Gas Tank Capacity Problem

[tomolalla]

Hello Out There,

I own a 1997 20' Adventurer with a 82 gallon plastic gas tank. For the first time ever, I ran out of gas. It was very embarrassing (and slightly dangerous) since I thought I had 20+ gallon to spare. I usually make sure I have plenty and watch my running time since my gas gauge is undependable. I eventually received 10 gallons of gas from a buddy and made my way to the dock, then immediately to a gas station. To my surprise I could only top my tank off with 58 gallons. If I include the 5 or so left from my 10 gallon emergency supply leaves my tank with about a 62 gallon working capacity. I've checked my vent which seems fine and eventually was able to add another 6 or so gallons at home by slowly pouring in more gas while the boat was at a slightly different attitude (bow up). Now at 68 gallons I'm totally toped off.

Have other owners noticed this capacity shortage or is this just something I should expect? By expect, I mean, does the tank only has a 70 gallon working capacity with 12 gallons of dead storage. The dead storage being what resides in the tank below the gas uptake hose. Any other ideas what may be limiting my capacity?

This is becoming more important to me since I'd like to make some longer off shore (WA State) journeys to find albacore tuna and will need every drop.

 

[Pez Vela]

The original factory installed aluminum FMT's in my Grady held the advertised capacity ... EXACTLY. I think you need to measure the depth of the tank and compare it to the length of the pickup tube.

 

[ElyseM]

the manual for your boat/year indicates an aluminum tank. if your's is poly, it was probably replaced. may not be 82 gals. also, pickup may not be down as far as it should. are you original owner?

ron

 

[tomolalla]

Yep, I thought I had a smaller replacement tank for awhile but found out that 1997 was the year Grady started to switch over to a poly tank. So there are both poly and aluminum tanks on the 1997 series. I had that fact verified by GW and it is the original equipment. I also found a sticker on the tank saying 82 gallons. So it may just be a short pick up tube. I'll see if I can figure out a way to measure it. I wonder if anyone else out there with a poly tank has noticed this problem? Thanks for the replies.

 

[seasick]

You should have more capacity than you appear to have. Do you have a fuel gauge and if so, did you notice the readings when you ran dry?
There could be several reasons for your situation. The tank was angled front side down. If you have digital gauges, you can sort of check the tank by moving weight fore and aft while watching the gauge. With a half full tank, moving two people from the helm to the stern should make the gauge if digital move one or two bars.
Your digital gauge should also have been flashing if there were 20 gallons or less of fuel (assuming the tank has the correct sender)

Your pickup tube may be short or broken r have a hole in it. That is tough to check.

A third and very low probability cause is a loss of fuel flow and prime. There are things that can cause loss of prime but I doubt that is your problem

 

[lodgecreekgrady]

To measure the pickup tube you need to first run some of the gas out. You don't want it completely full. Take the pickup tube out of the tank and measure it and inspect it to be sure there are no holes in the side of it. Get something small and long enough to reach the bottom. A 1/4 or 5/16th wooden dowel rod should slide in the tank where the pickup tube goes. Shove it to the bottom and mark where the top of the tank is. Take it out and measure it. Compare the measurement of the dowel to the measurement of the pickup tube from the bottom to the threads where it screws into the tank. if the pickup tube is alot shorter than the mesurement of the dowel then you are not using all the fuel in the tank. If you need to replace it be sure not to make it too long that it hits the bottom of the tank and causes a restriction. The pickup tube should be off the bottom of the tank around 1/2 inch or so. If you want it closer cut the end at a slight angle so you know if it is too close to the bottom you won't restrict the flow. You may want to research to see how close you can go to the bottom but I like it around 1/2 inch in case you get some water in the tank it won't pick it up as bad.

 

[tomolalla]

I'll try measuring the pick up tube this weekend and let you know the results. I'm wondering if since I have a poly tank that can flex if they were extra conservative with the length of the pick up tube. In other words the tube is extra short so it wouldn't hit the bottom and create a block as you mention. Were those measurements (1/2 " from bottom) off of an aluminum tank? Thanks for the ideas everyone. Keep them coming if you have any more.

 

[lodgecreekgrady]

Yes that was aluminum tank. You may have a plastic pickup tube. I am not sure but in any case you want to be sure it is close to the bottom but not on it. It could be that it is a plastic pick up tube in a poly tank and it may be cracked or lost its shape and curled up off the bottom some. when you take it out you should be able to tell. I wouldn't think that a poly tank would flex all that much. 1/2 inch should be fine but that is just my opinion. There may be a standard but i think 1/2 is in the ball park. Good luck.

