www.iFourWinns.com

So what is the best gear oil to use in the OMC Cobra, Evinrude HPF Pro or Mercruiser High Performance gear oil? Last summer about mid season I had to have the oil changed at a marina due to the oil dipstick coming loose (noticed sheen of oil after a run), and they put in the blue Mercruiser oil. End of the season last year per recommendation of local marina I changed the oil with Evinrude HPF Pro. So as I am winterizing the boat this week I drained the oil and noticed the remnants of the Mercruiser oil actually separate from the Evinrude HPF. Debating if I should just drain the HPF out and stick with the Mercruiser now...

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2008 H200 Frenzy Edition 5.0 GXi

1993 Horizon 190 5.0 EFI (Sold)

I've been using the Merc stuff in mine for 10 years with good results...

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Either option would be fine.
Marine gear oils won't really suspend that much water contamination anyway, so also consider an automotive 'performance' GL5 75w90.

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2011 Four Winns H180 SS.
Aussie built Mustang 2800.
SOLD - 1997 Four Winns Horizon RS

I used the Merc Hi perfromance in our OMC King drive and continue to use the same in our Volvos with good results.

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"One Moor Time" 2006 288 Vista
"Kalin II" 1995 258 Vista
"Kalin" 1985 Four Winns 215 Santara