Synthetic auto trans fluid

Sorry for typos.
...typing from my phone.

psneeld said:

Pulled my tranny this week for a dampner plate replacement.

Sending the tranny out for seals and a look inside.

I will let you know what the repair facility says about using 30Wt.

I have no doubts after beating up a fleet of trannys filled with 30wt that get a marine beating like Baja dune buggies beat their systems.

I usually only take a stand about this stuff when I have a lot of practical, real life experience with it.

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Forgot to update.....tranny in perfect condition running decades on 30Wt oil.

Thermal conductivity for SAE30 is about .12W/mºC; for ATF about .13. so about the same.

Viscosity for SAE30 at 30 deg C is 147, for ATF is 52.
At 80 C SAE30 is 18 mm sq/sec, for ATF is 12.

If the design calls for a viscosity of mid teens, then you can see the thickening of the SAE30 cold will not be welcome. It would cause more drag in the fluid pump. Operation at a freezing start up would be more dramatic.

And not one sign of wear and tear on my boat or a fleet of assistance towboats that beat trannys to the ground compared to recreational trawlers.

And that includes winter operations in freezing temperatures in NJ winters.

It warms up quick enough.

jleonard said:

The upgrade is that motor oil is a better lubricant for bearings than tranny fluid.

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Got a reference for that?
"motor" oil has additives that make it last in motors.

psneeld said:

And not one sign of wear and tear on my boat or a fleet of assistance towboats that beat trannys to the ground compared to recreational trawlers.

And that includes winter operations in freezing temperatures in NJ winters.

It warms up quick enough.

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I doubt you not. My point is simple, SAE 30 has a 100:1 viscosity change from 0 to 90 C. ATF is much less. I don't see now a compelling reason to not use ATF when specified. Plus, its red and shows leaks.

Many will debate that oil is a much better lubricant than tranny fluid. Tranny fluid for complex shifting is one thing, heavy weight oil for simple gear cases is another. One might argue that a simole BW tranny doesnt need the characteristics of tranny fluid, just oil.

Thats why our lead mech ran oil in the towboat trannys because of the hard service life.

My manual says run either tranny fluid or oil.

After seeing about 100,000 hours on a fleet of boats and none having tranny leaks anyway, red fluid color isnt a big deal for me. Iwould rather run oil and not have leaks.

But follow the crowd, they have had good luck too.

diver dave said:

Got a reference for that?
"motor" oil has additives that make it last in motors.

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No. Just my years of working with engineers that designed and tested bearings in many different applications. They did not like having to be in an ATF application because bearing life was usually lower.
That's one issue that I used to base MY decision on, then had a lubricant discussion with the guys at Atlantis Gear that had 30 experience with Velvet Drive trannys.
Because of a very crappy environment and a tough application for a bearing I made my decision and I'm not looking back.

Frankly, the lube rqmts of a boat transmission appear to pale in comparison to its engine. Think about the various, sometimes opposed, lube issues on a motor. High speed shell bearings with dynamic loading that rely on oil pressure, low speed cam to follower rubs, piston ring scrapings, piston pins without oil pressure, etc. And the designer only gets to pick one lube to deal with it all. In the end, it is manytimes the worst case bearing gets to make the call on viscosity, etc. BMW M3 engines are specing a 60 weight oil due to a rod bearing demand. Weakest element in the chain.

Meanwhile our boat trannies have clean working conditions, no blowby, no acids forming, no shell bearings, no cams, no ring scrapings, no combustion heating the assembly, etc. Basically, keep some ball bearings alive and keep the gear rattle down. You can keep the forward, reverse pistons in place with just water, if you needed to. The oil pump is predominately only feeding the spool valve to squish the wet clutch plates together and circulate to a remote oil cooler. Splash wetting of the bearings. Not a tough job.

I was able to kill a VD, but it took seawater to do so. I would have no issue running ATF or 20 or 30 motor oil. It just doesn't matter. btw, Dexron is hydraulic OIL with a fair amount of antiwear additives running about a 5w-20 viscosity. About the same amount of detergents as motor oil.

Fine with me. We all have opinions.