# Dexron ATF in my Yanmar Trans Gear?



## jason3317 (Dec 20, 2007)

I tried something different this year and went for the cheaper storage rates in exchange for allowing the yard to do some of the haulout work. 

Imagine my surprise when I saw on my bill "1 QT DEXRON ATF".

I deferred my freak out until I confirmed this wkd that indeed there was ATF in the gear (Kanzaki 2.62 attached to my Yanmar 2GM20F). FWIW, the service manual does specify SAE 30 or equivalent motor oil for the gear.

So, I, with restraint, politely inquired with the yard manager today over the phone about the use of ATF in the gear. He replied that they "checked with Yanmar and they indicated Dexron ATF was appropriate".

Should I save myself a call to Mack Boring to confirm? Who can tell me the correct lube for this tranny?

Jason


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## brak (Jan 5, 2007)

What transmission do you have? My Yanmar can have 4 different transmissions according to manual. The one specifically installed on my boat takes what manual calls "ATF-A". Since no such beast seems to be available anywhere and noone knows what "ATF-A" stands for, it is filled with regular ATF fluid (there are a few out there, I selected the one for the oldest possible American make  ). One of the 4 possible transmissions takes oil. So - it could be either.

BTW, mechanic that I had over on my boat once specified a wrong amount of ATF fluid for my transmissions, which (as I checked later) matched another transmission from the list. Good thing I double-checked and filled according to the manual - or else there would be less than 1/4 of the required fluid there. So, these mechanic guys definitely could be wrong - trust your manual but read it carefully too.


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## bubb2 (Nov 9, 2002)

the owners manual for my Yanmar 2GM20F says SAE 30 weight.


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## jason3317 (Dec 20, 2007)

I think it is a KM2P. It is the shaft drive with 2.62:1 reduction gear.


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## bubb2 (Nov 9, 2002)

I have a 1999 model


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## jason3317 (Dec 20, 2007)

bubb2 said:


> the owners manual for my Yanmar 2GM20F says SAE 30 weight.


Yes, I see the same spec in my SM. But, I am wondering if there was an updated spec issued since my SM was printed (1988)?


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## bubb2 (Nov 9, 2002)

If it has been good on 30 weight for 20 years, don't screw with it now. IMHO


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## LittleWingCA (Jul 17, 2008)

My 1980 Yanmar 2QM15 takes the DEXRON ATF. There is a fill line marked on the dipstick that the fluid level has to be filled to with the dipstick unscrewed and just sitting on the access point.


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## CaptainForce (Jan 1, 2006)

I have 4,400 hrs. on my year 2000 4JH Yanmar with the Kanzakee transmission. For the first 3,500 hrs. I ran it with the ATF Dextron II as filled first by the Yanmar dealer that installed the engine. I damaged my transmission at about 3,500 hrs. due to a faulty control cable setting and the mechanics that rebuilt it filled it with the "proper" 30 weight oil. I've remained using the 30 weight oil, but my anecdotal evidence implies that it functions well with either fluid. Aythya crew


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## timebandit (Sep 18, 2002)

Here you go.

Automatic Transmission Fluid and How It Works


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## timebandit (Sep 18, 2002)

A site for ya'all

TRANSMISSION TYPES


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## jason3317 (Dec 20, 2007)

Seems like the general consensus here is that the yard should have used motor oil and NOT ATF.


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## TSOJOURNER (Dec 16, 1999)

This is an interesting discussion. I don't have a Yanmar. My Volvo tranny drinks the 15W-40 stuff, same as the engine, nice and convenient that way. Never heard of ATF on a boat, but it makes sense in a lot of ways. Many newer gear boxes, transfer cases & such use ATF. It is better for fuel economy, and probably better at resisting emulsification than heavier oils.

I think ATF is chemically similar enough to motor oil where it won't damage the seals, might actually help a little. However I agree that it would be prudent to have them put in the correct oil based on the published tranny specifications.


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## r.furborough (May 28, 2006)

ATF is also recommended in some mechanical transmissions as it also has defoaming agents in it. I have know certain mecahnical transmission dump their oil through foaming, AFT was used and the problem went away.


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## NOLAsailing (Sep 10, 2006)

I can't believe that I've just read a thread where a consensus seems to be forming that you can substitute SAE 30 motor oil for automatic transmission fluid.

I'm speechless.

There's a lot of bad advice circulating on this site.

By the way -- You all do know that there's a difference between gasoline motor oil and motor oil formulated for diesel engines, right?


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## NOLAsailing (Sep 10, 2006)

*IF YOU DO NOT KNOW THE ANSWER TO A QUESTION, DON'T ANSWER THE QUESTION!*


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## brak (Jan 5, 2007)

I think the answer here is that the person needs to know a specific transmission model (which cannot be established based on engine model, since same engine can be fitted with different transmissions). So, we just don't know.


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## NOLAsailing (Sep 10, 2006)

brak said:


> I think the answer here is that the person needs to know a specific transmission model (which cannot be established based on engine model, since same engine can be fitted with different transmissions). So, we just don't know.


Perhaps you're right. I wanted to terminate what I thought was a developing acceptance of substituting ATF and motor oil before someone ruined their transmission. That's completely unacceptable. Maybe I'm just getting a little fed up with some of the answers I've read here over the last couple of months. Maybe it's the weather...


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## AmicaJim (Nov 18, 2007)

Hi all. I read this site a lot and love the information. To NOLA, I worked on cars in the 70's -80's and there were some manufacturers (I specifically remember Chrysler) that put ATF in their manual transmissions at the factory and allowed standard 10W30 to be used after the transmission had worn. 

