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sea star hyd. fluid alternative. ie: Dextron 3

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oldschoolnc

Contributing Member
Some say yeah. some say no... What do you guys think about using dextron3 in a sea star system. I can re-seal it easy enough if that's an issue.
That $24 a quart is a lot if I can use something else. System is 8 years old, probably need a seal job soon. Would just like to make it until November. It's on a chris craft 215 with a 99 225. Not on my 100+ Hydrostream.....:cool:
 
Dexron II is no longer available.

SeaStar hydrualic fluid is MIL spec 5606 and is NOT the same as ATF. 5606 hydraulic fluid has about 1/2 the viscosity of ATF. In warm weather you might be okay if you use ATF but in colder temperatures you'll have very stiff steering. Also, the detergent packages in ATF are very different from 5606 and may effect your seals.

You can get AeroShell Fluid 41 on Amazon for $42/gallon. It is the same MIL 5606 spec fluid as SeaStar, but is packaged as a hydraulic fluid for airplanes. Same stuff, just half the cost and a 1 gallon container should pretty much last you the life of your boat. I used AeroShell 41 in my SeaStar hydraulic steering system and it's working perfectly.
 
That is a good product, yes. I am also checking with Al, a top Amsoil tech......I know for years, he will let me know if they offer a better alternative. Their full synthetic power steering fluid is 8 bucks per 16 oz. You can look up the technical specs on the Amsoil site. The 4 ball wear test @ 40kg and 75 centigrade 1200 rpm for 1 hour is .46, pretty decent numbers. Viscosity index is 197.
 
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Amsoil has no qualifying product yet, they are working on it, however. The tech there said to go with what is recommended by the manufacturer. The performance requirements are strict. If you think 24 bucks is bad, go price out some parts.......I had to agree with him.......then add 50 to 60 bucks an hour for someone to repair it.
 
timguy said:
Amsoil....full synthetic power steering fluid.....The 4 ball wear test @ 40kg and 75 centigrade 1200 rpm for 1 hour is .46, pretty decent numbers. Viscosity index is 197.
Click to expand...
The main thing I've seen on the MIL5606 specs is kinematic viscosity (cSt). At 100*C ATF has a viscosity of 7 cSt and MIL 5606 about 5 cSt. Not a big deal, but who on earth runs their outboard in 212*F temperatures. The big difference is a 40*C (104 degrees F) where the AFT viscosity is around 35 cSt and 5606 is about 14 cSt.

For this hydraulic system you want lower viscosity at lower temperatures. This is why I mentioned there could be issues when using ATF in cold temperatures. The ATF will not flow as well and could cause sluggish steering.
 
OK, let me first say that I am retired from Morse Controls, Hynautic Division, mfr of Hynautic hydraulic steering and arch rival of Teleflex / Sea Star at that time. Hynautic sold out to Teleflex, but that is another story.

With that in mind, I present this from the Hynautic manual: (Note the last line)
 

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I'm working on a Lund 1850 Tyee right now with SeaStar steering. My neighbor is a veteran mechanic with the military, Northwest Airlines, and Delta. He was here and looked over the control and spec requirements. He recommended the military spec hydraulic oil that fdrgator mentions. He also noted, there is a difference between hydraulic oil and hydraulic fluid.
 
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