This is full hydraulic in enclosed canopy race boat.
Thanks
Steve

Steve,

160-180F is normal operating temp for Power steering systems. Most power steering fluid is not capable of running much hotter than that without breaking down. There is not a lot of controls in the industry for requirements for power steering fluid. Most of the off the shelf auto parts store stuff is junk. I have always run Type"F" ATF in my pleasure and race boats with a small cooler on the return side per Brett May (Mayfair) and Steve Everett (Zeiger Performance).

how do you know this?the op did not say that.

looks like the op answered that question.

I'm betting merc would not spend the $$$$ to put a P/S cooler in the system if were not needed...

imo,mercury did not install a ps cooler on most of their engine&drive packages because they did not need them.

I have a standard Merc PS pump with Latham assist. Took the Merc cooler off and bought a 6x8in tranny cooler for the return line and mounted it in the gunnel. After hard runs the copper line is only luke warm. I run the Synthetic Mobil 1 tranny fluid. It is bright red and crystal clean in the Latham reservoir like the day I put it in so its definitely not breaking down or getting too hot. I honestly dont think I even need the tranny cooler for my application.

I agree. I just rebuilt a 1980 288 Mercruiser for a customer and it had a cooler.

Yes however most are utilizing synthetic fluids these days that are capable of much higher temps and extended use(their main selling points). It surprises me that they recommend Type F, as it is void of friction modifiers,which fluids such as DEXRON contain, however friction modifiers have zero impact on a hydraulic system, so either may be used. ATF is a great hydraulic fluid as it is shear resistant and a 20wt oil. A common myth is that transmission fluid has large amounts of detergent. This is false for anyone wondering.

Have you verified these stated temperatures in a boat equipped with a cooler? They look almost identical to OEM stated fluid temps in a passenger car. IMO the op should verify temperatures. Plenty of boaters run without a cooler. Again without DATA this is all up to this point here say. Not calling you out, however stating most autoparts ps fluids are substandard is a pretty steep claim with no data to backup that statement. If you don't have used oil analysis to verify this statement, it's just your opinion, or someone else's, and I don't care if that happens to be a aftermarket manufacturer or not. Oil cannot be judged by smell or color. Analyzing a fluid is the only way to truly know.

Granted this is automotive, however almost all of the components in a mercruiser application are automotive based parts with no special deals etc..
http://www.turnone-steering.com/Powe...-FAQs_b_2.html

If you use a good quality synthetic ATF or PS fluid that's proven capable (with UOA's), 275 degrees is the upper limit. All bets are off using a hydraulic add on system.

I'm not seeing that there is no way mine is that hot even if the fan is off. Since this has become a topic again, I will take the hand held laser thermostat and shoot the lines the next time I am out. I can grab my lines after a hard run and they are nowhere near burning me.