Marine Fuel Tank Sending Units

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Mechanical Senders
(With optional conversion capsule.)
Reed Switch Senders Reed Array Electrical Senders Universal Electrical Senders

Materials: Cast aluminum housing; neodydium magnet (rare earth material), if using with electric capsule, wire is tinned to provide years of usage
Moving parts: Gear driven float
Signal output: Best accuracy
Expected wave cycles: Excellent
-Meets or exceeds all applicable NMMA, ABYC, and USCG standards.

Materials: 316 stainless steel; tinned wire
Moving parts: Float mechanism
Signal output: Better accuracy
Expected wave cycles: Excellent
-Meets or exceeds all applicable NMMA, ABYC, and USCG standards.
Can be used with water

Materials: Acetal composite resin; tinned or silver contact points; tinned wire
Moving parts: swing arm with contact points
Signal output: Best accuracy
Expected wave cycles: Very Good
-Meets or exceeds all applicable NMMA, ABYC, and USCG standards.

Materials: Extruded marine grade aluminum; stainless steel swingarm; thicker nichrome wire windings; tinned or silver contact points
Moving parts: Float arm
Signal output: Better accuracy
Expected wave cycles: Good
-Meets or exceeds all applicable NMMA, ABYC, and USCG standards.
About wave cycle: The fuel sender in your fuel tank is always working, even if the boat is not under power. Based on tidal changes and wave motion cycles, the float is constantly moving, whether it be by the boat bobbing in the water, taking sharp turns, or trailering the boat down the highway. This constant movement wears the fuel senders moving parts, creating an expected life cycle for the unit. The best senders are determined by what materials are used to build them, and the amount of moving parts, which together estimate the amount of wave cycles the sender will reach.

Fuel Sending Units How-To's

Replacing a Fuel Tank Sending Unit

Marine Fuel Sender Replacement

Here is a great video on how to replace a fuel sending unit.... read more

Video Transcript

All right guys, fuel gauge isn’t working. I’m suspecting the fuel sending unit but do a little bit testing here to show you. You can see how the fuel’s on Empty. Hopefully, the glare is not too much. I turn the key on, every other gauge moves. This is a Chaparral Sunesta 233, 2001 Model.

So it’s not moving at all there so what we need to do is check the sender. By doing that, here’s the fuel sending unit, just under the inspection fleet and floor. You can see it looks like a nightmare in there with rust, corrosion all over it. I’m kind of curious why it got corroded so quickly. Not really quickly but I suspect that this inspection plate here is leaking water inside there when you wash the boat or what have you, leaving water on the top there. You can see it looks like a potato chip with little pieces of rust coming off.

So what I’m going to do, I mean, obviously, I've got to replace this no matter what but I just want to make sure I don’t have a gauge problem as well. So what I’m going to do is I’m going to jump the center pin which is your fuel sending restat to the green wire which is the ground. The gauge works off of a ground system so I’ll jump those two wires and then look at the gauge. The gauge should go up with the key on, so we could get started.

All right guys, I need like four hands to do this. So just jumping the wire at the fuel sending unit. I can’t film at all at the same time but you’ll see when I’m jumping these two wires that gauge starts moving. Now confirmed. Ok, yeah. So I just went to ground and you could see how it’s going right back up there. Yup, so just jumping those two wires over.

Ok, you can see this nightmare lining up here. So all right, step-by-step, I think I’m going to pull the whole inspection cover off. I mean, there’s barely enough room to get in here on an offset. I think I’d like to seal this anyways, some 4200. So I’m going to start by popping that off.

All right, not a lick of silicone in there so obviously that’s where my water got in there probably to corrode it in the first place. Give me a little bit more room, nothing that great, I’m going to try to vacuum out before I take anything loose because obviously, I don’t want anything falling down into that junk there. Just a bunch of chunks of metal.

Yeah, I’m going to vacuum that up, trying to clean it up a little bit. Trying to start cleaning it out. I don’t have the new gas gauge sending unit yet because I don’t know what this one is. I do see an inspection cover right here. Not a cover, I’m sorry, a tag, probably giving me a little bit more details on the tank. Maybe I can find the manufacturer and get an exact match.

All right, I’m getting this vacuum turned on.

All right, I’m just spraying a little bit of Simple Green in here. Clean it up.

I did a little bit more cleaning inside here and more chunks of this fuel center just falling apart. We can almost see—I don’t know if the light is too much glare but right here on the front side it almost looks like I can see in the tank. I hope that’s not the case. All right.

Well, yeah, this is turning into a nightmare. Just tried to get one of the screws off and it really wouldn’t turn. Look at that, the whole thing is crumbling. This is going to turn into a nightmare. All right I got one out. One’s coming out but I am not going to be liking this.

Ok, I sped this part of the movie up just because it’s me frustrated trying to get this broken fuel sender out. In hindsight, I should have cut the wires that go to the fuel sender. They’re corroded anyway so I needed to clean up the connection.

It would’ve made it easier to pull out here. You can see that I’m struggling with the wire and getting it out just right. But just a little bit of patience and finesse and you’ll get it. If you got the screw out, the hard part’s over. On hindsight, don’t use the same connections.

