Engine oil in marine gear! Now I see it....now I don't.

[Chapeaux!]

In June this year, we ran from Stuart to Fernandina on trip to Great Lakes. Before leaving Fernan., (about 05:30) checked all fluids. Port engine (I haven't named it yet) 8V71-TI down 2-3 quarts...port marine gear (Allison unit) overfilled by corresponding amount...and black. Obvious by color that engine lube oil somehow migrating from engine into marine gear. Rather than start to Beaufort, SC outside, we waited and called our engine guy. Confirmed that only way for oil to migrate is through the crankshaft seal, as there is only one seal between eng and gear...but he told us that the rate at which it normally transfers is slow and advised that there was no immediate danger to engine. We could wait and replace seal when we arrived on Gt. Lks. Advised us to stop about half way between Fernan and Beaufort to check both eng oil level and marine gear, just for safety sake. We purchased a hand operated vacuum pump w/reservoir and thin tube and pumped excess oil out of marine gear. We did this, because we anticipated needing to do this on a regular basis as we travelled North. Stopped and checked both oils about half way to Beaufort.....no change. everything cool. Checked again, and again, and again, all the way North and all the way back to Stuart. Haven't yet had another occurrence of problem. My question is this: Has anyone had a similar experience? I suspect that someone has. Could use some input.

By the way...Merry Christmas and Happy New Year.

 

[captddis]

I have seen them go for a year or more then get black oil again. There can be no rhyme or reason. One cust ran the boat 10 more years after the first occourance, changing the gear oil when it got black. I would monitor it and check the levels daily.

 

[Chapeaux!]

Thanks Cap, I had pretty much decided to drop into the "let sleeping dogs lie" mode with this one. We just recently got back to Stuart and are planning to leave for the islands between fronts around mid-Jan. If I wanted to do anything besides monitor this one, I'd need to do it now. Appreciate the confirmation. Guess I'll change oil in the gear again, so it's easier to watch for subtle changes in color.

 

[mike]

FWIW, given the amount of leakage you describe, the problem could possible be caused by excessively high crank case pressure, and or and overfilled crankcase. I would make certain my breathers and air box drains are all working properly. The lower half of the rear seal is real close to the engine oil level in the oil pan. It would not take a tremendous amout of crankcase pressure to force oil into the transmission. This is especially true if you have been running at high RPMS for an extended period of time. I believe the spec is 1.3" (of water) @ 1800, 1.7 @ 2000 & 2.0" @ 2100 RPM. Use a manometer to take the readings at the dipstick opening. "Potential root causes of excessive crankcase pressure are; worn rings, holes in pistons, defective blower, head gaskets, or excessive exhaust back-pressure. Breather tube or crankcase ventilators should be checked for obstructions." My bet is the engines have not been run frequently and that the rings may have gummed up and were sluggesh; or there was some temporary obstruction in the either or both the breathers and exhaust. By the way, replacing the rear seal is a real pain, therfore like already suggested I would monitor the problem to see if it reoccurs. I replaced my seals on our 35 year old 4000 hr 8v71n's, and they were still in reasonably good shape. Good luck, Cheers, Mike

 

[Genesis]

Yeah, I wouldn't screw with it unless it happens again.

At that rate you almost certainly were PUMPING (not leaking) the oil. This points towards high crankcase pressure - I WOULD check that.

 

[Chapeaux!]

FWIWMy bet is the engines have not been run frequently and that the rings may have gummed up and were sluggesh; or there was some temporary obstruction in the either or both the breathers and exhaust. Good luck, Cheers, Mike

Thanks, Mike. You may be right about the gummy rings. We normally put about 150-200 hrs annually on Chapeaux! which means she's not sitting around all of the time. However, from Aug 05 until Mar 06, she was in the yard and ooc due to lightning strike ( http://www.adrift-again.com/zapped.htm ) off Grand Bahama in early '05...electicals, complete paint....engines not run for nearly the entire time . Left for Exumas in late Mar 06, returning to Stuart in May. Oil changes and departure for Gt Lks in mid June' 06. Ran pretty hard up to Fernandina where we discovered the oil in gear. Perhaps the hard run to Fern did the job of burning the sludge from under the rings. However, the engines have never smoked on startup and I normally carry the oil level near the low mark on the dipstick...always have with Detroits. Seems like the first two or three quarts blow out pretty fast anyway if I carry them full. Our normal cruising RPM's are around 1500, but when we need to cover a little more ground, we spool them at around 22-2300. She gets a little soot (what I consider normal for Detroits) after a long run at 80% power. Engines have about 700 hrs on rejug. Always use a little engine heat several hours before startup. I'll take your advice and check crankcase pressure...that's a pretty straight forward one to get done and one I can cover before we plan to leave again..

 

[bobk]

How do you check the crankcase pressure? I may have similar issues.

The seal on the port engine was replaced in 2000 (500 hours ago) when it was majored. When I bought the boat in June, the trans oil was a bit dark. Changed the oil (300 hours on it) and it looked OK for the next 20 hours or so. Just before we started south, we changed engine oil and the mech added 5 gal to the crank case and a couple of quarts to the filter. We began to use/lose some oil and the tranny took some on. Once the engine oil level dropped a couple of quarts, it seemed to stabilize. I've left it like that and monitor daily. Oil pressure is normal even two quarts low.

Bob

 

[Chapeaux!]

How do you check the crankcase pressure? I may have similar issues.

The seal on the port engine was replaced in 2000 (500 hours ago) when it was majored. When I bought the boat in June, the trans oil was a bit dark. Changed the oil (300 hours on it) and it looked OK for the next 20 hours or so. Just before we started south, we changed engine oil and the mech added 5 gal to the crank case and a couple of quarts to the filter. We began to use/lose some oil and the tranny took some on. Once the engine oil level dropped a couple of quarts, it seemed to stabilize. I've left it like that and monitor daily. Oil pressure is normal even two quarts low.

Bob

Bob, Mike's post (above) pretty well explains the process of checking the crankcase pressure as I understand it. Although I've not yet done it myself, I've watched the engine guys do it during surveys, during both purchase and sale. Usually, the way they do it is to connect their various gauges to the engine before the sea trial begins and then record the numbers as the run progresses. I imagine Mike will expand on the process necessary to get it done if you ask. I'm planning to perform this test when I get back from grandson's birth on Ohio in early Jan. As far as your description of your oil levels, I've had both 6-71's and 8-71's and found, as you are finding, that keeping the oil level topped off at the full mark seems to cause the first couple of qts to drop pretty fast and then the level stabilizes. I never let the level drop below the "ADD" mark, meaning that the engine still has about 20qts of oil...plenty to cover normal running losses. A good number of the Detroit drivers I've talked to seem to do something similar.

 

[MikeP]

Runninig the oil level at the add mark rather than the full mark is pretty common on older engines of all sorts to reduce oll consummption. The closer the crank is to the oil level in the pan, the more oil is "misted" by crancase windage. There were studies in the 60s that demonstrated that crank windage could actually cause a several quart "cloud" of oil to envelope the crankshaft. This mist then was easily blown out via whatever crank ventiilation existed. It also reduced the oil available to the engine for lubrication. Windage trays were used on performance engines for this purpose - they "peel" the cloud away from the crank and allow it to drain back into the pan. Any time there is excessive oil mist in the crankcase, it can be blown through seals/etc where oil would not go if operating properly.

NOTE that this existed with the oil at Normal levels - several inches below the bottom of the crank and its throws. The crank should never, under any circumstances actually contact liquid oil in the pan. The farther away from the crank you can keep the oil reservoir, the better.

That's why lowering the oil level will often reduce consumption.