Fuel System Question

[Beavertail]

Bought a used boat with a 2015 Suzuki DF90A, 140 hours. Wet tested boat before buying and it did fine. First thing I did was replace the fuel/water separator, did not appear to be any water in the filter, but the fuel was a dark color as was the fuel in the small filter on the engine. The oil level in the engine was above full by about a half inch. Did not know whether it was over filled or was ‘making oil’, replaced the low pressure fuel pump, which seemed to be leaking at the plunger/cam follower and changed the oil and filter. The used oil did seem to have a gas smell to it, not completely positive.

So after doing all this and running for about an hour the fuel in the small fuel filter on the engine is now clear and the oil level seems to be holding a constant level.

My question is why was the fuel so dark in the separator and on engine fuel filter? I could understand the on engine fuel filter due to leak back, but how did the fuel in the separator get mixed with oil (assuming it was)? I did not add any fuel during this time, so obviously the entire tank does not have dark fuel.

Any help/insight on this is greatly appreciated.

[Murray]

What if the previous owner dumped fuel stabilizer in the gas tank but DID NOT run the engine after adding stabilizer?

[Beavertail]

What if the previous owner dumped fuel stabilizer in the gas tank but DID NOT run the engine after adding stabilizer?

The filter gas cleared up, so why would the unstabilized gas turn dark? I ran the engine for almost an hour after the fuel/water separator change, but before the low pressure pump change and the fuel was always dark, just thought that maybe an additive had darkened the fuel at first. But then it cleared up after the pump change, so the tank appeared to not be the issue.

Now wondering if the clearing up means it is full of water, will have to check.

[Harper]

When I first bought my boat and motor new, 10 years ago, I filled the 60 gallon tank with ethanol-laced fuel, E-10. By the time I emptied that tank, the fuel was a weird orange color. It still ran fine, but I've never used E-10 again. I always use ethanol-free gas. I've never seen that darkening again. Not conclusive, I know. But I stay away from E-10 on the boat for other reasons, too.

[Murray]

If you ran the engine for an hour and had water in the fuel it should have shown up in the water separator. As fuel ages without any stabilizer it will darken over time, the older the fuel the darker it gets. Fuel with stabilizer will also darken over time just a lot slower. Stabilizer shouldn’t change the colour of the fuel. If you add one drop of red food colouring to one ounce of water then the water will turn red however if you add one drop of red food colouring to say 20 gallons of water the water doesn’t change colour since the dilution ratio is high. When you wet tested the boat you would have noticed water or fuel that is old enough to affect performance. The engine would have ran like crap with the application of throttle. Syphon some fuel from the tank in a clear container and have a look. I purchased a boat that sat for 3 years, the fuel in the tank was the colour of an light lager while the fuel in the VST was almost black. The previous owner had added stabilizer but didn’t run the engine long enough to get the stabilizer through the entire system. I drained the entire fuel system and went with fresh fuel that is ethanol free. As far as your fuel clearing up after you changed the low pressure pump I can’t answer that. If your not sure of the fuel condition drain the system and replace with fresh.