2010 Mercury 75 HP Optimax

[StanH]

According to my manual when changing oil in the gear case you fill it untill the oil comes out both holes at the top then put all three plugs back in. On an older Mercury 90 HP (1985) I had it said to fill until the oil came out the top hole then let an once or two drain out before installing the plugs, to maintain an air space for when the oil heated up so the seals did not blow out. I'm just wondering if this air space is not necessary in the Optimax. Maybe they have a vent to prevent pressure build up?
StanH

 

[Texasmark]

Re: 2010 Mercury 75 HP Optimax

I just reviewed the manual for my '02 90 and it says to pull all three plugs, fill till the front overflows, install the screw, continue filling till the rear overflows, install that screw, remove the tube and install the screw. Says nothing about letting some drain out, nor have I ever heard of what you said.

However, it is near impossible to fill without bubbles in the oil and loosing some in removing the filler and installing the plug all of which accomplish the intended purpose. Actually, there used to be only one fill and one drain. Apparently they wanted more oil in the unit causing them to add the second vent hole. So, I guess overfilling is not a problem, nor is over pressure.

Mark

 

[StanH]

Re: 2010 Mercury 75 HP Optimax

The 90 HP I had was a 1985 and only had one fill and one vent hole. The service manual I had for it clearly stated to drain out an ounce of oil after filling.

 

[Dave1027]

Re: 2010 Mercury 75 HP Optimax

I have always thought that the small amount of oil that leaks out before you can get the lower screw back in gives the lower unit the necessary amount of expansion space.