F250 lower unit oil

[JackintheBoat]

I had to replace the counter rotating lower last spring. Changed the oil out after 20 hours for the break in then again at 50 hours and just did it this weekend at another 50 hours. The first 50 hour change noticed the first few ounces of oil it was dark brownish in color then the rest of it was green, no signs of water or metal shavings. This very last change all the oil was dark brown in color, again the consistency was fine and no signs of metal shavings whatsoever.

I have read where the counter unit works harder and has less capacity for oil so it breaks down sooner turning the color darker, thus the reason to be doing it every 50 hours. I am going to remove the lower and have it pressure tested anyways, but just thought I would get some feedback on this dark brownish color.

thanks

[pstephens46]

Not sure if you have an issue. I have used synthetic oil in my lower unit that turns darker after use. Oddly, the non-synthetic versions seem to remain the original color. I have no explanation and not concerned either. You can buy a Mity-Vac pressure tester for about $35.00 if you would rather do this test at home. I splice in the little metal oil adapter that fits the Yamaha lower unit. Take 5 minutes after draining the oil.

[JackintheBoat]

ok thats a good idea. So, I drain the oil and plug in the pressure tester to the bottom or top drain plug or does it matter? And what PSI for what amount of time would you say I am looking for? And I do not have to remove the lower unit do i? thanks for the help

[fairdeal]

FWIW the service manual shows the tester in the top - makes sense because even "empty" of fluid, you are going to get a few dribbles out the bottom -

why not avoid the mess. You don't need to remove the LU.

My F225 manual says it should hold 10 psi "for at least 10 seconds"

Turning from light clear to dark - but still "translucent" has happened to me, too - sometimes, but not always.

Don't have an explanation.


IMO so long as your oil was not "milky" - you do not have a significant amount of water ingress, hence, no appreciable leak.

[JackintheBoat]

so I drained the lower oil (all but about 5 ounces), hooked up a pressure tester to the top screw and pumped it up to 14 per the manual. The pressure did not hold and dropped to zero within a minute, so obviously have a leak somewhere. Again, I cant imagine its that bad as the oil color was dark brown, not milky at all, good consistency and no sign of water separation. But I guess enough water to make it brown, dont get that part.

So now I will remove the lower and submerge it in a trash can of water while pressurizing it again to find the leak. If bubbles comes out of the hub then I guess its a prop seal (I do recall having mono wrapped around it at one point but dont remember it being very bad).

If bubbles come from other areas, what seals in particular am I looking at replacing? From what I read its not all that hard, just looking for some direction here once I determine I have a seal thats gone bad.

thanks for the help guys

[pstephens46]

Propshaft seals, driveshaft seals and shifter shaft has a seal also.

You could use soapy water on those areas if you did not want to duck the entire thing,,,, Make sure your connection from tester to lower unit is not leaking also.

[JackintheBoat]

thanks, it makes me think I did something wrong with the tester, I was pretty certain it was connected well. The pressure just fell so quick you would think there would be major water intrusion or oil simply leaking out onto the concrete, neither of which has happened.

[fairdeal]

when I drained this out of my F225 LU



I sprayed soapy water while pressurizing the LU and saw this:

[99yam40]

thanks, it makes me think I did something wrong with the tester, I was pretty certain it was connected well. The pressure just fell so quick you would think there would be major water intrusion or oil simply leaking out onto the concrete, neither of which has happened.

make sure you use new seals for the drain and fill screws also

[JackintheBoat]

ok thanks will try the soapy water on the seals.

so removing the lower looks pretty easy the 6 bolts and the bolt behind the zinc anode and just slide it off.

Assuming I pinpoint the leaky seal and replace it, is there any real trick into putting the lower back on. Its the LH counter rotating unit, I read where it has be in gear, I have fly by wire controls, so would I have to engage the gear on the lower with pliers?

[fairdeal]

so removing the lower looks pretty easy the 6 bolts and the bolt behind the zinc anode and just slide it off.

Assuming I pinpoint the leaky seal and replace it, is there any real trick into putting the lower back on.

I'm thinking 9 bolts total - counting the one holding the anode.

Where did you read that it needs to be in gear? I've only seen neutral...

I doubt it matters, so long as you don't change either the shift shaft or the remote control after you drop it.

DO NOT use pliers on the shift shaft - you risk buggering the splines

Which is btw the "tricky part" of getting it back on.
The driveshaft - generally - goes right into the crankshaft -

but when you've only got about a finger's width of gap left,

you have to reach in and line up the two shifter parts so they mate nicely.

[rodbolt17]

there is a bolt under the anode, a bolt just fwd of the anode and 3 on each side.
there is a shift shaft seal,a shift shaft carrier oring a drive shaft seal set and a driveshaft seal carrier oring.
orop shaft seals and carrier orings.

DO NOT ramdomly decide to use synthetic gear lube.
you MUST make sure your unit has NO bushings and bearings only first.
or use the Yamaha lube chart.

[JackintheBoat]

ok thanks will pull it off tonight and see where its leaking.

My local dealer says its 3 hours labor plus cost of the seals to replace them all, about $400 bucks, so Im hoping its one of the easier seals to do myself.

thanks again

[JackintheBoat]

to answer the part about the gear lube, I used the quicksilver high perf gear lube, used it several times without a problem. I have used the quart bottles of quicksilver you can buy at west marine, etc. I am wondering if I put in the non high performance for the smaller motors by mistake (bottle looks the same) and it discolored to brown from the heat.

IDK, just still stumped by the brown color, complete lack of water in the lower.

[rodbolt17]

if it is a left hand case take it to the dealer.
or tear it up tying to get it apart without the correct tools or training.