 

[tomolalla]

It's been a long time since I last posted so I'm not sure anyone is still following this thread, but I have made some progress towards solving this case of the missing gas.

I took a lot of advice from the forum helpers and eventually got around to checking my intake tube. It is plastic, in good shape and comes to within an inch of the bottom of the tank. While doing this I measured the level of gas in my 82 gallon tank. The tank is 12 inches deep (inside dimension) and my gas level was 6 inches deep. Assuming a consistent ratio of 12"/82 gallons this means ever inch in my tank accounts for very close to 7 gallons. So I had 1/2 tank of gas (about 41 gallons) and went to fill it. The boat stopped taking gas at 24 gallons, further filling resulted in over topping. So I was about 17 gallons short of being full. Just to make sure I didn't screw something up I re-measured the gas in my tank with a dowel. I had 2.5 inches of unfilled space in my tank (about 17 gallons). So the numbers add up, just not getting a full tank when I fill up.

Since I believe there is pretty simple system (inlet, outlet, vent) I'm now trying to figure out a venting problem. If anyone out there has had venting problems and simple ways to figure it out, I'd appreciate some advice before I start taking stuff apart.

I've noticed something I cant explain and may be a clue: When my tank overfilled slightly at the pump and gas was around the outside of my cap I noticed a yellow residue. The next time I filled the residue wasn't there, but it did show up one more time after that.

Thanks for reading this..sort of long winded but driving me crazy and I need a full tank to chase the albacore that are now off the Washington Coast.

 

[seasick]

It might help to know what your fuel gauge displayed before the trip and after you ran out of fuel.
I don't know what the yellow stuff was but since you over filled, it could be anything that was caked around the filler fitting or in it at the top.
If you think you ran out of fuel due to a venting blockage, the solution at that time would have been to unscrew the filler and see if that helped.
As mentioned, it is very difficult to judge the actual amount of fuel in that vessel since small changes in the angle of it can affect the reading. On my 208, going from on plane, trimmed down, with three boaters to plowing up to planing can change the gauge reading by two bars. That represents almost a 20 gallon difference in fuel but we know that in those instances, the amount of fuel hasn't changed

 

[tomolalla]

My thread is getting pretty long so you may not have worked your way through it. In a nut shell my problem is that I cannot fill the tank before it overflows. I've actually measured levels with a dowel and I'm not depending on my gauge. I end up about 17 gallons short of 82. I've checked everything and thought the vent was OK. I have blown through the vent hose from the tank end and it didn't seem plugged. Although a problem with the vent is the only thing that makes sense now so I will pull it apart. Maybe some of that yellow gunk is plugging my vent which is in the filler hole itself. I do not have a separate vent independent of the fill hole. Later.

 

[seasick]

My thread is getting pretty long so you may not have worked your way through it. In a nut shell my problem is that I cannot fill the tank before it overflows. I've actually measured levels with a dowel and I'm not depending on my gauge. I end up about 17 gallons short of 82. I've checked everything and thought the vent was OK. I have blown through the vent hose from the tank end and it didn't seem plugged. Although a problem with the vent is the only thing that makes sense now so I will pull it apart. Maybe some of that yellow gunk is plugging my vent which is in the filler hole itself. I do not have a separate vent independent of the fill hole. Later.

If the vent were blocked, you would still be able to add gas, just at a much slower rate. If the gas actually is visible in the fill then the tank is full.
I am not sure how you determined that your tank took 17 gallons less than spec. You would have to be certain that it was completely empty and that may not be the case.
For example, if the filler were 1/2 above the bottom, the tank is symetrical, it is perfectly level and is 12 inches deep, there would be 4 gallons in the tank when the pickup ran dry. If the tank were slightly tilted forward, there would be more. Of course, when at sea, the tank is usually tilted back which moves more gas towards the pickup but as soon as you come off plane, the fuel shifts forward and if the level is low, the pickup can suck air and the motor will loose prime.
Ypu also have not told us what the guage displayed before and after filling. Not that if you have one bar displaying ( for example when two bars changes to one), you could have close to 30 gallons in the tank. When the one solid bar starts flashing, you can have 20 gallons left.

 

[tomolalla]

Hi Seasick,

I guess my writing skills are going down hill. I thought I explained how I came up with the 17 gallon shortage in my message from a couple days ago. I am not depending on my gauge, I have taken that out of the equation and have made direct depth measurements in my tank by removing the tank sensor and using a dowel and a ruler. These measurements were made before and after I went to the gas station, no boating in-between. My tank overtopped at the gas station but when measured after I got back home it still was short by 17 gallons. I have used a level to be sure the boat is at the same angle during filling and when being checked at home for level in the tank.

