50 hp merc runs perfect but,

[Niagara Mike]

I just want to know how to check the gear oil in the lower unit,, and make sure it all good down there, ? Its a 70's - 50hp merc thunderbolt.

Its runs very nice and I just want to make sure it stays that way.

thanks guys!

 

[Jake.]

Re: 50 hp merc runs perfect but,

How to check it or what to look for? To check it simply unscrew the fill screw which should be at the bottom of the lower unit, normally in front. There is another screw about the same size that is above the fill screw that allows the lower unit to vent. Unscrew this as well to allow all the oil to drain. Inspect the oil for water, metal shavings, discoloration, etc. If none found, refill lower unit and you're good to go.

 

[Chris1956]

Re: 50 hp merc runs perfect but,

It is not useful to check the gear oil. Just change it at least once/year. It sounds like you have never changed it, so this would be a good time to do so. Use any marine gear oil for mechanical shift motors. Buy a quart, and pull the two stainless steel plugs and let the old stuff drain. Now squeeze the bottle into the lower hole until it emerges from the top hole. Install the top plug with a new gasket. Now remove the gear oil bottle and install the bottom plug with a new gasket. Make the plugs tight. I usually use a hand impact driver to tighten them.

 

[Niagara Mike]

Re: 50 hp merc runs perfect but,

Ok yeah.... I just want to make sure it all good as you are right I have never done it. I just got the boat, re did the transom and put it in the water, the guy I got it from said he gave it a tune up and got it water ready but he was shady and I have zero trust.,

Thanks for your help BTW

I have one vent that says flush and one a bit lower that says vent.

Where do I buy new oil to refill it?

How much do I need?

 

[charlie741]

Re: 50 hp merc runs perfect but,

Flush is for water. Vent is the upper plug referred to earlier. look lower to find the drain, bottom side of the prop shaft "housing"

 

[hotrod53]

Re: 50 hp merc runs perfect but,

Buy yourself a hand pump, they are cheap (about $12) and will screw right on top of a quart bottle and into your fill fitting. Your 50hp, if like my '77 500 Thunderbolt, takes less than a quart. Pump it up thru the bottom hole till it comes out the top hole, then put in the top plug. Installing the top plug creates a vaccum that will keep the oil in the unit till you unscrew the pump and screw in the bottom cap.

They sell a squeeze tube of lube, they are the exact amount that the unit takes. IMO, the pump is the way to go and you'll have enough left to do it again next time.

 

[fisherguy123]

Re: 50 hp merc runs perfect but,

I bought a 1982 merc 50 last year and never used it until this spring. First thing I did was drained the lower end gear oil and almost crapped when the oil came out with water in it . I thought I would have to change all the lower seals but I took a chance and changed the fluid and the gaskets on the screw plugs. After a tank of gas I drained the fluid again and no water this time....lucky for me it was the old gaskets that the previous owner had neglected to change when he changed the oil that were leaking......so be sure to change the 50 cent gaskets everytime you change your oil.....it may save you a bundle in the long run !!!!

 

[Niagara Mike]

Re: 50 hp merc runs perfect but,

Thanks for all the advice guys, Im going to change the oil this weekend after I buy some rubber gaskets!