Fuel separation and water

Southern Pirate

Active Member
Nov 17, 2019
Boat Info
2005 sea ray 270 amberjack
5.7 Mercruiser w/Bravo III Drive
I replaced the motor on my 2005 Amberjack recently. Everything seemed to be going great. While on the hose, the motor started fast and ran very well. I was finally able to take the boat out to the lake and this is where I found problems. The motor ran good at idle speed and handled well. It was when I increased the throttle that I ran into problems. Anything over idle speed and the boat would lose power and start to shake really bad. I pulled the boat back out and again, at the house, I could find no problems. While on the hose everything was normal. The motor would rev up without a problem and when placed in gear, the drive was fine. I put the boat back in the lake and it idled fine but upon increasing power, it would drop RPMs and start to shake. I brought the boat back home and started to scratch my head. Since the motor is a closed cooling system, I knew the problem had nothing to do with lake water. I then decided to check the fuel. I put my fuel pressure gauge on the fuel rail and everything was normal. I watched for leak down but did not see any. I then started the motor and after a tiny dip in pressure it came back to normal. I revved the motor and it had small dips in pressure but recovered quickly. So this ruled out fuel pump and pressure problems. I then went to bleed off the pressure to remove the pressure gauge. I had a small Ball jar and released the pressure into the jar. I capped it and placed it on the deck and put everything back to normal. As I climbed out of the engine compartment, I picked up the jar and noticed a small separation in the little amount of fuel in the jar. I went back down in the engine compartment and reconnected the pressure gauge. I built up fuel pressure several times and relieved it into the jar. Sure enough I had a small phase separation, not much but it was there. My fuel gauge showed about 30 gallons of fuel but it was fresh and non ethanol fuel. My guess is, I still had bad fuel left in my tank. I found a place to put the boat on about a 15 degree incline and I disconnected the fuel line and connected an electric fuel pump to the line. I then was able to pump out almost 1 1/2 gallons of bad fuel. As I pumped, I did not see a separation until I started on the second gallon. I then pumped until I got a full gallon without a separation. A friend of mine recommended a product call K100. I ordered it and I am waiting for it to come in before taking the boat out again but I think that the separation of fuel was my problem.
That was tough to read, but glad you found the problem, update us when you can. On my new to me 330da I accidentally put the fresh water hose in the fuel tank once, realized it after a few seconds of pumping water. I remember putting some kind of product in the tank that helps separate out the water from the fuel, never had an issue.
Last edited:
Sorry it was so long but just wanted to explain how I got from A to Z.
Weird s#it happens with fuel issues, glad you found the problem.

Forum statistics

Latest member