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Fill the tank or run with half?
WhalerYo	#1  Posted on 06/26/07 - 2:51 PM
Member Posts: 17 Comments: 0 Joined: 05/08/06	I fill the 125 gal tank of my 23 Conquest I/O whenever I gas up. Now I'm wondering if this is the right way to go performance/mileage-wise. I usually only need to fill up three times a season and I'm wondering how much mileage improvement I'd see if I only filled it around half way each time? I average 2.65 mpg and fill up when my GPS tripometer shows around 260 miles. My small sample of data (9 entries) doesn't seem to show any improvement in mileage when I go longer before filling up, but common sense tells me that the extra 500 lbs or so of fuel should have an impact on mileage. Does anyone have numbers from a fuel-flow meter that quantifies the relationship between fuel load and mileage? Bill
joninnj	#2  Posted on 06/26/07 - 3:42 PM
Member Personal Page Posts: 408 Comments: 3 Joined: 06/07/07	Hi WhalerYo I agree with your logic, but I probably would be more concerned about condensation build up in the tanks. This is prone to happen when using ethanol, (which most of use now). This happens when tanks are not full, allows condensation… Good luck Jon
DelawareDan	#3  Posted on 06/26/07 - 6:10 PM
Member Personal Page Posts: 328 Comments: 2 Joined: 05/24/07	good question and a good answer! I'll be checking this thread as others weigh in. The common logic is to fill the tank (and additive) before decommisioning for the season. But if you've got to put 300 miles on her to burn off that fuel in the Spring, you might be burning some pretty old gas. And the alcohol seems to store even more poorly than "real" gas.
joninnj	#4  Posted on 06/26/07 - 6:19 PM
Member Personal Page Posts: 408 Comments: 3 Joined: 06/07/07	Since I started using ethanol, I now empty my tank completely for the season. Odd right? Try to keep full during use, empty during off season. I had to siphon out about 15 gallons in to the Jeep last year, little bit of a pain to line up the SUV and boat Jon
joninnj	#5  Posted on 06/26/07 - 6:21 PM
Member Personal Page Posts: 408 Comments: 3 Joined: 06/07/07	Since I started using ethanol, I now empty my tank completely before the season. Odd right? Try to keep full during use, empty during off season. I had to siphon out about 15 gallons in to the Jeep last year, little bit of a pain to line up the SUV and boat Jon Edited by joninnj on 06/26/07 - 6:31 PM
WhalerYo	#6  Posted on 06/27/07 - 11:21 AM
Member Posts: 17 Comments: 0 Joined: 05/08/06	Interesting - I've heard the opposite regarding Ethanol, that with aluminum tanks, you should store over the Winter with the tank nearly full (with fuel stabilizer added). That's the way I've done it for the last 3 Winters. A boater in my marina said that he fills his Formula 34PC tanks only half full because Ethanol gasoline loses octane fairly quickly. He also puts in an additive with every other refueling. If the concept of losing octane is valid, that might explain why I don't seem to get better mileage as the tank empties. Lighter weight + lower octane = same mpg?
joninnj	#7  Posted on 06/27/07 - 12:56 PM
Member Personal Page Posts: 408 Comments: 3 Joined: 06/07/07	Here is good article on Ethanol. http://www.boatus.com/news/e10_0706.htm Jon