Merc 7.5 gear oil change

[rakos]

My motor has the normal 2 large slot screws at the top and bottom of the shaft, but also a small steel slot screw in the lower-middle.<br />I assume thatI remove the 2 large ones and fill from the bottom; but to what level? Until the small middle screw is reached, or all the way to the top?<br />Thanks<br />John

 

[dajohnson53]

Re: Merc 7.5 gear oil change

Look at this picture and tell us which screws you're talking about:<br /><br /> <br /><br />#36 is the fill screw - It is the lower-most screw, fairly large and is on the lower leading area of the torpedo shaped part near the bottom of the lower unit (straight forward from the prop). <br /><br />#38 is the vent screw, usually smaller than the fill screw. It is just above the horizontal plate that is above the propeller (the antiventilation plate, sometimes erroneously called the cavitation plate).<br /><br />You remove both screws to drain and fill. You fill by squeezing lower unit gear lube into the fill hole and fill until it comes out the vent hole. You then replace the vent screw first while the lube tube is still in place. Then quickly remove the lube tube and replace the fill screw. Make sure you use good/new washers on both screws.<br /><br />On many of these mercs, there is another screw, fairly large, far above these two, high up on the leg just below the engine cowling - usually labeled "flush". This is to connect a water hose to flush the cooling system.

 

[Vlad D Impeller]

Re: Merc 7.5 gear oil change

web page<br /><br />EDIT: oops! it don't work, probably something to do with copywriting laws

 

[Chinewalker]

Re: Merc 7.5 gear oil change

The dime-sized slotted screw at the bottom of the gearcase bullet is the drain/fill. The SMALL, usually round-headed slotted screw located just above the antiventilation plate is the vent. <br /><br />- Scott

 

[rakos]

Re: Merc 7.5 gear oil change

Originally posted by D.:<br /> Look at this picture and tell us which screws you're talking about:<br /><br /> <br /><br />#36 is the fill screw - It is the lower-most screw, fairly large and is on the lower leading area of the torpedo shaped part near the bottom of the lower unit (straight forward from the prop). <br /><br />#38 is the vent screw, usually smaller than the fill screw. It is just above the horizontal plate that is above the propeller (the antiventilation plate, sometimes erroneously called the cavitation plate).<br /><br />You remove both screws to drain and fill. You fill by squeezing lower unit gear lube into the fill hole and fill until it comes out the vent hole. You then replace the vent screw first while the lube tube is still in place. Then quickly remove the lube tube and replace the fill screw. Make sure you use good/new washers on both screws.<br /><br />On many of these mercs, there is another screw, fairly large, far above these two, high up on the leg just below the engine cowling - usually labeled "flush". This is to connect a water hose to flush the cooling system.

http://www.mercruiserparts.com/Show...=160&bdesc=GEAR+HOUSING+(PROPELLER+SHAFT)/URL

 

[rakos]

Re: Merc 7.5 gear oil change

Thanks D and Chinewalker for your replies. It works just as I thought. I am somewhat familiar with gear oil change, having owned a 1969 Searay with OMC stern drive.<br />One more question about the flush screw (top): I am assuming one does not have to drain the water out for the winter. Also, if I wish to start the motor out of the water, is it adequate to put water through a hose into that flush hole, or should I put the motor in a bucket of water? I assume the water intake is at the bottom of the cavitation plate.<br />Thanks,<br />John

 

[dajohnson53]

Re: Merc 7.5 gear oil change

My engine is a '74 9.8, but I believe the following applies to any 9.8 or 7.5 with a flush hole. My owner's manual states that the flush hole is only to be used with the engine NOT running. My understanding is that the water circulates through the powerhead, but not necessarily through the waterpump itself - at least not enough to lubricate the impeller. Therefore, if you run the engine, it has to be in a tank (conventional muffs don't work because of the way the pick up is located.).<br /><br />By the way, you can get an original owner's manual (as well as shop manuals) from mastertechmarine.com. I got original manuals for both of my old engines (OMC and merc) and I find them handy because they give you general maintenance and operation guidelines that are not in the shop /repair manual.<br /><br />As for draining the water for winter storage. Any outboard will drain completely if it is kept in a vertical, non tilted position for a just a few minutes. After that you can tilt it for winter storage. I happen to leave my outboards vertical for storage though, which is probably the most fool-proof way to do it.