Yanmar 3GM30F Rebuilt transmission is leaking

[FuneSF]

I recently had the Kanzaki KM3P transmission rebuilt on my Yanmar 3GM30F.

I put about 5-6 hours on the engine since the rebuild. The transmission and engine ran beautifully. But, I now notice the transmission is leaking fluid. I have not located the exact spot, yet.

My question is: The mechanic at the boatyard put Havoline ATF MD-3 into the transmission. The manual and the tag on the engine specifically specifies the same oil as the engine. I asked the mechanic why he was using ATF fluid. He said that the shop, where the transmission was rebuilt, is recommending the AFT fluid. He said ATF has changed considerably since the engine manual was written in the 90s and it is fine to use ATF now.

Anyway, the fluid is leaking. Do you think the ATF fluid could have ruined the seals? Do you think the thinness of the ATF fluid compared to 30 weight motor oil is exacerbating the leak?

I know I'll need to get transmission seals redone. But, I wonder if I switching back to the recommended motor oil will buy me some time (I'm departing on a three week trip in September).

[tkeithlu]

When hot, the viscosities are about the same. No, I don't think ATF damaged the seal(s), since no shop would have used a seal that would, particularly if they recommend ATF. It sounds more like someone goofed - there's a bad seal in there.

So, the question becomes warranty on the transmission rebuild, size of the leak, and time until you leave.

[FuneSF]

Thank you

[Lepke]

Check where the seal rubs. Sometimes there will be small pits that eat a new seal. There is a sleeve available that slides over the shaft and give a new surface.

[FuneSF]

Thanks. I spoke with the boatyard and the place that they had rebuild the transmission. The boatyard incorrectly put the ATF fluid into the transmission according to the transmission shop. According to the transmission shop, there were only a few hours on the transmission using the ATF fluid, so, there is likely no damage.

I replaced the ATF fluid with the correct motor oil. I ran the motor fairly hard for about four hours at about 3000 rpm around the Puget Sound. There was no leakage and the transmission ran without any issues. I'm going to flush out and add new motor oil next week to make sure the ATF fluid is gone.

If the leak reappears or any transmission problems develop, the boatyard said they would repair any work needed under their warranty.

[Wotname]

That sounds like a good outcome, thanks for the update.