All right, look at this nightmare. Whole thing just fell apart from the—look at this, holding it here is this, basically that. Everything else has crumbled to pieces. Unbelievable. Wow, I’m shocked I haven’t had a fuel leak. But all right, let’s see how the rest of this project goes. I’m a little nervous about it. Yeah, it’s normal. I get nervous about anything with fuel on a boat.

All right guys, I just bought this from West Marine. This is a universal Moeller fuel sending unit, 12 inches to 24 tank depth. So anyways, it’s a close—it’s actually not a close match. The other unit was a complete float assembly on an arm. This actually will ride on that metal shank that goes down at the bottom of the tank. We’ll have to cut that. So I’ve got to measure the depth of the tank and go from there.

All right guys, the instruction says to measure the depth of the tank. I’m just using a yard stick, wooden, for two reasons; I want to see how deep the tank is, and I want to see how much gas I have in there so I get an idea when I come together, I put it all in, how accurate is it to what I have on the gauge. So that’s what I’m doing. Looks like it’s a little over 16 1/2. It’s hard to tell in this hole so I’m just going to take a marker and mark it. I feel like I’m balancing.

Ok, it looks like I’ve got 10 1/4 inches of fuel according to the wet mark on the—on here, 10 1/4. And we’re about 16 and 3/4 on the tank. Ok, what I’m doing now is I’m just lining the bolts up. They say it’s an eccentric hole so you want to make sure that these fit just so.

Of course, just reach that wire hanging out is not going to help anything. Wire eventually goes into the tank but….

I’m not sure if you can see that. I think I’ve got it lined up here, this Moeller sign is facing right over this side of the tank. And seems like all the holes are lining up there. Trying to get it lined up, not drop stuff in the tank. Looks good.

All right guys, not sure if you could see this. I had to cut the arm length. Moeller’s got some real difficult instructions on how to do it, just not clear. It’s written by an Engineer, not a guy that does this kind of stuff. Anyways, the first step was finding the depth of tank and then you cut it in half, about a half an inch. So that’s what this—I had to cut this bracket.

Then the float arm length, they have a grid that tells you what length it should be and you could push on these connectors. So I’m trying to get it to fit in there right now. Just don’t drop anything in the tank. Well, see if this works. Man, getting stuck. Perfect. Man, doesn’t look like I’ll be able to get it that nice.

Well, I just manipulated it and was able to get it down in there, shockingly. You see I marked it, pre-fab, I marked the red line next to the gasket and on the tank. So hopefully this’ll line here in a second if I can wipe the mark off…which I feel like I may have. There’s the mark fo that one.

And what I’m going to do is just—I’m going to lock tight these screws but initially, just want to make sure they line up.

Ok guys, the holes are lined up. Be very careful, the new screws that come with this, they’re not the same thread pitches than ones I’ve taken out. So just make sure you’ve got the right thread pitch because if not, you can have some issue.

One thing I do like about the new screws, I don’t know if you could see it, there’s a little gasket at the back of it. You’re still going to put lock tight on it. I didn’t add any permatex seal because everything I read said not to. So anyways, those rubber seals, washers, I’m going to take them off and put them on the other one.

All right, you can see—I don’t know why but it came with two different washers. And again, I took the black—those are gaskets or rubbers—to come off the ones that came with the sending unit and put them on the old screws and I cleaned the old screws up on a bench grinder, on a wire wheel. I’m just going to use blue lock tight because everything I read said use blue lock tight.

So everything’s lined up good so I’m just give it a shot here.

All right, I put lock tight on all the screws. Now I’m just going to cross tighten them. I feel pretty comfortable with what I did.

Some dielac grease inside both sides of the connector and on the wire itself. And the reason I’m doing that now just to add a bit of protection. They guarantee they would never do this on a boat repair facility. Guaranteed.

All right, I’m just double-checking my connectors. I just put them on, they’re tight. I’ve got grease shoved in the backside of these things. I’ll shove a little bit more. You could heat shrink them if you wanted to. But it’s just a ground wire so…I don’t think it’s really necessary.

All right, we’re all buttoned up. We’ve got the screws on there. I am going to spray some CorrosionX on there after I’m sure I have no leak at all. Which I think it’s going to be pretty good. Took me a lot longer than I expected.

Almost to the moment of truth, and see if it actually….

All right, let’s see, if you remember earlier we measured the tank and it was just a hair more than half a tank. Yeah, and it’s literally showing a hair more than half a tank so pretty happy with that. Yeah, that gives you somewhat an idea.

Ok guys, good luck, I hope this helps you. Give me a thumbs up if this works for you or helps you at all.

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Testing A Sending Unit

Testing Fuel Sending Units

Here is a great video courtesy of TakePointNow on the best way to test marine fuel sending units to make sure everything is okay or to diagnose a problem you may have with your sending unit.... read more

Video Transcript

All right, so earlier what I was doing was I clamped the ground to the generator and I was touching the fuel sending unit. Trying to find out if we’re getting power so our fuel gauge works.

