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sourcing 20W hydraulic oil/fluid?

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Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
Printed Date: May-22-2024 at 2:31pm

Topic: sourcing 20W hydraulic oil/fluid?
Posted By: Splitrock
Subject: sourcing 20W hydraulic oil/fluid?
Date Posted: January-17-2023 at 9:42am
Hi, a question for the group - where can one find 20W hydraulic oil/fluid?

Asking because I just acquired a 1988 ski nautique and from what I can tell the transmission fluid is not ATF. The fluid is clear and not red - the smell is neutral. The boat has been extremely well cared for (single owner, stored indoors and and serviced annually with only 350 hours) From what I have read within the email thread (linked below), Eric recommends staying with the 20W as replacing it with more conventional Dextron would require an extensive and complete flush.

Anyone else run into this dilemma? (older boat running 20W in the transmission) 

transmission oil thread" rel="nofollow -

Many Thanks!

Posted By: KENO
Date Posted: January-17-2023 at 6:13pm
Most any place that sells tractors should be able to help out.

Since you have a Borg Warner 10-17 in an 88 SN there are enough different manuals from B/W and also from companies that used that transmission to just totally confuse you on what to use. Recommendations changed numerous times over the years as oils and their specs changed

Mercruiser used the same transmission in lots of Mercruiser powered ski boats and they say an alternate you can use in place of Dexron 3 is Mobil 424. You don't have to decipher a bunch of specs, you just ask for Mobil 424 Wink

Is Mobil 424 a 20 weight oil? beats the hell outta me, but it's recommended by name as an alternate to ATF.

If the boat has been meticulously maintained are there any written records that might tell you what was used?

You can decide what you want to do, but the one oil that comes up universally is Dexron 3 or Dexron/Mercon
(a later version of the Dexron 3)

A flush isn't exactly hard if you decide to go that route

Pump it out with a small hand pump, put in the ATF, run it for a few minutes, putting it in Forward and Reverse, turn it off pump the ATF out.

Do this 3 or 4 times or till you're happy.

If you do this on the trailer, make sure that along with supplying water to the engine, you wet the strut bearing so that bumping into Forward and Reverse doesn't damage the strut bearing.

When was the oil last changed?     If it's clean like you say, I'd run it for this next season

Posted By: Splitrock
Date Posted: January-17-2023 at 9:47pm
Thanks for the details. Extremely helpful!

Appears the search for 20w trans fluid now has some additional complexity. Vendors of 20w oil typically sell the fluid using the equivalent "ISO VG" classifications (see chart below) - so of the two ISO VG grades associated with SAE 20w, which would work best in a Borg Warner 10-17Something closer to 15w (ISO VG 46) or 30w (ISO VG 68)?  Wacko

Conversion between ISO, AGMA, and SAE oil standards for Viscosity Index 95

Posted By: Jonny Quest
Date Posted: January-17-2023 at 10:31pm
The flush is not that difficult.  I recommend giving serious consideration to KENO’s suggestion about going with Dexron III or Dexron/Mercon.  

If you have a fluid extractor, then it’s even easier.


2003 Ski Nautique 206 Limited

2001 Ski Nautique Open Bow
1994 Ski Nautique Open Bow

Aqua skiing, ergo sum

Posted By: KENO
Date Posted: January-18-2023 at 7:31am
I think I'd listen to Jonny's suggestion myself or use Mobil 424

In 1988 your B/W transmission most likely left the factory with ATF in it.

It wasn't Dexron 3 though because Dexron 3 wasn't born yet

That chart doesn't exactly do anything to simplify anything Wink

Posted By: 67 ski nat
Date Posted: January-18-2023 at 8:48am
Yes. I’d go with Keno suggestion of Jonny recommendation to follow keno

Posted By: Splitrock
Date Posted: January-18-2023 at 8:31pm
Thanks for the continued input. Just a note that continued digging shows Dexron ATF to have an ISO rating of 32 (so something closer to 10w) So it appears that as the ATF fluids evolved, the viscosities for velvet drive units got lower? And/or perhaps the gearboxes evolved too. Evidently early velvet drives could run 40w under certain lower RPM conditions. Stern Smile

Another question - does anyone notice gearbox performance change in colder water? Unlike an auto, the older boats transmission fluid is more subject to temperature variation due to heat exchanger design (i.e. use of lake water)

Posted By: Splitrock
Date Posted: January-18-2023 at 8:44pm
From early velvet drive manual -


Dexron@II, Type F, and other hydraulic transmission fluids which meet the Detroit Diesel Allison Type C3 specifications are recommended for use in all Velvet Drive@ marine transmissions.

Lubricating oils which are recommended for use in diesel engines and also meet Detroit Allison Type C3 specifications may be used if the engine speed does not exceed 3000 RPM. SAE #30 is preferred. SAE #40 is acceptable if high operating temperatures are to be encountered. Multiviscosity oils such as 1 OW-40 are not acceptable. The first choice is an oil which falls in the SAE-API service Class “CD.” The second choice would be an oil which falls in the SAE-API service Class “CC.”

Posted By: KENO
Date Posted: January-19-2023 at 6:16am
I guess some continued research would be to look at a newer velvet drive manual and an older velvet drive manual and do a part by part comparison.

Have you researched the Mobil 404?  It's fairly easy to find info on it

Is your next research project gonna involve figuring out what  oil to use in the engine?

BTW  I'd now go with 67 ski nat's suggestion a few posts back Wink

Originally posted by 67 ski nat 67 ski nat wrote:

Yes. I’d go with Keno suggestion of Jonny recommendation to follow keno

Posted By: Riley
Date Posted: January-19-2023 at 10:32am
We've bought boats that appeared to have oil in the transmission and switched them over to Dextron III with no issues. 

Posted By: KENO
Date Posted: January-26-2023 at 9:00am
As I was pouring some ATF into a snowplow  hydraulic reservoir yesterday, this thread popped into my head and made me say  to myself " I wonder what Splitrock decided to do? " Wink

Posted By: Splitrock
Date Posted: March-06-2024 at 9:15pm
To close this thread - below is what I learned and the option I chose.

I learned the following:

a) a Borg Warner 10-17 transmission will run on just about any non synthetic oil 

b) Keno's suggestion to see 67 ski nat's suggestion referencing Keno's suggestion of Jonny recommendation to follow Keno

c) Grand Poobah status has merit

Option I chose:

Flushed the transmission several times (following best practice for inboards out of the water) making use of Dexron/Mercon. I used a 12v gear lube extractor which made this task easier/faster. 

Results are great! Now looking for a new prop Wink

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