lower unit oil level

[sandburr 01]

I have just been given a 1978 20hp Mercury outboard. The motor has not been used in 2yrs. I have changed the sparkplugs and the motor seems to run fine.I have never owned an outboard before and do not know how to check the oil level in the lower unit. Looking at the motor from the rear there are two screws about halfway down the foot. One is plastic and about 1/4" to 5/16" and screws straight in. The other one is metal and maybe a # 8-10 screw and screws in at an angle. Does anybody know anything about this motor?

 

[alcan]

Re: lower unit oil level

Hi Sandburr<br /> There should be two slotted screws. One located near the lowest point on your gear housing (foot) another matching screw will be on the side below the cavitation plate. The oil should be level with the top plug (screw). I suggest that you obtain a manual. They are available at the bottom of the page, you might find one at the library. You will save the cost of the book in headaches alone.

 

[digtech]

Re: lower unit oil level

SandBurr, I'm not familiar with Mercury motors too much, but with most outboards, you drain the oil from the bottom hole and refill in the top hole. It's easier to refill if you put a short length of clear tube on the spout of the oil bottle. Fill until oil runs back out of the top hole.

 

[JB]

Re: lower unit oil level

I have to disagree with Ga Dave.<br /><br />To drain, remove both plugs. <br /><br />Pump oil into the bottom hole until oil runs out of the top. Replace the top, then the lower.<br /><br />Good luck.

 

[sandburr 01]

Re: lower unit oil level

Thanks I found the second screw at the bottom of the foot, I dranined the oil and will fill it up with new. thanks again

 

[Boatist]

Re: lower unit oil level

Sandburr<br />Make sure you fill from the bottom hole until oil comes out top hole. Then put in top plug, remove oil fillhose or tube from bottom and put in bottom plug, just like JB said.

 

[cammydog]

Re: lower unit oil level

Don't forget to change the gaskets on the vent and drain screws. Also, the water pump should be changed, it could be old and dry rotted. Do a search for water pump repair, there is a lot of info in this forum. Good luck!

 

[Chinewalker]

Re: lower unit oil level

One other thing - on most of the smaller Mercs of that vintage, the drain screw is the on that's slotted and about 1/2" in diameter on the bottom of the bullet. The oil vent screw is the small round-head one located further up the gearcase, near the cavitation plate. The plastic slotted screw is for a flush attachment for flushing saltwater motors...<br /><br />Always fill from the bottom - a little messier, but it makes sure you don't get any void bubbles in the system...<br />- Scott

 

[Big Al1]

Re: lower unit oil level

If you fill from the top, you won't know how much oil to put in. If too much, you could blow out your seals.<br /><br />Alan