Well, I went in there and I probed the fuel sending unit and I couldn’t tell if the light was coming on. So I wanted to make sure that my tester worked so I needed to find something that I knew had current so I could test my ground and make sure my tool was working. So I go into the back of the alternator, touch the positive cable on the alternator, and my light lights up. So I know my ground is good. I know my tool is good.

So I go back down to the fuel sending unit and dig around, and press around, and try to get my light to come on and it doesn’t. So now I know that my fuel sending unit in the gas tank is not getting power. That could come from a couple of places; the wire is bad, the fuse that it’s hooked to in the panel is bad. But we know that we’re not getting power to the fuel sending unit.

Break it down piece by piece. Isolate the problem. And come up with the solution.

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Glastron fuel sender

How to Replace your Boat Fuel Sending Unit by Glastron (Video)

Learn how to replace your Glastron marine fuel sending unit. Presented by Frisco Boater. ... read more

Video Transcript

Happy new year, everybody! It’s the first of January, 2010. Hope everybody had a safe night out last night. I know I did because I didn’t go anywhere. Sat at home. I got two kids and a wife. Been married a long time. Just don’t go out anymore. Just kind of take it easy and watch the Dick Clark thing on TV.

Anyway, today we’re replacing that fuel sending unit that is defective. You see the old one that’s down in there, and here is my new one. You can see, there’s my fuel. It is working beautifully. So the sending unit’s fine, but however, when you go all the way down to empty, my little fuel light still does not come on, so I’m not worried about that as long as my gas gauge works.

So anyway, this is one of those Moellar or Miller, or something like that, universal ones. What I need to do is I need to get that out of there and measure the depth of the tank from the top to the bottom, and then it has, on this little universal deal. It has instructions on the back to be able to cut the right length of this rod. That way, it works properly. I’m going to get that thing out, and see what we got.

Okay, I got all the screws out. Let’s see what we got. Nice. How, and pray tell, does that come out of there? It’s a little float. Ah! There we go. Awesome. So that’s the little floaty-bob thing. Oh man, and it’s got a lot of resistance on it. When it hits right there, it catches. Interesting. Could be what’s wrong with it. Cool. I’m going to go get my tape measure. Oh nice. Looks like there’s a lot of – let me turn the light on here. Alright, you see in there, a lot of corrosion around this seal. Let’s see how bad that is. Yeah, looks like I’m going to have to scrub that off. Alright let me get my tape measure and measure the length – the depth of the tank and figure out how long to make this rod.

Alright, so what I have determined is that the tank is a seven and just over a quarter-inches deep and per the instructions, it says to use the next measurement up, which is, you can see, seven and a half inches. So that means that the arm needs to be 5-13/16’s from the sender, so I’m going to measure that from right here. I’m guessing. They don’t really say. I guess they mean the whole length of the arm from here to there. That’s what I’m going to measure off. Then it says to take and push the entire thing up to match that and then snip it off.

They said do not push these the wrong way. You push them once and once you've figured out how far you want them, stop because you can’t take them back. So let me do that. I’ll mark off this and slide it up.

Alright, so you can see my little green mark down there is 5-13/16 from there. So it said to push a little bit past it, so therefore I can slide this other retainer up just past this and leave 5/16 and then leave a little bit of play between the float and the little retainers.

Okay, so I slid it up and cut off the excess, left just a teensy bit of play around it to allow it to do that and go up and down. So now I’m going to tackle all that corrosion. I’m going to scrape it off, sand it down, make it look real good.

Alright, about 10 minutes of scraping. I used a chisel to kind of scrape the top stuff off, then I stuck my hand in there with a hundred grit sandpaper and just basically sanded it all down, trying to make sure I didn’t drop anything down inside the hole. Looks like there is some stuff down there. Some crud and some trash, but it’s probably just left over. It was there when I pulled the sender out. That’s why they make a fuel filter for, right? But anyway, I’m going to stick this back in there with its new gasket and everything like that. These things are kind of in a star pattern, so it only goes on one way. So kind of nice. No guessing. I’m going to put it in.

It wasn’t too bad. It took me a little while to get the holes exactly lined up. Seemed like every which way I tried, it wouldn’t work and I was like, “Ned, what did I do? Buy the wrong piece?” Well once you get it to line up, lines up perfectly. Screws right down, and each one of the new screws it came with had the little bit of metal at the end of the screw head, I guess to kind of help give it a good seal. It says don’t tighten it down, so I did it to 15 inch pounds of torque to make sure that it’s nice and good and sealed.

It says to pressure test it. I guess before we take it on the lake this year, I’ll take it up to the marina and have them back pressure test it to make sure it’s sealed nicely, but my dash is showing half a tank. It goes off, it goes on, and if you shake it, you see it does move, so it is reading, and that’s where I had was about a little over half a tank whenever I’d put it in storage, or started taking it to port. Hopefully that’s about what I remember correctly, but we’ll see come spring. We’ll get it in there. At least it shows me what’s going on.

As you can see, it’s not hard to replace a fuel sending unit. It takes a little bit of time, little bit of thinking to measure out everything right to get it correct, but not hard. Not hard at all.
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