Fuel reading way off

[digthemup]

I went to take my 2002 Cobra DC201 out of the water, and the tank showed 1/4 tank, which I though it odd for the amount of use. I did not pay attention when I put in exactly 25 gals. of fuel with a bottle of Mercury decarbonization fluid where the gauge moved up to. Motor died within 100 yards of dock after starting fine, and I got it back to the dock with my TM within a few minutes I figured it was out of fuel since my primer bulb was way soft. Motor started right up after I dumped 5 gal of fuel, but now I need to figure this issue.

Is the sending unit bad?? or is the gauge bad?? anyone experience same situation I would appreciate any good intel.
Thank you to everyone in advance.

[Ryno 615]

I cannot trust the fuel gauge in my boat. You can ohm out the gauge to see if it within spec, just need to know what the tolerances are for your gauge. I've changed the sending unit in my boat, and did not seem to help my readings. Next time, I am going to change to a different style sending unit, to get away from the float arm type.

[digthemup]

I cannot trust the fuel gauge in my boat. You can ohm out the gauge to see if it within spec, just need to know what the tolerances are for your gauge. I've changed the sending unit in my boat, and did not seem to help my readings. Next time, I am going to change to a different style sending unit, to get away from the float arm type.

Ryno,
That is a great idea of getting an Ohms reading, however, I have no idea what the specs would be or where to get them. Hopefully, somebody may have or know where to get it, so I can figure out which one to replace and where to buy it.

[digthemup]

Ok, depending on the type of fuel sender the tank has the Ohms reading can be 200-250 empty to 30-50 full, so I will need to take the driver seat out and get to the sender.
Does anyone know if it is a slider or an arm sender? that would be of great help.
Thank you

[Ryno 615]

Mine had an arm. My next sending unit will be a reed style, to see if it is more accurate.

[digthemup]

Mine had an arm. My next sending unit will be a reed style, to see if it is more accurate.

Ryno,
Are you saying that the unit you found was an arm style electrical single center wire with ground on the head? which works by reading resistance.
Moeller makes a Universal Reed Array Sending Unit – Adjustable 6-24″ arm, part #035791-10, which I believe it should work if the perimeter specs are compatible with the gauge.

[Steve from Dallas]

This is what I found odd about mine. I replaced the pickup tube a couple of weeks ago. The pickup tube is about 12" long and sits in the middle of the tank which makes complete sense. While I was there I thought I would remove the fuel sending unit as well to look things over. I was able to move the arm up and down and was getting correct readings on the gauge. The odd part is the fuel sending arm is less than 6" long and is mounted behind the driver. I know I am not getting accurate readings based on how much I fill versus what the gauge shows. I can't for the life of me figure out the shape of the tank where this configuration would work.

[digthemup]

This is what I found odd about mine. I replaced the pickup tube a couple of weeks ago. The pickup tube is about 12" long and sits in the middle of the tank which makes complete sense. While I was there I thought I would remove the fuel sending unit as well to look things over. I was able to move the arm up and down and was getting correct readings on the gauge. The odd part is the fuel sending arm is less than 6" long and is mounted behind the driver. I know I am not getting accurate readings based on how much I fill versus what the gauge shows. I can't for the life of me figure out the shape of the tank where this configuration would work.

Steve,
By chance, did you measure the depth of the tank? It makes sense that if the sending unit is under the driver seat, and the tank is much deeper in the middle, I should have had fuel left while the sensor would have read empty, which I would have been very good with it.
Right now, the sensor read 1/4 tank while the tank was completely empty. Praise God, that my friend had 5 gal in his shed of non ethanol fuel when I used my TM to get back to the dock, so I was able to get her running putting my mind at rest.

[Ryno 615]

This is the style of sending unit that was/is in my boat
When I decide to replace it again I will go with this style
I have a 44 gallon INCA tank in my boat (99 model 201d). Some years of the cobra's may have a Moeller tank. If I remember correctly, the 44 gallon was an "upgrade" from the factory, so some boats may only have a 30 or so gallon tank. My tank seems to be the same depth from one side to the other, but I've seen some pictures of tanks being a U shape, here mine is square. Also, my tank was 11" deep I do believe.

This pic is from when I was having what I thought was a gas tank issue. And yes, I cut out the entire section thinking my tank had a hole in it. Honestly needed to be done, there's no reason these tanks should've been built into the boat the way they were.

[Steve from Dallas]

I should have clarified. The fuel tank sending unit and the pickup tube are on the same plane. The pickup tube goes down 12". When I took the fuel sending unit out I was going to check the depth with the pickup tube. It would only go down a couple of inches before it hit. The sending unit had to be turned so it went in sideways to bypass whatever was below it. I have the 34 gal tank on 1998 188D. The tank seems to be shaped like a "L" where the top of the "L" is where the pickup tube and the sending unit sit. The lower part runs under the seat.

[digthemup]

As far as I can recall, I have the larger tank, but I will look at the original order sheet which should have it on there. IMHO, with the crap fuel we have these days, the smaller tank would be of a benefit so fuel would stay fresher by emptying out the tank more frequently.
I use the Don Weed proscribed cocktail additive in the 3.0L forum, which seems to help alot.