I have 2 420 hp's that are 15 years old. I noticed yesterday that I have some oil in the bilge. Its a ring around the water in the bilge. Its hard to say how much is in there. Lets just say its a ring around the bilge. On more than an 1/8 of a cup. I ran the boat for 2 hours at 3000 to 3500 rpm. I know it can be normal for older engines to leak some oil. It is not an apparent leak. I see no trails in the bilge or drips when running the engine with the hatch open? The question is how should I touble shoot it and what should I do about it? Where are the most common places these engines leak oil?? Thanks

Rusty oil pan? Bravo rez leaking? If you have the garbage round rez for Bravo I'll bet its the cause, they all leak at some point.

I don't have bravo I have TRS drives. Also, how do you tell if you have a rusty oil pan?

Try feeling around with your hand .. if you can reach. Or get under there with a bright light and mirror if you have to. Watch the mirror for a few minutes and if it's leaking you'll see the drip.

Also check the drive lube resovoirs on TRS inner transom assembly. I decided to check on service work by marina that was supposed to include topping off all fluid. TUrned out they didn't fill the resovoirs -- so I filled 'em up.

Today I was doing some project stuff and there was lune oil in bilge--everything else was as I left it last weekend so I'm assuming culprit was from filling (or overfilling) those resovoirs.

It started to rain before I could check closely--another project.

Poorsche, now you got me thinking. The only thing I did was fill the transmission fluid levels before I discovered oil in thr bilge. How do I distinguish the difference between transmission and engine oil? Trans is red and oil is clear when new but wouldn't they both be dark in color after they are old???

The lube in the TRS resevoir is bluish-greenish stuff--Mercruiser HP GearLube is what I used. Trans fuid is the red stuff.
I would thing the trans fluid would be real obvious it was in the bilge alone--if it's mixed with the gear lube--not so obvious.