The tank definitely overtops without being full. Possibly if I were to wait 5-10 minutes maybe I could get some more fuel in the tank but that isn't very efficient at a busy fuel dock and not the way the system is supposed to work.

Unless I hear back from someone who has helpful advice in taking apart the vent system, I'll give it a shot myself. Of course all the parts that need to be removed are tucked up into some tight spaces under the rail.

 

[enfish]

Assuming you're filling while on the trailer? How does your boat sit when connected to your tow vehicle? Since you're manually measuring the fuel level through the sending unit hole (I think?) at the aft end of the tank, and the fill tube is at the front of the tank, if the front of the tank is slightly lower than the rear, the pump will shut off before the tank is completely full. I'd try jacking the tongue of the trailer way up to see if you can add more fuel. The only way your estimate of 17 gallons short is accurate is if your fuel tank is perfectly level. For reference, I have the factory poly tank in our 208 (hull was replaced under warranty in 1997, and the poly tank was one of the free upgrades we got because of it), and if I tried to remove the sending unit from the tank when it was completely full while on the trailer, I'd have fuel pouring out the top of the tank since the boat sits slightly bow high when in the trailer.

 

[tomolalla]

Yes, good thinking and something I took into consideration. I've set the level on my boat while on the trailer at the gas station and at home. The boat is level and on the trailer at both locations when I did my dowel testing.

 

[seasick]

Yes, good thinking and something I took into consideration. I've set the level on my boat while on the trailer at the gas station and at home. The boat is level and on the trailer at both locations when I did my dowel testing.

If I loosen the sender with the tank relatively full and the boat in the water ( and I have done so) gas will pour out of the tank. I can't see how using a dowel to measure the depth of the gas at that one spot can be an accurate measure of volume. Assuming the tank was level fore to aft, it could be slightly tilted port to starboard. In addition, I am not certain that the tank is a true rectangle. My guess is that when you filled it, it was probably pretty full.
I also can't say with certainty that the tank itself is level when the deck is level. The tank may be inclined.
If you want to fill the tank for sure, tilt the stern up, bow down

 

[enfish]

If you want to fill the tank for sure, tilt the stern up, bow down

Should be the other way around, no? Stern down, bow up since the fill tube and vent are at the bow end of the tank.

 

[seasick]

If you want to fill the tank for sure, tilt the stern up, bow down

Should be the other way around, no? Stern down, bow up since the fill tube and vent are at the bow end of the tank.

The reality is that the fill and vent tube are much higher than the tank's upper surface. I think you are correct that there is a better chance of the tank being full with the bow up but assuming that an air pocket doesn't form in the rear of the tank, bow down should work too.
What the heck was I thinking?

 

[tomolalla]

Hello out there,

I've been listening to your advice and did some more checking today and I may have found something I didn't notice before. I made some measurements and think I may have found something. When I measure the stern end of the tank near the sender unit, it is 3.75 inches from the top of the tank to the bottom of the deck. The same measurement at the bow end, near the vent and fill hose is 8.25 inches. The plans I was sent by GW make it appear that the tank is uniform shape throughout. So if that is true, the bow end of the tank is 4.5 inches lower than the stern. Shouldn't this tank be even with the deck fore and aft? Since the bow end is lower I would think you could never fill the tank unless the bow is cranked up at least 4.5 inches higher than the stern. Are tanks put in at this much angle towards the bow or did I discover a factory error?

 

[seasick]

Hello out there,

I've been listening to your advice and did some more checking today and I may have found something I didn't notice before. I made some measurements and think I may have found something. When I measure the stern end of the tank near the sender unit, it is 3.75 inches from the top of the tank to the bottom of the deck. The same measurement at the bow end, near the vent and fill hose is 8.25 inches. The plans I was sent by GW make it appear that the tank is uniform shape throughout. So if that is true, the bow end of the tank is 4.5 inches lower than the stern. Shouldn't this tank be even with the deck fore and aft? Since the bow end is lower I would think you could never fill the tank unless the bow is cranked up at least 4.5 inches higher than the stern. Are tanks put in at this much angle towards the bow or did I discover a factory error?

Now that you mention it, when I look into the aft inspection port, the tank is farther away than when I look into the mid-deck access hole.
The tank is slanted so that fuel pools in the rear near the pickup when the tank is less full. That way, you have a better chance of using most of the gas even with the deck level and the bow trimmed down.