Air bubbles in oil

[Diver Down]

While underway today I checked the oil levels in both transmissions. Both were at the full mark and the oil is clean. However, the fluid on the dipstick in one tranny appears 'bubbly' (dense, carbonated look). The pressure is fine (135 psi) and the oil is not emulsified, i.e. there is no water in the oil. Have any of you seen this condition or have an opinion about what's going on?

[Nonchalant1]

No problem. I have had this for 7,000 miles (Allison M20s). Sometimes one does it sometimes both. I'd say nothing to worry about.

Doug

[Sonny]

Both boats i ran with allisons had bubbly oil

[Genesis]

May be (probably is) an air leak in the suction side. Check the gasket at the intake strainer.

This assumes the level is ok.

[jlightonjr]

We had 671ti's with Capitals the Stbd trans oil would bubble the Port would not... I don't think it is a problem as long as you check/change the trans oil per the requirements and keep a close eye on it.

[REBrueckner]

I thought transmission oil levels were to be checked at idle neutral...is that correct or not?

Is there anything that would cause such bubbling in gear versus neutral?? Is it sensitive to RPM?

I'd hate the thought of bubbly oil in a transmission....just doesn't seem right.

I like Genesis suggestion.

I've never checked mine underway....just what I needed, something else to worry about.....

[Diver Down]

Rob, I believe you are correct and I did check the fluid levels while idling in neutral. I guess the comment about 'underway' was not necessary... I just wasn't dockside. The bubbling does seem peculiar but there are no obvious problems otherwise.

[MikeP]

Bubbles in engine or tranny oil can be caused both by oil too low or oil too high. Used to see car engines do this quite frequently because of too much oil.

Too low can cause air to be sucked in with the oil - very bad. Too high can cause the oil to be beaten into froth by rotating parts - not good but not as bad because it occurs AFTER the oil is pumped through the system, not before so there is no danger of insufficient oil for system lubrication. USually the "beaten" oil lays on top so it is not so likely to be sucked into the pickup.

Obviously as noted, it can also result from an air leak in the suction side.

[aquacraig@shaw.ca]

As mike suggests, bubbles are most likely aeration, which is the normal event of over or under fluid level. More fluid is not better...an automatic car tranny can fry in a few thousand miles if over filled.

Craig

[Captned]

It happened to me once. The oil level was low...


Captned
MBMM