Synthetic Oil in Tranny Experiment Results

[spartonboat1]

Ok, since I am a synthetic oil geek, I had to try some in my trannies, Twin-Disc MG-506's last summer. I ran the same 40wgt Mobil 1 Delvac 1, which is specifically for Diesels and which I run in my 7.5Kw Onan genny with good success (no oil consumption observed during the 6 month season).

However, the synthetic oil in the trannies didn't seem to work out. I found that both trannies seemed to "use" oil and I had to add oil to both, esp. to the stbd. I was actually below the add mark at one point and the tranny sounded grumpy.

So this year I switched back to Texaco Ursa 40, same as is in the mains, and with about 10-12 hours runtime I am observing no reduction in oil levels in either tranny. So you can say that my experiment is probably complete. I will watch the oil levels the rest of the season and report back at the end.

I always find it interesting that the oil in the trannies is/remains so clear that it is barely visible on the dipstick. Also, for some reason I never seem to achieve 300#'s pressure, but closer to 270-290#'s. However, this has been the observed pressure at cruise since I bought the boat in 1997 and is consistent, so I view it as "normal" in my 1972 vintage units.

[krush]

There is no combustion and not huge amounts of heats in trannies...so the oil stays clean! Manual car transmissions are the same way. That's weird that the oil is disappearing....the only place for it to go is into the bilge, out a cooler leak, or into thin AIR!

How many hours were on your generator when you switched over? Did you have any problems with oil leaks?

I've had some friends put synthetic oil in older higher milage cars (150k +) and they ran into problems with seals leaking. My "theory" is that the synthetic acts as a cleaner and cleans out all the "gunk" from the worn seals that is holding in the oil. Once the gunk is gone, the seals begin to leak.

Of course, if using synthetic from the beginning of the engine's life, the seals would never wear like with dyno oil...at least that's the assumption (I believe it though, the stuff is amazing). Sadly, everything I acquire is already worn out when I buy it, so I don't have to spend the extra money on synthetic oil haha.

[TedZ]

If you have a 7.5 KW Onan that doesn't use/leak oil it belongs in the Smithsonian!! :--)

Ted

[jim rosenthal]

Couldn't the transmission oil leak past the front seal and into the engine, if it could get past the rear mail seal? Or is there no direct path?

[spartonboat1]

Just why the trannies seemed to "use" the synthetic oil last summer, I cannot say. I will keep a close eye on them all summer to ensure their oil levels don't drop. So far, so good. I just don't want to draw a wrong conclusion.

Regarding the Onan genset (MDJE 7.5Kw), she was rebuilt by the PO by the best Onan man in Chicago. He says he tried to retire, but Onan owners found out where he lived and wouldn't let him alone, so he went back to work. It's nice to be wanted. He told me that my Onan was bench re-built.

At any rate, I watch the genny lube oil level and basically it does not move on the stick during about 25 hours runtime during the season. This is running the Mobil Devac 1 40wgt specifically for diesels. I do try to run at the 70% of load factor, although sometimes need to idle it; try to avoid idling though. I did need to replace the glow plugs and the hot plate (pre-heater), which had gone bad on one side.

Lotsa ticky-tacky issues, which now are all resolved and she starts first time about 99% of time. She does smoke on one cyl for about a minute or two, and I run a 50-60% load to heat her up. Then she runs clear exhaust all the time after that.

Seems like most of the issues with this boat over the past 10 years have been resolved by bringing her back to the original, solidly installed configuration as new, i.e. overcome the sloppy, poor approach to maintenance in the past. No household wiring, no wire nuts, use heavy duty ABYC approved parts and supplies. The whole boat runs better than ever these days.

[Maynard Rupp]

Couldn't the transmission oil leak past the front seal and into the engine, if it could get past the rear mail seal? Or is there no direct path?

Jim, the bell housing is between the tranny and the engine and is a dry area that contains the flywheel and starter ring. If either the tranny front seal leaks or the engine's rear seal goes poof, the oil will drain from an opening in the bottom of the bell housing and into the bilge.

[SKYCHENEY]

Jim, the bell housing is between the tranny and the engine and is a dry area that contains the flywheel and starter ring. If either the tranny front seal leaks or the engine's rear seal goes poof, the oil will drain from an opening in the bottom of the bell housing and into the bilge.

Not true with an Allison gear, Maynard. The Allisons have wet flywheels.