ATF or SAE ? Yanmar 4JH2E / Trans: KM4A - SailNet Community
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post #1 of 5 Old 11-05-2007 Thread Starter
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ATF or SAE ? Yanmar 4JH2E / Trans: KM4A

Last week I was checking the transmission fluid on my Yanmar 4JH2E / Transmission: KM4A. The boat; a 94' Caliber 40 is new too me as of one year ago. The ATF was a little low but as I am about to change the Oil for the last time this year for winterization I made a note to change that too in the coming week.

As I was putting the cap back on I studied the plate on the front of the transmission, I then relized it actually calls for SAE 30 wt. Apparently the Previous Owner was using ATF and it was missed be me (and my surveyor..) I have since confirmed on a couple of Yanmar sites that it calls for the same oil as the engine.

Now I am not sure what to do. Keep using ATF or switch to Oil? I had the discussion with a fellow Yanmar owner and he was of the opinion that I should keep using ATF under the stratagy of not messing with something that seems to work. I am not sure thats good idea.

The Transmission runs fine - altho occasionly it seems to take a second or two to slip into gear. Not sure if that would have anything to do with the oil..

Any thoughts?

s/v Mahalo
Caliber #4065

ACM - Eastport MD
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post #2 of 5 Old 11-05-2007
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ATF - Automatic Transmission Fluid - used in automatic transmissions on cars and in "hydraulic" gearboxes on boats. A manual/mechanical shift box might well be happier with SAE 30 engine lubricant. But anyway, guarantee terms demand that the recommended product be used. I would drain it and used the YANMAR recommended product.
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post #3 of 5 Old 11-05-2007
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Yanmar have used both ATF and SAE30/eng oil in their gearboxes. General rule: disk-clutch=ATF, cone-clutch SAE30/engine oil.
Main reason is the breaking of the oil-film by the clutch-system to obtain the friction/engagement of the clutches. The film-thickness in the SAE30 is more difficult to breake for the plate-clutch, the cone clutch engages with much more force and less friction surface and should manage if all is in order.
The following link might be a help:

There is no big problem to change the oil, but You should do at least 2 changes to wash out the old oil. The reason for the old owner to have ATF might be the symptom You describe as 'delayed shifting'. This might encrease with the use of SAE 30 oil. Whatever You do, do not go syntethic.
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post #4 of 5 Old 11-05-2007
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Funny you should ask because I have the same situation with my 1988 vintage Yanmar 2GM20F and the Kanzaki tranny (sorry, but I don't recall the model number off the top of my head.) I have changed the ATF several times (I've owned the boat, a Pearson 33-2, for 4 years) and this past spring noticed what was on the plate on the back of the tranny. I have consulted various Yanmar experts, including Mack Boring at the boat show and a fellow named Chris Oliver in Annapolis, well known as a Yanmar guru. Neither one was all that alarmed over it because apparently the lube capabilities of the ATF are well within the range the Kanzaki requires. But both said to drain it and replace with SAE 30 wt oil as the manufacturer intended. But as with you, I am reluctant to change something that has been working all these years. Yes, I did consult the prior owner, who owned the boat for most of her 14 years before I bought her, as well as the mechanic who serviced the engine many of those years for him. The mechanic said it had always had ATF in it so he simply replaced it as needed. He never thought anything about it.

Despite history, however, I probably will drain and replace with oil this fall -- several times in fact to make sure I get all the ATF out.

BTW, you're the second Caliber owner I have encountered with this same situation.

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post #5 of 5 Old 11-05-2007
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My Yanmar 2gm16 also specs 30wt in the trans. it appears to always have had 30wt, being as PO was OO too!

I wonder if Caliber felt it better to have ATF in the trans vs 30wt, and as such, when they installed the motor/trans, they put in ATF. A thought, nothing more!


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I drives me dinghy!
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