The Venerable RC8D

[DaBod]

Hello all,

I've been lurking and using this site for information for quite some time and think it is time to start participating.

My 1980 H27 has its original Renault RC8D and it is going strong. I bought the boat just under a year ago and have been trying to nurse her back to health. She seems solid as a tank and really all I have had to do is replace old fuel and change the oil several times. Those simple tasks resolved the bulk of its smoking issues, but she leaks. It seems to be coming from the transmission and is getting worse, so at some point in the future I am planning to replace the seals. It seems that crawling back there to disconnect the transmission might be the toughest part of that job...not really looking forward to it.

I haven't yet been able to pinpoint the leak, but haven't poked around too much when the shaft is spinning. I watched the floor of the engine compartment for 5 or so minutes and didn't see any drip, but 30 minutes after engine shut down there was a nice sized pool of oil in the compartment.

Could it be something other than a seal?

What do you use as transmission fluid? And how much? The previous owner used SAE 10w-40 in both the engine and transmission. I've switched to Shell Rotella in the engine, but have continued using 10w-40 in the transmission. Thoughts?

Thanks in advance!

 

[JoeWhite]

To the best of my knowledge - engine oil is not used in the transmission. The correct oil for the transmission is Dextron II or III - which is the same oil used in auto automatic transmission. This is what is specified for my transmission. It is best to check with the manufacturer to be sure.

 

[DaBod]

Thanks for the response. It seemed strange to me to use SAE oil in the transmission. Fortunately it doesn't seem to have done any harm over the years. I'll keep researching, but will plan on switching to a more appropriate fluid. That'll probably pretty easy to do since the reservoir will likely have leaked itself dry by the time I make it back out there.

 

[DaBod]

I just heard back from a shop in the UK that is apparently the only remaining supplier of parts for the RC8D.

According to them, a quart of conventional 20/40 engine oil is the correct fluid for the RC8D transmission. Seems strange to me, but it has kept the shaft turning since 1980, so I guess I will stick with it!

 

[rardiH36]

Don't feel alone about your transmission requiring motor oil. Whereas the late 1970's transmission mated to my Yanmar 2QM20 calls for ATF-A (several generations ago standard automatic transmission fluid), 10W-30 motor oil was specified by Yanmar for the KM2-C, KM3-A, and KM3-V transmissions that were mated to their GM series engines.

The previous owner of my boat had on board the Yanmar manual for the GM series ... not the QM series. As a consequence, he filled the ATF-A transmission with motor oil for 20 years! Seems not to have done any harm. Actually our local authorized Yanmar service parts shop said motor oil wouldn't be the first choice, but it is a workable substitute. (However, they advised to change to the ATF.)

 

[redhead78]

I am the previous owner of a RC-30D, in my jeanneau 38, as part owner, I kept that engine going for 15 yrs, once running it was not too bad, leaked everywhere, parts were unavilable. Every time I started it was a new problem, dual impellers burned up, I installed a small 12 volt flojet pump just before the empty impeller chamber, worked great for couple years,had to be very careful about hydrolocks,the head gasket proved to be terminal, the end....can,t say bad it pushed that boat around the world for 30 yrs....good luck Red

 

[Benny17441]

That is correct more marine transmissions use regular motor oil than automatic transmission fluid. Our dealer filled our tran with ATF and it seemed like everytime we went out we had to top off the fluid. We then checked the yanmar manual and the correct fluid was 30 weight motor oil. We filled it up and now only check the level every six months and hardly ever have to add any. Since the transmission is a clean sealed enclosure the oil will last for a long time and if you use a premium synthetic you may not have to change it during your ownership of the boat.

 

[DaBod]

And the plot thickens...

Just got my hands on an owner's manual and discovered the way that the previous owner told me to check/fill the transmission oil is very incorrect. This leaves me to guess that he and I both have been grossly over-filling the transmission for a very long time.

My fingers are crossed that the "leak" I am seeing is actually the overfill being spat back out through a vent or something, although with my luck I'd guess that overfilling has blown the seals. :cussing:

 

[txmilke]

Venerable, indeed

Yes, the manual recommends SAE 30 motor oil. I also have this engine and it has never failed me. I also have some leaking from parts unknown which only started recently. Would be interested to find out what the source of yours is.
There is a user's forum on Yahoo regarding these motors. Check it out. When needed, I have purchased parts from a guy named Tony in Ireland without difficulty.
Tom

 

[DaBod]

Yes, the manual recommends SAE 30 motor oil. I also have this engine and it has never failed me. I also have some leaking from parts unknown which only started recently. Would be interested to find out what the source of yours is.
There is a user's forum on Yahoo regarding these motors. Check it out. When needed, I have purchased parts from a guy named Tony in Ireland without difficulty.
Tom

I'll let you know what I find as I dig into it. I am probably going to go ahead and replace the seals just to be on the safe side. I'm not at all looking forward to crawling back there, but it's a great opportunity to learn.

I've been in contact with Tony and he has been tremendously helpful...sent me manuals and additional info. It's great to know that there are resources for information and parts out there!

 

[Lusitano]

This is what the the Manual recommends SAE 10W30!