a large reducer, I think it would depend on the method of checking the oil level. If it has but a common sight glass mounted on the gearcase, then it may well be full or overfilled and indicate a low oil level while in operation. This is usually due to a sight glass being too close to an in-running gear that is sucking oil away from the point of inspection. For large circulating systems this is usally not the case, as the sight glass is placed on the main reservoir and away from the spinning gears.

The total oil capacity and quantity of a gearbox is usually determined by the manufacturer, and unless there is sufficient plumbing and an accompanying reservoir the oil level must be verified when the gearbox is not in motion. The gearbox also needs a certain amount of air volume vs. oil volume to dissapate heat, and this is usually in the design by the manufacturer.

You have me interested with this seemingly simple subject and I hope someone elaborates about the reasoning behind the "10% at a time" method.

Best Regards,

Ing. Robert Forbus

Dear Robert,

This maximum 10% oil top-up at a time(Mostly while running condition) was recommended by a I C Engine manufacturer and Moreover on the dipstick running/idle engine sump levels(Minimum/maximum) were mentioned.

If large quantity of oil leaked from a sump, is it possible to top-up the desired quantity of oil ?

In more than 200 ltrs of oil capacity sump it is possible to top-up a certain quantity of oil to maintain the MTBF(mean time between failure). incase of degraded oil condition ?

Is there any specific reasons behind this procedure?

Is this specific procedure contextual to your to the generality of you question?

If the answer is yes. Than, it is applicable for the gearboxes of bigger size?

No.