Fuel Consumption - Mercruiser I/O 5.7L 260hp

I own an '85 Chris Craft Scorpion with a '85 Mercruiser I/O 5.7L 260hp (350 Chevy) pushing her across the lake. Everything is stock - one previous owner who was a marine mechanic so well taken care of - clean engine - no noticeable leaks. The gas gauge seems a bit odd at times where it stays on full for the first 3-4 times I take her out on the water then when the gauge starts to decrease it rapidily drops. Since it appears as though the gauge might be a bit off, whenever it gets close to 1/4 of a tank, I fill her up.

So far we have had to fill the fuel tank up twice - approximately 35-40 gallons of fuel when gauge is at 1/4 tank mark - and this last time I filled it up I decided to keep track of the engine hours. It appears as though after 5 engine hours I am burning 35-40 gallons of fuel and wanted to know if this seems normal or excessive. This also isn't 5 hours of full throttle operating. Usually have the boat around 2500-2800 rpms when cruising on the lake but I would say it is an average of around 2000 rpms while running the boat.

Thank you for your feedback.

Re: Fuel Consumption - Mercruiser I/O 5.7L 260hp

How big is the boat?? You are running at around 7-8 gallons per hour. Depending on how heavy you are with your right hand that doesn't sound too bad. Now, running at 2000rpms, you aren't on plane, no way! You may find you are more efficient around 2800-3000rpms where the boat is on plane comfortably. There are a lot of variables here, pitch of your propeller, weight of your boat, how much weight has been added (passengers, stuff, etc...) etc....etc.... If you were running at full throttle, you could expect at least 40 gallons per hour.

Re: Fuel Consumption - Mercruiser I/O 5.7L 260hp

can compare to AQ260 (same engine) on this chart for a rough idea
http://freespace.virgin.net/simon.sherlock/Volvo_fc.htm

Re: Fuel Consumption - Mercruiser I/O 5.7L 260hp

My boat's LOA is 25'5', weighs 4500lbs dry, hold 60 gals of fuel and has the 5.7 EFI 260HP motor with a Bravo III drive, 24 pitch SS props. I usually have 4 people on it when out and I get around the same, 7-8 gals an hour. I run my boat anywhere from 3200 to 3500 rpm, depending on water and if I am using tabs or not. If the water is great I am running around 35 mph @ 3500RPMs.

Every boat is different but it sounds like yours is running about the same as mine... but at a much lower rpm/speed. I would try to run it in the 3000-3500 rpm range and see how much you burn. I was always told that is the most fuel efficient range for my engine.

Re: Fuel Consumption - Mercruiser I/O 5.7L 260hp

Thanks for all the feedback. The boat is 21' and weighs around 3500lbs. Based on the feedback it appears as though she is running like she should that the fuel she is using is normal. Now if I could only get the wife to quit complaining about how much it cost to fill 'er up

Re: Fuel Consumption - Mercruiser I/O 5.7L 260hp

Fill it up without her there!!! My wife also complains a bit when I fill ours up. But she has a big smile on her face when we are out cruising around.

Re: Fuel Consumption - Mercruiser I/O 5.7L 260hp

Great advice!