Keeping the Tanks Full?

When my car gets to 1/2 a tank, I top it off.

When I had airplanes, I topped the fuel tanks off before putting the plane to bed. It helped prevent condensation i.e., water collecting in the fuel tanks.

Back in the days when I had gasoline powered boats, I put the boat to sleep with 1/2 tanks unless I knew I was going on an extended cruise in which case the tanks would get topped off.

Now I have this beautiful boat with Cummins diesel engines and have been studying about diesels for several days now. Water in the fuel is a big deal. Here in South Florida, especially during the "winter" the sun can heat the boat up during the day and as soon as the sun sets, the temperatures drop setting up a recipe for condensation. My game plan is to top off the fuel tanks after each outing in order to help prevent condensation from forming. I was wondering how many of you do the same thing or if you have a different method, I would be grateful if you shared it with me. Full tanks means about another 3,200 pounds added on to the gross weight of the boat. The big cummins engines don't seem to notice the extra weight as the boat gets right up on plane. In the world of jet airplanes, the engines burn 10% more fuel to carry the extra weight. In other words you pay a penalty to carry extra fuel. I'm more concerned with clean fuel that burning a little extra fuel. Your thoughts?

Just as a side note, flight planning a jet means enough fuel to get to your destination considering winds and weather. Additional fuel to get to the furtherest alternate airport and enough fuel to hold for 45 minutes (Domestic flights). Airlines tightly regulate the amount of fuel carried because of the 10% burn penalty. And if you didn't know it, flight planning fuel is done by 1000's of pounds and not gallons.

Congrats on the boat!! She's a beauty and you're going to love her!

There's no need to top off each trip, unless of course they're some really long trips. I generally don't fill up until each tank is at or below 1/4 tank. And I don't fill up for the winter. Not a lot of science there, just less weight is better fuel efficiency.

You'll find lots of opinions on the condensation issue, but mostly just opinion. Bottom line is that the math and science of it is clear there's not enough volume of air to produce significant amounts of water via condensation. Also gasoline and diesel are very different with respect to water. Diesel absorbs water more readily which creates new issues. And you're more likely to get water in the fuel via the fuel dock than condensation anyway.

My view is simply to use Frank's diesel management plan and use the fuel I've got. Full tanks mean less agitation and higher possibility of growth. Again, not particularly scientific but a plan. Find the plan that works best for you and use it.

It is the air space above the fuel in the tanks that cause condensation problems. I large air space allows ambient air to fill the area above the fuel then, as the temperature cools and re-warms moisture condenses on the interior tank walls........the more air space you leave in the tanks, the more moisture collects on the tanks walls above the fuel.

In the spring, summer and. fall, I don't much worry about it because in NW Fla there isn't a lot of temperature differential between night and daytime. Come October to April, I never leave the boat with the tanks less than 3/4 full, and if I will be away from the boat for a week or more, I fill the tanks and treat the fuel I add before leaving the boat.

45Gunner - read FrankW's post about diesel fuel additives and treatment...

http://www.clubsearay.com/index.php?threads/diesel-fuel-management.84670/

I do not top off after every trip as a conscious activity.

Summer time I keep the tanks at 3/4 or above. This is driven by Hurricane planning. We don't run the boat as much during the summer, but I always want fuel onboard in case I have to move the boat due to storm situations.

Rest of the year, we are running the boat usually at least every 4 weeks. We keep the boat in Clearwater, but over the past year I have bought the majority of our fuel down the coast to the south. I want enough fuel on board when we get to the boat that I am comfortable running 100+ miles before I get fuel.

Net, most of the time year around when we leave the boat it has at least 3/4, almost never full.

Carter, the link you provided to Frank's info on diesel fuel management didn't work for me. Any other suggestions?

Gofirstclass said:

Carter, the link you provided to Frank's info on diesel fuel management didn't work for me. Any other suggestions?

Click to expand...

You have to be a sponsor to get access

Good advice to read the diesel fuel management post. Good info about the care and feeding of diesel fuel including various fuel treatments. I became a sponsor just to get that and it was worth it.

For storage definitely keep the tanks full. The less opportunity for water in the tanks the better. I would also keep them full at times of the year when there is going to be a lot of temperature differential between day and night. The rest of the year - in season - I guess its your call. This year (first season with the boat) it was between 1/2 and full. I generally like to have enough fuel on board so we can take a hop across or down the LI Sound without having to be concerned about fuel.

Gofirstclass said:

Carter, the link you provided to Frank's info on diesel fuel management didn't work for me. Any other suggestions?

Click to expand...

I’m sorry GFC - I didn’t even think about it being a Club Level thread.

45Gunner won’t be able to see it either...

I just fixed that.. I'll check back in a day or two to see if it's been processed.

Processing took about 2 seconds, not 2 days. I'm now Gold again and able to link to Frank's info.

Thanks. I didn't realize my membership had lapsed.

Gofirstclass said:

I just fixed that.. I'll check back in a day or two to see if it's been processed.

Click to expand...

You're in now... Happened to me a few times ...I didn't know My sponsorship expired

IMHO...water from condensation in the tanks is a minor consideration compared to other sources as previously mentioned like pumped in from a fuel dock. Another source can be leaky fuel cap o-ring. Seriously, when was the last time you inspected them or replaced Them? Are they on your PM list?

Besides being the main ingredient to the growth of “slime”, water is also bad considering the fuel tanks are metal, and fuel tank corrosion is a major issue (it pops up on here occasionally). Pin holes at the bottom where water has accumulated for years will do this eventually.

I usually only fill the boat 1-2 times a season here on the lake. I know when the gauge hits a certain level, I need to add 200/100 per side and adding the right amount of “Franks Cocktail” is easy to measure and there is some agitation as fuel is added. As I get to the bottom 1/3 if there is any crud in the tank it usually starts to show up in the Racor.

Power Services Diesel Kleen product line has a couple different formulations that I employ at different times depending on what’s going on. The grey bottle is the standard injector cleaner/cetane boost/ lubricity formulation. The white bottle is the winter formula that adds an anti gel and water remover. The green Clear Diesel is a tank cleaner that removes water and slime.