Stern Drive Oil Top-Off

mtp9302

Seaman Apprentice
Joined
Apr 19, 2010
Messages
42
Hi all,

I did a search for this but couldn't find exactly what I was looking for; if it is out there, I apologize for missing it. I've got a Mercruiser 3.7L 4-cylinder, the number on the top is 170 (I've been told it is 170 hp, so I'm not sure if that number is the model, hp, or both). The outdrive, based on what I've read here about identifying them, is an Alpha One.

My post has to do with the stern drive gear oil, and it is probably a very basic thing so please don't laugh too much at the new guy. I was reading about checking the oil in the manual and thought it would be a good idea if I did it, since I bought the boat in April and hadn't checked it yet. Well I somehow missed the part about the outdrive being full up; I had it down, and the oil vent cap popped off real quick and blue-green gear oil started leaking out. It made a puddle about 4" in diameter on the ground by the time I reread the manual and put the drive up.

So now I have a few questions:

1. Did I hurt anything?

2. The manual says that the oil level should be to the bottom of the oil vent hole. It is now not of course, but the manual also says that when changing the oil, you are supposed to add to the oil drain and not the oil vent (to prevent air entrapment). Is this the same story for the top-off I now need to do, or can I simply add to the vent hole until the level it is even with the bottom of it?

3. The manual seems to suggest there is some sort of pump used to feed the oil into the oil drain. I have never used one; what kind of pump is it and where would I get it?

This is probably old hat for your guys, but it is my first boat and I'm learning all the time. Thanks for your help.
 

cr2k

Captain
Joined
Mar 19, 2009
Messages
3,730
Re: Stern Drive Oil Top-Off

There is NO VEnt CAp. Oil should be sealed in the drive.

If you are just topping off, Yes you can add through the "vent" screw.

When changing your drive oil you pull the bottom plug and then pull the top one and the oil will drain. To refill you get the kit from Walmart or your local dealer. It basically has a pump bottle and a screw fitting that will screw in to the drain screw hole. Simply pump it full until it starts out of the vent screw and then insert the top (vent) screw, this will create a vacuum that will hold the oil in while you pull the fitting out of the bottom and reinsert the plug. Be sure to tighten the plugs tight with the help of a wrench on your big screwdriver. Use new drain plug seals too.

If any oil comes out after that, you have a leak.
 

mtp9302

Seaman Apprentice
Joined
Apr 19, 2010
Messages
42
Re: Stern Drive Oil Top-Off

Thanks for your quick help cr2k. Sorry if I used the wrong term, I was referring to the threaded plug near the top of the outdrive on the port side, and it is labeled "OIL VENT".

Sounds like I didn't hurt anything as long I now know to check with the drive up (I'm willing to bet it's not as messy as well). I'll look for the kit also, as I'm trying to learn so that I can take on as much maintenance as I can learn how to perform.

Also sounds like the plugs must be tighter than I thought; I didn't crank too hard from the fear of having the screwdriver slip and strip the plug. I assume you can buy new seals at a place like West Marine or a dealer?
 

ziggy

Admiral
Joined
Jun 30, 2004
Messages
7,473
Re: Stern Drive Oil Top-Off

i don't know where ya get the idea that ya check the drive oil on an alpha1 with the drive up at. ya check it with the drive down and level. when the lub runs out of the vent hole, it's full...

you don't fill from the vent hole. you fill from the drain hole. with a tool like this... http://www.iboats.com/Sierra-Quart-...4807163--**********.693246078--view_id.271179

you should replace the seals on the screws every time ya remove them. be sure and get the old one out. they sometimes tend to stay on the drive and are hard to notice unless your looking for them. some seals are blue, some are yellow. both are ok to use. the yellow ones are the new style. i get my seals from my local mercruser dealer. i haven't looked, but would bet ya can get them from iboats too.
 
Last edited:

liquidlew

Petty Officer 1st Class
Joined
Feb 14, 2008
Messages
304
Re: Stern Drive Oil Top-Off

Yeah, you can get those little gaskets/seals at any marine store. When filling the drive from empty, drive has to be in the full down position. West Marine has a nice pump for that also, I just got a new one there and the part that screws into the drive turns free so the whole hose doesn't twist. Also sounds like you need the manuals for your engine and drive, a MUST have for DIY's!
 

shekinah5678

Seaman Apprentice
Joined
Mar 25, 2007
Messages
41
Re: Stern Drive Oil Top-Off

I'm not sure if all alpha ones are the same or not, but mine has a dip stick on the top of the drive. You are supposed to put the drive all the way down and check to see if the fluid is on the line. I have to jack my trailer up a little to get it all the way down. If I'm just topping it off and not filling it from empty I just fill it from this hole. I'm sure I've read a post or two that say this is ok.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Stern Drive Oil Top-Off

First of all, you should't need to "top off" the lower unit gear lube on an Alpha I or earlier drive without a monitor. If you do, then you have a leak and need to find it fast or you will loose the upper gears due to lack of lubrication.

The ONLY drives with a dipstick was the first 2 or 3 years of the Alpha I Gen II outdrives (91-92or3) after that they went to the reservoir on the engine.

Gear lube monitors on 1990 and earlier drives was an option.
Any outdrive with a gear lube monitor that needs to be continuosly topped of has a leak.
They may burp a bubble of air out of the drive on the first run after changing, but you should never have to keep topping off.
 

shekinah5678

Seaman Apprentice
Joined
Mar 25, 2007
Messages
41
Re: Stern Drive Oil Top-Off

Ya the only time I've ever had to top mine off was after I had the u joints replaced. I just took the drive off and took it to a local marine mechanic to avoid paying for pulling and replacing it. I had just changed the fluid so the mechanic left most of the fluid in but said it would need topped off.
 

mtp9302

Seaman Apprentice
Joined
Apr 19, 2010
Messages
42
Re: Stern Drive Oil Top-Off

Thanks to all for setting the new guy straight. I do have the engine/stern drive manuals to read, but my drive doesn't have a dipstick or oil monitor system. As far as I can tell, the only way to check the oil level is to open the vent.

i don't know where ya get the idea that ya check the drive oil on an alpha1 with the drive up at. ya check it with the drive down and level. when the lub runs out of the vent hole, it's full...

I don't either Ziggy. I re-read the manual and it says to check with the drive (well, anti-ventilation plate) level. I must have looked at it too quickly the first time I checked when gear oil was leaking all over the place. I was in a small panic, so I'm guessing I misread something.

If I'm supposed to check it with the drive down and level, and I did so and oil poured out, this is telling me that my drive was overfull. If so, I'm going to get the drive level and just let it go until it stops leaking out and then I'm at the correct level. Do I understand right?

Also, I've taken the boat out a bunch of times (~ 8 maybe) before I found out I was supposed to check this. It ran fine, but now I'm wondering if I hurt anything by running the drive with the gear oil overfull? Maybe that's why the vent screw popped off under pressure when I unscrewed it?

Thanks again for any help you can give, I'm finding this website and forum to be fantastic.
 
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