75hp 1975 lower unit oil check/change

[everhart57]

okay so I want to change the lower unit oil so I'm reading on here and it's kind of scarring me... I thought I knew what the drain and vent plug were but some other screw is in there too that you should never remove? how do I know I'm on the right one? next, I pulled out the vent screw to check it with a piece of wire as some site said to... the oil is a little cloudy but not discolored. What does this mean? It still looks yellowish clear just a little on the cloudy side. If that means its leaky and I don't have a pressure tester should I just replace the seals and check it again after running it? I'm going to take care of everything at the end of the season, impeller and all, I just want to change the oil for now since i don't know when it was last done.

 

[Frank Acampora]

Re: 75hp 1975 lower unit oil check/change

On your engine: Up above the cavitation plate there is the vent screw. Below the gearcase torpedo, on the side of the skeg, at an angle, is the drain screw. Both these screws are 3/8 X 16 with a large slotted head about 9/16 to 5/8 diameter.

On the side, toward the front of the gearcase torpedo, is a smaller recessed screw. This is the shift pivot and should never be removed unless you are disassembling the lower unit.

Since oil floats on water, checking the lower unit lube through the vent screw will not give a true indication of condition.

To check, you remove the bottom drain screw and loosen the upper vent, allowing only enough air in to let the oil dribble out. If free water comes out first, then for sure you have a leak. If milky oil comes out then there is water in the oil too. Milky means just that: Looks like cafe au lait. If clear or semiclear, top off the oil and run the engine.

To refill after draining oil: With both screws out and the engine vertical, fill with oil from the bottom (drain) screw hole until oil comes out the vent. A cheap hand pump available at auto stores helps here. Replace the vent screw and tighten snugly. Now remove the pump nozzle and quickly insert the drain screw. Wait about a half hour to let air rise then repeat the process without draining to top off the oil. Tighten both screws really well. Use a large screwdriver.

Note that depending upon condition, you may or may not need to replace the screw gaskets. Note also that frequently, the gaskets will stay stuck in the recess for the screw head. If this happens, don't think it is lost and add another on top.

 

[recon6606]

Re: 75hp 1975 lower unit oil check/change

"On the side, toward the front of the gearcase torpedo, is a smaller recessed screw. This is the shift pivot and should never be removed unless you are disassembling the lower unit."

Many thanks for this useful post, Frank. However, I read it too late. I bought this 78 16 ft Cobia with a 76 75HP Chrysler. I promised my 5 year old grand-daughter that I will take her water sledding last year and she held me to it. So on the 4th of July, we went. The boat rides well and the engine seems OK. I am slowly refurbishing everything that needs to be done.

I wanted to check the gearcase oil and read your post too late: I removed the shift pivot screw. After I read your post, I put it back. Nothing else was touched. I hope I did not do any damage. Please let me know how to proceed.

I found the drain plug and a small amount of clear water came out followed by a milky fluid. I am going to replace the gearcase oil as per your instructions.

There is another opening near the cavitation plate about an inch below the vent hole. A small amount of dark brown grease is oozing from it. What does this mean? What is the hole for.

One more thing. In my attempt to clean the motorhead which was filthy (I could not find the ID plate until after the clean-up), I hosed the gunk down. I noticed that some of the water dripped down the exposed shift rod. Again, did I do any damage?

Thanks.

Nick

 

[Frank Acampora]

Re: 75hp 1975 lower unit oil check/change

Outboards are meant to be in water! Short of spraying it directly into the carbs, you can not do much damage.

As far as the shift pivot screw, if the engine will shift into forward and reverse and return to neytral then you need not worry. The small hole is a leg drain and frequently unburned gas and oil will dribble out it.

Now, if you did have free water in the gearcase, after refilling it, check a couple of times. Free water plus milky oil indicates a leaking seal somewhere. It could have been loose plug seals so that it why you check it. If after you replace the oil and fully tighten the drain and fill plugs you still have milky oil upon running the boat, then it is time to check the seals.