www.iFourWinns.com

Oil in the outdrive will never get dirty, it's sealed. Unless a seal breaks and lets dirt in it should always be clean. You change it because the oil breaks down loosing it's viscosity and it's ability to keep the metal parts from contacting each other causing wear. The gears chop the oil up much like in a blender.

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1981 Columbia 8.7
2015 Yamaha FZR - 87mph - sold
2006 Yamaha GP1300R - sold
2003 Chaparral 215 SSI - sold
2009 Stingray 195CS - sold
2000 Four Winns H180 - sold
1976 O'day Daysailer II - sold
Rick's Four Winns H180 Mods/Upgrade Thread

Even if you don't change it, at the end of the season it's not a bad idea to crack the drain loose a bit to see if any water comes out. That is the main problem with gear oil for sterndrives.

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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