Lower Unit Oil Question

[marshall256]

I have a 2004 225 HP Mercury Optimax (Regular OPTI not Pro XS). Serial number is 0T847131.

I just drained my lower unit oil and it is Jet Black (no green hue) and smells strong like burnt oil. It has a modest amount of fine metal particles visible. It looks like a black metallic paint almost.

I doubt the motor has 15 hours on it since the last time I changed the lower unit oil.

Motor runs smooth with no unusual noises. Although, I have been chasing a 200 RPM loss at top end. The motor was completely checked by a local certified mercury mechanic and the power head is in top notch shape with everything within spec (compression same on all cylinders also). They didn’t check the lower unit. I actually seem to feel like an added drag in the engine around 5000 RPM that seems to prohibit it from reaching my normal 5700 RPM’s. Prop is also fine, but to make sure I sent it back to Croxton for a repair and cleanup which made no difference.

Just wondering if the condition of the oil and given loss of RPM’s warrant dropping the lower unit and digging further into th LU?

[OldTimer57]

seems to turn black as it is run. Main things you don't want are lots of metal filings (some are unavoidable), any signs of water intrusion. Can't avoid the stink.

[Savage]

Digging into the lower unit in not a DYI job. Was the gear lube that was drained Genuine Mercury High Performance Gear Lube?

[DewRonInc]

Just ran it too long i bet, run it a bit, change again, bet it will be fine.

[DewRonInc]

Change with merc oil also as said above , i like high performance oil myself

[EuropeanAM]

High Perf (Mercury or Quicksilver) is the best way to go.

More information can be found in the FAQ Section (LOTS of useful posts covering maintenance, oil, batteries, fuel, common problems, etc).

[Ben Danbleume]

Just ran it too long i bet, run it a bit, change again, bet it will be fine.

15 hours is too long for lower unit oil?

[fishnfireman]

15 hours is too long for lower unit oil?

hope not !!

If it was mine I would change the oil and run it a few trips then drain and inspect oil.
It's been my findings that once a LU is broken in good, the metal fillings are very minimal !!
From your report about metal filings and loss of top end RPM I would be suspect also.

[marshall256]

170A1AED-05CF-44E8-89C7-0E6D7B3FEBE4.jpeg

Quicksilver High Performance is what I used.

[marshall256]

No sign of water intrusion. Metal particles settled overnight. I ran a tongue depressor through the bottom of my pan and any particles found were relatively fine with no large chunks found (Yet).

I may just refill and go run it a few times. Then drain and check again.

[Bamaman]

And sometimes we must take the time to have the lower unit professionally pressure and vacuum tested to make sure the seals are okay.

[fishnfireman]

And sometimes we must take the time to have the lower unit professionally pressure and vacuum tested to make sure the seals are okay.

Although a good idea, I see no evidence of a leak issue from the OP's description.