Accuracy of fuel tank gauges

[Jack]

My 2000 340 fuel tank gauge is way off. It shows a little more than 1/4 tank full, BUT, only needed 9 galllons to fill it. If the reading was accurate it should have had only 7-8 gallons in it, leaving at least 20 to fill. I guess it's off to my favor, so I should not run out but this is not a good thing.
Anyone else have this problem and how do I fix this?

 

[Rich Stidger]

T/S to find the problem

It sounds like you may have a problem with the gauge system.

Does it show full when the tank is actually full?

You should check the following:

1. Connections between the sender and the display gauge
2. Test the gauge display.
3. Test the sender itself.

If you are lucky, the problem will be connections or grounding of the circuit between the sender and the gauge.

IMHO the gauge itself is least likely to be at fault, but it is the easiest to test so that should be done to rule it out.

I think the most likely cause after possible bad connections is the sender itself. Hopefully you can remove it without a great deal of disassembly of the surrounding structure. This is a moving part and is subject to failure. I had to replace mine at about 5-6 year old.

Attached are two documents that will explain the working of the gauge and the T/S procedure.

 

[Doug/Karen]

I am not familiar...

with the 340, but our 356 has a calibration option that allows us to periodically true up the read out.

 

[John T1594]

H340 Fuel Gauge

My fuel gauge does the same thing (2000 H340). Last time I filled up, the gauge read below 1/4 but the 30 Gal. tank took only 12 Gals. I will clean the contacts on top of the tank to see if that helps and replace the sending unit if necessary. Better to have too much fuel in your tank than run out and have to bleed the engine.

If you remove the center panel of the aft bulkhead in the aft berth on the H340, you can see the fuel and holding tanks. If you shine a flashlight on the side of the plastic tank, you can see the actual fuel level and calculate how much fuel (%) is left.

 

[Andy1237]

Caution! Gauge or vent could be your issue. This is my story: Gauge read empty, tank fills up with 2 gals. Hmm gauge broken and tank full, right? Wrong! Shortly later I ran out of fuel! Urrrrg. Add 5 gals, Bleed bleed bleed, and get things running. Fill tank? Not so fast-would only hold 2.5 gals more. What the..? Yesterday I added a measly 2 ga and the neck was full so I looked at the tank. Tank was swelled like a bloated catfish. Took off the vent hose and whooosh! So I removed the hose and fitting. It was clogged with spider/dirtdopper crap or something. After clearing the line (most in the elbow fitting a top) the tank sucked down the remaining diesel I had in can. Guage still barely moves above empty but I figure I only have approx 10 gal in a 30 gal tank. (this was on a Hunter 340)

Moral of this-if the gauge isn't working high to low, don't depend on the tank being full just because its won't take on any more fuel. Check your vent hose today.

 

[rfrye1]

probably the float assembly inside the tank. I never trust the gauge. I know how much fuel I use, always record engine hours when I fuel up so I know approx fuel used and how much is left. You need to pull your float/sending unit assembly out of your tank and check it. Probably gunked up. Just replace it, adjust the float for your tank levels.
Good luck. Bob.

 

[noprob2]

Use hours as gauge on340

Most reliable method is to track hours you can figure about .6 gph at 2500-2800 rpm on your 27 yanmar so 50 hrs is probably safe better yet track your engine and calculate it each time there
if you get nervous about it give yourself 10% slack the gauges are really not that accurate and I do not trust them
t

 

[André R.]

Here's my story. I own a H34 83, tried to take my tank out few years ago, couldn't do it the lazarette way cause i found out that, even if the top part is flat, and sides are square, the bottom is not. The stern end corners are the same depth, but the two other corners are not. The bottom follows the hull, so where the fuel line comes out it is deeper than the 3 other corners. Since the sender unit is at that end (in my case)and since it has an angled arm, when the float touches bottom, there's still fuel under it in the corner.
Basically, as other as mentioned, better have some left then run out, and calculating engine hours is a very good way.
I did not have a fuel gage nor hour meter when I bought the boat, but had them shortly after, can't spare them now. For what it's worth, at 2500-2700 RPM, I'm doing 1.5-1.6L/hour with a 3GM20F
Good luck
André
Wind Spirit 3
Lake Champlain