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BF225 Flushing and cleaning Lower Unit before refilling with new oil?

M

maxthrottle

Contributing Member
I replaced the ruined lower unit on my port 2006 BF225 last summer. Even though both engines had only 20 hours or so since the lower unit oil was changed since it was hauled out, I noticed the oil in the older starboard engine lower unit was thicker, darker and had a streak of gray paint. The oil from the new lower unit looked...brand new. I've also noticed that the engine with the new lower unit does run quieter than the original 15 year old starboard engine.

My question is this. Can cleaning and removing the ancient reside inside the lower unit gear case make a difference? Will the engine perform better or quieter? Has anyone done this successfully? If so could you recommend a procedure to flush the lower unit before refilling it with new oil?

Thanks, Bob
 
Well...

The "streak of gray paint" indicates water intrusion into the gearcase. That gray color is what the entire load of oil will turn after enough water gets churned into it. You should probably air test the housing to look for a bad seal.

Depending on how long the oil has been getting diluted, you might have some bearing damage in there and you could be looking at some repair problems on that transmission too. It could explain the roughness and noise you describe.

Notice I say MIGHT and COULD because I'm just speculating here.

To answer your flushing question, it's not something that is typically done in my experience but I don't know as much as many others here.

If I were to attempt it I would use a solvent that was likely not to harm the bearings and that would completely drain out. A mix of transmission fluid and diesel fuel comes to mind.

And, just like doing a gear oil change, I would add the solvent via the drain hole with the fill plug removed. When I saw fluid exit the fill hole I would replace the plug and add (UN-like doing a gear oil change) an additional amount of solvent in an attempt to fill the housing. CAUTION would be necessary when doing this as to not apply any artificial pressure to the seals while doing this "overfilling".

This will be a pretty messy exercise.

I would NOT start the engine but I might choose to put the outboard in gear and "hot jump" the starter to mix things up.

Again, I HOPE I've used enough "might" and "maybe" indicators to convey that this is all speculation on my part since I've never flushed one.

In reality, rather than flushing, I would probably just remove the transmission and inspect, clean, repair or replace AND clean the housing because that is something I HAVE done in the past. Just not on a 225hp.

Good luck.
 
jgmo said:
Well...

The "streak of gray paint" indicates water intrusion into the gearcase. That gray color is what the entire load of oil will turn after enough water gets churned into it. You should probably air test the housing to look for a bad seal.

Depending on how long the oil has been getting diluted, you might have some bearing damage in there and you could be looking at some repair problems on that transmission too. It could explain the roughness and noise you describe.

Notice I say MIGHT and COULD because I'm just speculating here.

To answer your flushing question, it's not something that is typically done in my experience but I don't know as much as many others here.

If I were to attempt it I would use a solvent that was likely not to harm the bearings and that would completely drain out. A mix of transmission fluid and diesel fuel comes to mind.



And, just like doing a gear oil change, I would add the solvent via the drain hole with the fill plug removed. When I saw fluid exit the fill hole I would replace the plug and add (UN-like doing a gear oil change) an additional amount of solvent in an attempt to fill the housing. CAUTION would be necessary when doing this as to not apply any artificial pressure to the seals while doing this "overfilling".

This will be a pretty messy exercise.

I would NOT start the engine but I might choose to put the outboard in gear and "hot jump" the starter to mix things up.

Again, I HOPE I've used enough "might" and "maybe" indicators to convey that this is all speculation on my part since I've never flushed one.

In reality, rather than flushing, I would probably just remove the transmission and inspect, clean, repair or replace AND clean the housing because that is something I HAVE done in the past. Just not on a 225hp.

Good luck.
Click to expand...

Thank you for your response. The Honda shop pressure tested the the lower unit last fall and it was tight. I've never seen any obvious evidence of water. This oil was mostly golden color just not pristine like the oil drained from the brand new lower unit on the other engine. I'm thinking there maybe 15 years of residue in there somewhere and if it would be better to give it a good cleaning rinse before refilling again before putting it in the water. I may be better of leaving it alone just drain and refill and was wondering if anyone has had success flushing the inside of a lower unit before and if it was worth the trouble.
I was going to research a Gunk type product.

Thanks,
 
You have to consider that there is nothing going on inside the case except differing forms of friction and possibly slight "sluffing off" of materials from the gear teeth and clutch dogs. Most of that wear actually occurs during break in.

If the two lube oils were identical going in, then having one one seem "thickened up" and discolored after only 20 hours would, indeed, concern me.

However, I am a big fan of "if it aint broke (yet) don't fix it" and tend to agree with you about just changing oil again and keeping a weather eye on it.

Good luck.
 
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