I've got a 1986 Hunter 28.5 with a Yanmar 2GM20F diesel. This engine uses VERY little fuel. Since I like to sail, I only use the motor to get out of, and back into, the slip plus a bit to get me into deep water. The fuel tank has a 11.5 gallon capacity. It is clear to me that I could fill this tank up once at the beginning of the season (eight months long) and never need to fill it again until the next season. Yet I have been filling the tank to the top about once a month with about a gallon of new diesel fuel (with a combo stabilizer and anti-bacterial agent added). I've been doing this thinking that it keeps condensation to a minimum. My question is this: would it be better to just use up most of the fuel in the tank during the season and either fill up the tank prior to haul out or at launch next spring? I keep thinking that I'm adding new fuel to old fuel when I should be just burning up the stuff that's already in the tank? What do others do?
Diesel Fuel Question
- Thread starter Warren M
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Keep them full
When the fuel tank is not full, the empty area is filled with air (read: humid salty air). Keep them topped-off.
When the fuel tank is not full, the empty area is filled with air (read: humid salty air). Keep them topped-off.
Two school of thought
1. Fill them in the winter to keep the water out. Problem, old fuel... 2. Fill them in the spring, fresh fuel. Problem water from condensation. I pick 2.... I want fresh fuel!
1. Fill them in the winter to keep the water out. Problem, old fuel... 2. Fill them in the spring, fresh fuel. Problem water from condensation. I pick 2.... I want fresh fuel!
Never had problems with old diesel.
I personally would go for the full tank method too. If you are only using 6-8 gal./yr. then your option is going to be dispose of the old diesel before then new season. Of course you are probably going to have a tank that is full of algae and water when you go to pump it out. I have gone from season to season without worrying about fresh diesel. Now Gasoline, that is a different story. This is where a fuel stabilizer is a real must. I have had this problem with my lawn mower and outboard engine.
I personally would go for the full tank method too. If you are only using 6-8 gal./yr. then your option is going to be dispose of the old diesel before then new season. Of course you are probably going to have a tank that is full of algae and water when you go to pump it out. I have gone from season to season without worrying about fresh diesel. Now Gasoline, that is a different story. This is where a fuel stabilizer is a real must. I have had this problem with my lawn mower and outboard engine.
Keep the tank pressed up!
Warren, I've got a 2GM20F in my C&C 26. I don't use much diesel from one year to the next. Most of the diesel in my tank is 1 or 2 years old with a bit of new that I used to top up last winter before I laid her up. I put in a dash of conditioner also! She started first time this spring & I've never had any trouble. I'd be more concerned with condensation in the tank. But then your primary filter should show this up pretty quickly if it's present. sam
Warren, I've got a 2GM20F in my C&C 26. I don't use much diesel from one year to the next. Most of the diesel in my tank is 1 or 2 years old with a bit of new that I used to top up last winter before I laid her up. I put in a dash of conditioner also! She started first time this spring & I've never had any trouble. I'd be more concerned with condensation in the tank. But then your primary filter should show this up pretty quickly if it's present. sam
Bi-O-Bor etc.
Be carefull about adding anti-microbials to small amounts of fuel. Too much is toom much. Once a season should be enough (proper measurement).
Be carefull about adding anti-microbials to small amounts of fuel. Too much is toom much. Once a season should be enough (proper measurement).
One more opinion
1, keep the tank full to prevent condesation. Water is diesels worst enemy. 2, use anti bacterial only once a year, fall when you put it up for storage is best. 3, Check the bottom of the fuel tank for water and pump it out in the spring. 4, make sure you have a water seporator filter in the fuel line, and replace it each spring. 5, You can use a product like stabil to keep the fuel freasher, but it's not nessasary with diesel.
1, keep the tank full to prevent condesation. Water is diesels worst enemy. 2, use anti bacterial only once a year, fall when you put it up for storage is best. 3, Check the bottom of the fuel tank for water and pump it out in the spring. 4, make sure you have a water seporator filter in the fuel line, and replace it each spring. 5, You can use a product like stabil to keep the fuel freasher, but it's not nessasary with diesel.
I want fresher fuel
For the last year my fuel tank has never been full. It is a 20 gallon tank and the PO said not to fill the tank. So far so good. I check the water separator and there has never been any visable water. In some parts of the country there might be a lot of air exchange via the vent but I doubt that there is much. The air in the tank is basically dead air that doesn't exchange with the outside air very much. Air volume changes proportionate to the absolute temperature change. So if the temperature drops 20 degrees overnight a big drop here from 35 to 25 it would be 273+25/273+35=0.96 times 10 gallons (1/2 tank) = 9.6 gallons for a gas exchange of 0.4 gallon. And even saturated air doesn't have that much water. Now if you have a huge tank you might generate a lot of condensation. You also have to figure that the water will moderate any temperature changes and that some of the water will evaporate during the heat of the day.
For the last year my fuel tank has never been full. It is a 20 gallon tank and the PO said not to fill the tank. So far so good. I check the water separator and there has never been any visable water. In some parts of the country there might be a lot of air exchange via the vent but I doubt that there is much. The air in the tank is basically dead air that doesn't exchange with the outside air very much. Air volume changes proportionate to the absolute temperature change. So if the temperature drops 20 degrees overnight a big drop here from 35 to 25 it would be 273+25/273+35=0.96 times 10 gallons (1/2 tank) = 9.6 gallons for a gas exchange of 0.4 gallon. And even saturated air doesn't have that much water. Now if you have a huge tank you might generate a lot of condensation. You also have to figure that the water will moderate any temperature changes and that some of the water will evaporate during the heat of the day.
Top up at the end of the season
Warren, I have had my CS 27 with a 12 US gallon tank for 3 years and I use about a quarter of a tank per season. I have been filling it once at the end of the season before haulout and storage. So far the diesel starts fine and there has never been any water in the primary filter bowl. The boat is in fresh water on the Great Lakes. Kevin
Warren, I have had my CS 27 with a 12 US gallon tank for 3 years and I use about a quarter of a tank per season. I have been filling it once at the end of the season before haulout and storage. So far the diesel starts fine and there has never been any water in the primary filter bowl. The boat is in fresh water on the Great Lakes. Kevin
Fill it and treat it
What I do now is fill the tank when the weather starts getting cold (I sail year round) and give it a treatment of stabilizer and anti-bacterial agent. Then I'll treat it every time I add fuel. (5 gallons every 6 months). One year I didn't didn't do this and the next year I had an expensive repair bill because of all the bugs that grew in the fuel tank. When I drained the fuel tank it had 10 gallons of diesel fuel in it, 5 of which I had added a month earlier and it was as black as coal! Don't do this to your engine!
What I do now is fill the tank when the weather starts getting cold (I sail year round) and give it a treatment of stabilizer and anti-bacterial agent. Then I'll treat it every time I add fuel. (5 gallons every 6 months). One year I didn't didn't do this and the next year I had an expensive repair bill because of all the bugs that grew in the fuel tank. When I drained the fuel tank it had 10 gallons of diesel fuel in it, 5 of which I had added a month earlier and it was as black as coal! Don't do this to your engine!
Here is a link about condensation in tanks
http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm Now this reminds me that the O ring on my fuel filler cap is gone!!!
http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm Now this reminds me that the O ring on my fuel filler cap is gone!!!
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