Re: Older style C-Drive; oil type and temperature

Dan Carlson

On SM #387, with a newer design c-Drive and larger 100hp Yanmar, I have also recorded similar temperatures.  If I'm motor-sailing at 1600-1800 rpm the temp at the top of the c-Drive may be 60C, at 2000rpm it's closer to 70C and 2200-2400rpm It gets closer to 80C. 

Last season was my third year on the same shaft seals. If I ran longer an hour at 2000rpm or more then I would start to see some milky oil coming up the return line into the top of the reservoir. This would settle out between runs and would not come up if I was running less that 2000 rpms, no matter how long. This leads me to believe that the circulation of the oil (at least any water in the oil) may be somewhat driven by temperature. 

I had lots of extra oil 80/90 oil as I had purchased a 5 gallon container from NAPA auto parts in anticipation of my next oil change (cost less than $80 US). So when I saw "cream" in the reservoir, while it was still hot, I would drain the reservoir, refill with clean oil, then I used a 6.5 liter fluid extractor (suction) on the return hose (top), to suck a couple more liters off of the top of the c-Drive gear box. This got me thru the end of the season when I did a proper oil and seal change. At that time I found that the retaining spring on the outermost oil seal had broken and that is the seal that is supposed to keep the water out. The inner two seals were still in good shape so water ingress was minimal. 

Best regards Daniel and Lori Carlson on sv BeBe, SM #387 

On Thu, Dec 30, 2021, 4:48 PM Mike Longcor (SV Trilogy) <svtrilogy53@...> wrote:
Hi Bill,

On SM hull #23, the part of the C drive that is in the water (aft end of the keel), is GRP. It does have differences from newer drives like the oil drain bolt is on the port side rather than below the prop shaft. The upper gearbox that is visible in the engine room is aluminium. On the newer models, the upper gearbox visible in the engine room is larger and made of iron. I've attached photos of each one. Rusty one is iron, naturally.

I took temperature measurements and must conclude that heat is generated by the C-Drive itself. The Hurth gearbox, drive shaft, Vetus coupling, and all parts connecting the top of the C-Drive to the engine are cooler than the engine and the C-Drive.

Below 2000rpm, the C-Drive measured around 70C at its hottest spot. At higher revs, I measured just under 80C. Between the engine and C-Drive, I was getting measurements from 40C to 60C. As Amel said, there are a lot of parameters to take into account when taking temperature measurements of the C-Drive. There are also variabilities and inaccuracies with using a temp gun, but it gives a ballpark idea.

To summarize the oil recommendations as I understand them:
Smaller aluminium gearbox C-Drive gets 15W-40.
Larger cast iron gearbox C-Drive gets 80-90.

I've never seen or heard about an all aluminium C-Drive until now. Very interesting.

I hope this serves to eliminate confusion rather than create it.

Mike Longcor
SV Trilogy SM23

On Mon, Dec 27, 2021, 1:30 PM CW Bill Rouse <brouse@...> wrote:

In order to be completely clear to everyone in the group, I believe that you are referring to the Aluminum case C-Drive which was short-lived and replaced by the GRP case C-Drive. And, to be clear, there have been at least two versions of the GRP case. I am sure that there are other modifications like the increased shaft size beginning with hull 43 on A55s.

I have been aboard many SMs, 54s, & 55s. The GRP C-Drive will normally get to the operating temperature of the main engine, or about 80C. I believe this temperature exists because of some heat transfer from the main engine, rather than any internal heat generated. I assume that some heat is transferred to seawater because the C-Drive is in contact with seawater. This transfer would be greater with aluminum than with GRP.


CW Bill Rouse Amel Owners Yacht School
720 Winnie, Galveston Island, Texas 77550 
On Sun, Dec 26, 2021 at 1:53 PM Mike Longcor (SV Trilogy) <svtrilogy53@...> wrote:
Hello Everyone,

Just following up on this thread with some information sent to me from Amel. This is in regards to the older style C-Drive, in case it's relevant for anyone else out there:

"The recommended oil for the C-drive is 15W40 and you need 8 liters. It is not recommended to use a thicker oil on this system. It is true that there are some confusing discussions about this issue especially on the different social networks.

We have no exact operating temperature value of the C-drive  but it should be between 60 and 70 °C. There are many parameters to be taken into account when doing a temperature test (for instance the outside T° can influence the result).

AMEL has never launched any retrofit campaign regarding the replacement of your system with iron units. This operation is mainly considered when the aluminum C-drive fails and breaks and that there is no other alternative. The cost of the new system (including Upper and lower C-drive unit) is around 20 000 euros without labor and requires high skilled mechanical engineers to do the work. If the maintenance on your C-drive is correctly performed and if there no sign of dysfunction there is no reason to proceed with a replacement.

At last, it is indeed  better to repower your boat with an engine rated 78hp or close to it to avoid any excessive mechanical stress on the C-drive."

Mike Longcor
SV Trilogy SM23

On Wed, Nov 3, 2021, 7:55 AM Mike Longcor (SV Trilogy) via <> wrote:
Hello everyone,

I'm curious if anyone out there still has the old aluminium C-Drive installed in their SuperMaramu?

Is the 80-90 gear oil recommended for both C-Drives (aluminium and cast iron)?

What is the operating temperature range for the C-Drive (how hot should the upper gearbox get while motoring)?

I'm also asking Amel these questions and will respond here with any useful answers I get back. I have a feeling there aren't many aluminium C-Drives still out there...

Mike Longcor
SV Trilogy - SM23

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