Yes - there are some applications that allow ATF or motor oil to be used. I don't know if this applies to marine transmissions, but it could! Check your facts before you berate others. 

P.S. Yes, there is a difference in motor oil for gas and diesel engines.


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## TSOJOURNER (Dec 16, 1999)

AmicaJim said:


> Yes - there are some applications that allow ATF or motor oil to be used. I don't know if this applies to marine transmissions, but it could!


 Rumor on the street is that Marvel Mystery Oil is basically just ATF with a couple tweaks here and there in the additive package. Think that is true? I haven't tried that in any manual transmission yet, and don't think I will, but I can attest it sure works magic in gas engines. Frees up stick lifters, stops leaking seals. It mixes quite well with oil. My truck was running really low oil pressure (stuck relief valve I think) after a quart of MMO and a couple trips around the block the oil pressure was back to normal and no more tap-tap-tap in the morning. A4 owners also swear by the stuff. Little off topic but just thought I would pop something into this thread before it turns to a poo tossing contest


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## AmicaJim (Nov 18, 2007)

Sailboy, I have added a qt. of ATF to my oil a week prior to changing it and it does clean things up. got 260K+ miles on it and will be rebuilding this month (just a leaky rear main seal).


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## NOLAsailing (Sep 10, 2006)

> Yes - there are some applications that allow ATF or motor oil to be used.* I don't know if this applies to marine transmissions, but it could!* Check your facts before you berate others.


It could or it does? I need to check my facts?

This is precisely the type of answer that gets to me. When it comes to technical questions, supposition can cause a lot of harm.


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## AmicaJim (Nov 18, 2007)

NOLAsailing said:


> I can't believe that I've just read a thread where a consensus seems to be forming that you can substitute SAE 30 motor oil for automatic transmission fluid.


Sounds like a statement that you can't substitute ATF for oil to me. One contradiction makes the statement false. You didn't specify only marine transmissions. My suggestion for all is to RTFM (read the fine manual ).

Just my .02


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## NOLAsailing (Sep 10, 2006)

The "fine" manual will specify ATF *or* motor oil.

As this is a sailing forum, I'll go ahead and take the liberty now of specifying marine transmissions, in case anyone is a little confused.

So - for marine transmissions, unless you are absolutely certain that you can do so or do do not care about your transmission - you cannot substitue motor oil for ATF or vice verse. Regardless of what anecdotal evidence you find carelessly sprinkled about the internets.

I hope that helps.


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## c40eb (Sep 12, 2002)

Hmmm...I have a Westerbeke 20B Two with JS tranny. The engine manual states it should have SAE 30 oil. When we bought the boat and I first checked the transmission fluid level, it was...pink. Hmmmm...

Well, it's been changed and I am using SAE 30.


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## Faster (Sep 13, 2005)

FWIW, Hurth transmissions DO specify ATF.


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## JohnRPollard (Mar 26, 2007)

Jason,

I have both the Yanmar Operation Manual and the Service Manual for your engine right here. They clearly state that the transmission coupled with the 2GM20F should use the same weight Motor Oil as the engine. Not until you bump up several sizes to the 3HM35F do these manuals call for ATF.

HOWEVER, if you want to know without a doubt, Kanzaki stamps the required fluid into the backside of the transmission housing, just above the output shaft.

In my case, with a 3GM30F and a KM3P transmission, the service manual states to use whichever weight motor oil is being used in the engine. But the stamp on the transmission housing indicates 20W/30. I suspect you will find the same info on your KM2P.


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## jason3317 (Dec 20, 2007)

John, thanks for bringing this back on topic. I will have to check the plate on the trans, just for S&Gs.

Let me add a few clarifying points for the group.

1. I do have and have read both the Yanmar owner's manual and service manuals for my 2GM20F / KM2P combo. Engine and manuals are circa 1988. Each specifies SAE 30 or similar multigrade motor oil to be used in both engine and the gear.

2. I do believe that there is a real difference between SAE 30 motor oil and ATF.

3. I would have used motor oil in the trans if in fact I had done the replacement myself. ATF wasn't even on the radar.

4. I clearly specified on my haulout order the brand / weights of lube to be used in the engine and gear - in fact, I even provided the oil and filter. However, the yard disregarded my instructions and justified by stating they called Yanmar on my specific situation and YANMAR specified ATF. My guess is they didn't correctly identify the gear model if/when they called Yanmar last week.

Now...we all know that the probability of a Yard Error is pretty high. *Bottom line....I think the yard owes me a drain + flush + refill of the tranny.*

That said, I was curious if it is possible that Yanmar has revised their specs to allow ATF in the KM2P gear?


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## sailingdog (Mar 19, 2006)

Jason-

Given they screwed it up the first time, do you really want them to do the work a second time... I'd rather have them pay someone else to do the drain, flush, and refill... 



jason3317 said:


> John, thanks for bringing this back on topic. I will have to check the plate on the trans, just for S&Gs.
> 
> Let me add a few clarifying points for the group.
> 
> ...


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## jason3317 (Dec 20, 2007)

sailingdog said:


> Jason-
> 
> Given they screwed it up the first time, do you really want them to do the work a second time... I'd rather have them pay someone else to do the drain, flush, and refill...


No, I'd rather them redo their work correctly and to my satisfaction, even if they do 10x. It's just an oil change and I don't believe this mistake was intentional, just unprofessional and shortsighted on their part.

As I like to say: "Trust, but Verify".

JS


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