Adventurer 208 gas tank volume shortage

Hi GW 208 Adventurer owners,

I think I've found a capacity problem with my gas tank and possibly you may have one with yours too. I have a 1997 Adventurer 208 with a plastic 82 gallon gas tank which only can hold about 65 gallons of gas.

I started a topic several months ago trying to find help with a an apparent gas tank problem. I went through all the advice from others and my own ideas but just couldn't figure it out. Check the post from me if you want to see all the things I tried. Then yesterday I stumbled onto something. My plastic tank is set into the boat at a stern high angle and the tank fills from the bow end. You can open your stern and bow end access ports and measure the distance from the top of the tank to the bottom of the deck very easily. My tank is set about 4.5 inches lower at the bow end where gas comes in, the pick up tube is at the stern end. So my tank overfills when there is still room at the stern. This is a significant amount of gas, I think it is about 17-18 gallons short of full making my tank capacity only (82 - 17) 65 gallons. Since the pick up tube is set a little off the bottom there is only about 60 gallons of usable gas in my 82 gallon tank. This is the reason I ran out unexpectedly.

If you own a GW 208 with a plastic tank can you please check your tank clearance at the access plate openings and let me know what you find out. Possibly mine is just an odd ball and missing something that would have leveled the tank when manufactured, but if all the 208's with plastic tanks were built like this, then you too may have a lot less gas capacity than you think.

My boat actually sits fairly level in the water. Maybe an inch or so tilted to the stern but not enough to make up for the nearly 5 inch difference. Also I usually fill the boat while on the trailer and it sits level on the trailer. Maybe there is some reason why you would want your gas tank tilted so that the fill hole is lower than the rest of the tank, but I can't think of one. It seems like the reverse, having the fill hole higher (or level) than the rest of the tank makes more sense.

Yes, you are right about a raised area where the vent and fill lines come in, but on my tank it is a very small rise, maybe and inch or two over a very small area where the lines connect. I appreciate the check, I think we have the same hull design. I heard that the poly tank was first installed in the factory during 1997, but half way through the manufacturing year. I wonder if mine was one of the first poly tank installations and had something to do with the sloping tank.

Later

This thread started a long time ago so I'm not sure anyone is following it anymore. I did find out the problem with my tank and it is confirmed by GW. My tank sits too low at the bow end. GW has never heard of this before. I will be cutting open my deck and pulling out the tank to see exactly why it sits too low. In 1997 GW went from aluminum to plastic tanks, maybe the first few went out without being leveled. At least mine did. I'm suspicious that a subfloor which levels the tank was never put in my boat. Other 208 owners, especially 1997 models should make the same measurements I did. If is possible a few 1997 208's rolled off the line and may only have about 60 gallons of use out of the 82 gallon tank. I would have never known if I didn't run out of gas last spring. GW is working with me as we figure this out and make the repair. If anyone is interested I' post photos as I open up the boat and pull the tank.

That would be about 18 gallons and the answer would be yes. I'm going offshore and need all the gas I can get. I could have really used the extra when I ran out after burning through 60 in an 82 gallon tank and almost ran up on the rocks. The main purpose of this post is to warn other 208 owners that they may have a similar problem and can do a very simple measurement to find out. Pop the access plates and measure with a tape. It could save a tow or worse.

Thanks for the help. When I take the measurements in the same places you did I get 4.5" aft and 9" forward. Mine is set 2" deeper in the bow end than yours. So yours is much better off and probably set correctly at the factory. Now that I've checked all the systems and taken measurements before and after fill-ups etc. I've got some estimates that you may find helpful for knowing just how much gas is accessible in a 208 tank. I can send all my calculations if anyone is interested but in a nutshell every inch of depth in the tank holds about 7 gallons of gas. I'm 4.5 inches deeper in the bow but 1 inch of that extra height is due to the positive slope of the deck, so I have a net difference of 3.5 inches. This represents about 25 gallons if the 3.5 inch void was constant but since it is set on a slope, there may be more like an 18-20 gallon void. When I ran out of gas and filled it at a gas station I was only able to get 60 gallons into my 82 gallon -tank so my estimate is reasonable. Since you are only 1.5 inches from level, you may only be have about a 10-12 gallon void when it is set level. If you fill at a marina and your boat slopes to the stern, you may have no void at all. Although when you add 70 you may be real close to empty. Especially since the gas pick up tube is about an inch from the bottom of the tank and account for about 6 or 7 gallons that never get used. My big lesson is don't think your tank actually can use all the gas that the tank can hold. It's probably best to only figure you will get about 70-75 out of our 82 gallon tanks. In my case 60, but I'll get mine fixed.

Hi Prince and ric,

Wow it has been awhile since I posted and I realize I never followed up since I found the problem and what I learned. I probably didn't follow up since the pain just had to end sometime. $2000 later I have the answer to the fuel tank riddle.

I discussed the problem with Grady and decided to take it to a Grady dealer to cut out the tank and see what was going on. Grady was going to help pay for some of the cost if they were at fault. We suspected that a tank support failed and the tank dropped in the bow position. Once it was opened up the problem with my plastic tank was obvious. Over time it created a 3 inch tank bulge at the stern end, right where the pick up is located. You couldn't see this through the access plate. This lifted my pick up three inches off the bottom resulting in a lot of dead storage in my tank. I did learn that the extra space at the front of the tank is per design. If you take into count that the deck angles back towards the stern, I believe that creates about a one inch difference. Also due to the way the boat sits on the trailer vs. in the water made up the other two inch or so difference. It sounds like Prince already figured that part out.

So in the end all that I needed to do was place a longer pick up into the tank which made up the 3 inch difference. The extra long pick up tube cost about $2. The cutting out my tank and replacing the deck by a pro (my model didn't have a screwed on access plate) cost about $2000. Grady didn't feel responsible for the bulging plastic tank and wouldn't help split the cost. I thought I took all the measurements I could but didn't measure the length of my pick up tube vs. the depth of the tank. A good thing for other Grady owners to check, especially if they have a plastic tank.

So I think the problem you guys are seeing since you have aluminum tanks is just how your boat sits on the trailer which is a problem I still have. I've thought about bringing ramps along to the gas station and driving my rear wheels up on them before filling up at a station or uncoupling the hitch and cranking the boat up three inches while filling. Although I've wondered what happens when I bring the boat back down after filling. Does all the extra gas come pouring out the vent? So I haven't tried that. If you have that answer let me know. I'm doing what Prince does if I go on long trips. I fill up as much as possible at the gas station, then add extra when I get to a dock so my Grady has a better angle or just fill up about 3 six gallon jugs with gas and add them to the tank once I'm at the dock.

So this is a good warning to those who fill up their boat while it is on the trailer. You aren't getting anywhere close to 82 gallons of gas in your tank. Most can only depend on 60 -70 gallons unless you have a trailer that sits your boat bow up quite a bit.

Hope this helps others from feeling the gas tank volume blues.