Is it possible to put too much gear oil??

TheFaMnTN

Cadet
Joined
Jul 30, 2009
Messages
6
I changed my gear oil last night. Unscrewed bottom plug, then unscrewed top plug to get full flow. I put the hand pump for the oil in the bottom drain and filled and purged until I saw no more black coming out the top, only blue. (using Mercury high performance) I then put the top plug back in, NOT ALL THE WAY, gave a couple more pumps of the oil to make sure it was full and screwed the top plug all the way to seal.

I then unscrewed the hand pump fitting from the bottom to put the plug in, but oil gushed out like it was under too much pressure, instead of drizzling out like I thought it would with the top plug in. I screwed the bottom plug in quickly.

Has anyone ever heard of having too much gear oil? If so, should I open the bottom plug to let a little more drain out?

Thanks in advance for any suggestions.
 

bustermin

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Apr 13, 2009
Messages
315
Re: Is it possible to put too much gear oil??

I do it the same way, with the exception of the last few pumps. when you did that you added pressure to the oil in the lower unit so when you removed the fill hose it had a way to release the pressure. I usually pump until i have clean fluid coming out the top then install the top plug pull the hose and install the lower plug and thats it. The reason for filling from the bottom is to remove the air from the lower unit. i would think the way you are trying to do it can only result in a blown seal as it will start under pressure and it need to get out somewhere, it is common for the seal on the fill/drain plug to leak from pressure coming from hauling the vessel down the highway during the heat of the day and then dunking the lower unit into cold water. the pressure needs to get out somewhere and better the little seal around the fill/drain plug then one of the major seal for the lower unit.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Is it possible to put too much gear oil??

if you do it properly no it is no possible.
Changing lower unit oil

There are 2 straight slot screw on the starboard side of the lower unit. Top is vent plug, bottom, drain and fill plug. ( do not touch Phillips head screw).

Remove the bottom plug, put container under lower unit, now remove the vent plug, while the oil is draining, replace the seals on the plugs part # 311598, buy several of these, ( they are a one time use item)

Walmart and many places sell a little hand pump. To use to fill the unit, you insert the tube into the bottom hole, and pump till oil reaches the vent hole. Install the vent screw, then remove hose, install the drain-fill screw, clean up mess.

The screws can be hard to get out, do not mess up the head. You may need to employ an impact screw driver to break them loose.
 

Rick.

Captain
Joined
Jul 30, 2006
Messages
3,740
Re: Is it possible to put too much gear oil??

The two more pumps was not necessary however two pumps on that pump is not much oil so I would not worry. Was your top vent plug screwed in tight before you took the hose off the fill hole? If not that would be why the oil came out so fast. The top plug should be tight before you attempt to put the bottom one back in. Best of luck. Rick.
 
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