The way I found leaks on my engine was the following:
- Speay degreaser all over it (taking care not to saturate your electronics, distributor, or wiring harness connections) and let it soak for a few minutes.
- then, use a spray nozzle on the hose and spray it off clean. Be extra sure to get the area near and around the valve covers, and especially inbetween the exhaust manifold and and valve covers. A lot of times, leaky valve covers that have loosened up nm over time or bad gaskets end up seeping oil out of the valve covers and it ends up running down inbetween the manifolds and runs everywhere and ends up looking like leaks in various other places.
- Now that the engine is decently clean, dry it off as well as you can or let it sit a day or two to dry off. Then, put a piece of large cardboard under the engine. Make sure the cardboard is wider than the bottom V of your bilge, so that way you can keep it up outn if the normal bilge water.
- Come back after around 48hrs and see if you have any oil leaks showing up on your cardboard. Wherever the drops may be, you can then investigate and look directly above them (use a a mirror on a stick to see those hard to get to areas) and trace the leak to its origin.
Note: It is very normal to have rainwater, overspray, and etc all in your bilge, and its common to have a stained or dingy look. The stained look comes from years of various fluids, leaves, dirt/debris, rust flakes, and tons of other stuff that ends up retouching the bilge or running into it. Grease, oil, and etc is VERY good at holding onto the bilge bottom and will cause water discoloration for years if not thoroughly cleaned originally. As long as that bilge water doesn't smell straight up fuel, oil, or etc, them I'd assume it's just water that's collected in the bilge.
To clean my bilge, I used a heavy concentration of dawn dish soap and hot water. A little scrubbing with a bristled brush, and it looks good as new and I no longer have that odd color of water in there. (My boat is am 84' Sportcraft 250 that had decades of neglect when it came to meticulous cleaning. That's decades of fish guts, grease, oil, dirt, gunk, and God only knows what else, all dirtying up the bilge. So, I'd assume you're in the same boat I was at the time, as my bilge water looked very similar to the color of yours.)
Also, keep in mind, if there's any non stainless hardware, screws, or other things under the deck (like gas tank mounts and other screws and hardware) they're 99% surely rusted up, and any water that runs down those or past those types of things will take some rust particles right with it and DEFINITELY murky up otherwise clean water.
I know it's a long post, but figured I'd be as helpful as I could in case anyone else reads this in the future.
