Confusing marine power steering specs

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Jun 19, 2021
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I have a power steering system in a 52' boat. The manufacturer SeaStar has a strange history regarding fluid requirements. The system consists of a hydraulic pump (Vickers V10), a steering ram (SeaStar HC5803), and a manual hydraulic pump (Capilano 1250V) connected to the steering wheel. There is also a reservoir and filter. Seastar's manual states that if the helm unit is "Seastar" then one must use fluids meeting spec MIL H5606C, but in case of emergency it is OK to use Dexron II (it's an old system). They emphasize that you must flush out the Dexron II and replace with the proper fluid soon thereafter. However, strangely, if the helm unit is "Capilano" then one must use Dexron II. Then, in 2018 the parent company for SeaStar changed from Teleflex to Dometic, and they promptly issued a statement indicating they now only approve their own oil (at $90/gal) due to "upgrades in some of their components". Suspecting this might be a profit grab, I looked up the specs for the Vickers V10 hydraulic pump and they aren't even matched by the original fluid spec. Vickers states "Pumps can be used with anti-wear hydraulic oil, or automotive type crankcase oil (designations SC, SD, SE, SF, or SG) per SAE J183 JUN89...The viscosity range of petroleum oil, with the pump running, should be 13-54 cSt (70-250 SUS). The oil viscosity at 38° C (100° F) should be 32-48 cSt (150-225 SUS)." Looking at some Mercon/Dexron III, typical values are 35.67 cSt at 40C, 7.38 cSt at 100C. This would seem to satisfy the viscosity requirements of the pump ( I have not measured it but the steering fluid has a cooler and likely does not get above 70C). However, examples of oil meeting MIL H5606C (Chevron Aviation Hydraulic Fluid A) has 15 cSt at 40C and 5.5 cSt at 100C. I have not measured it but the steering fluid has a cooler and likely does not get above 70C.

I worry that SeaStar is being arbitrary about their oil requirements. I am considering using Dexron III ATF as per their old recommendations, particularly since this appears to match the requirements of the Vickers pump which is the only high wear items in the setup. I am not an oil expert, so to the experts here I ask what other concerns I should have about using ATF here (or any of my statements made above).
 
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My buddies boat had the same seastar setup you described. We went to the local airport (non commercial) and bought a gal of the Chevron Aviation Fluid. It was not cheap but it was less than half of seastars stuff. I am sure there is a reason but just looking at the system I cannot figure out why any good hydraulic oil that met the viscosity requirements would not work. It is a real simple basic system even with the autopilot.

Edit: Maybe it has something to do with exposure to salt on the ram arm but I am not aware of an additive that would negate salt intrusion.
 
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boater

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Jun 19, 2021
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Samven, thanks very much for your answer. I feel the same way. The thing is the Chevron Aviation fuel is too thin for the Vickers power steering pump. And I trust Vickers more than I trust Seastar to know what is good for the Vickers pump. Was your pal's boat with power steering? My power steering runs off a shaft driven power take off bolted to an 800 hp CAT engine.
 
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Sorry Boater, no his was on a 33 intrepid. It had hydraulic but I thought the Auto Pilot was driven by a pump. Nothing like yours, sorry.
 

boater

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Jun 19, 2021
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Got it. Yeah, the autopilot pump is a relatively minor affair. The Vickers pump is capable of delivering 2500 psi at 6 GPM. It's a rotary vane pump, so the vanes scrape against the pump chamber walls and the oil film is the only thing keeping that pump from burning up.
 
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