Replacing lower unit oil procedure

[erosenwinkel]

I have drained the lower unit oil overnight. I have a fill screw and a vent screw horizontal to each other a few inches apart. I posted a while back and was instructed to keep the motor vertical while refilling and then let the air bubbles come to the top and then top off. If I trim the unit up to a 45 degree the vent hole will be higher than the fill hole and I will be able to get more oil in. Is it possible to overfill and cause damage? This is my first time at performing this procedure and I want to do it properly. I read on some other posts that you are supposed to fill the oil through the drain hole in the very bottom, can someone please clarify. Force 125hp (1258x5a) Drained oil looked black with slight hint of grey (more black), not milky. Thanks in advance, Eric

 

[Frank Acampora]

Re: Replacing lower unit oil procedure

If you are talking about filling then tilting: Yes, it is possible to tilt to 45 degrees and get more oil in. Yes it is possible to blow a seal from too much oil.

If you try to fill with the engine tilted, the air will be trapped at the prop end of the gearcase and you probably will get less oil in. --I don't know; I never tried it.

On your engine you fill through the fill hole and let air escape from the vent hole with the drain hole plugged.

Don't overthink this simple procedure--Just do it the factory way with the engine vertical.

 

[Poncho Villa]

Re: Replacing lower unit oil procedure

Great thread! I had much the same confusion as the OP. My Seloc manual mentions something about filling the lower unit via the drain hole so something wasn't adding up. I appreciate the question and Frank's response. Indeed I overcomplicated the procedure in my mind.
Thanks again!

 

[erosenwinkel]

Re: Replacing lower unit oil procedure

Not trying to overthink a simple procedure. Just trying to perform a simple procedure correctly for the first time. The manual that I have explains the procedure as "fill the lower unit with the appropriate viscosity oil"

 

[Rugid]

Re: Replacing lower unit oil procedure

You will want to fill through bottom hole to allow the air to escape out the top hole. You can get a lower unit pump at most marine stores for 10.00 or so. Once you have it filled ( so the gear oil just starts to come out the top ) let it sit for aprox. 1/2 hour. Then top it up. Don't forget to pressure test it.

 

[erosenwinkel]

Re: Replacing lower unit oil procedure

Pressure test it? Nobody or nothing I have read said anything about pressure testing. If I have to, HOW and with what? Please be very specific, this is my first rodeo.

 

[Frank Acampora]

Re: Replacing lower unit oil procedure

There seems to be some confusion: On engines that have three plugs you fill through the fill and vent through the vent with the bottom drain plugged. On engines that have TWO plugs, you fill through the drain until oil comes out the top vent. ALL Force and post 1978 Chrysler engines over 70 HP have three holes: Drain, Fill, and Vent. SOME engines less than 70 HP have only two: Fill and drain. Chrysler engines with the pre-1978 two piece lower unit have only a fill and drain. SO: We need to specify which engine we are working on to specify the correct procedure.
If the original oil did not show contamination with water, since you are not removing any components or changing any seals, it is not absolutely necessary to pressure test. You just assume that it was holding oil without leaks so it should still do so. Just check the oil after a couple of runs to see if it has water contamination. If it does show water, then pressure test to see where the leak is.

Pressure testing is a very good test of the lower unit seals before re-filling with oil and if seals have been replaced it is, or should be, considered mandatory.