Uncalibrated Fuel gauge - Volvo Penta.

[Sticky Fingers]

Hi folks. My 1999 boat has 2x VP TAMD73P engines, drawing fuel from 2x 700 litre tanks. The tanks are not interconnected. Each has a fuel gauge which appear to be functioning properly. All very conventional, except for the fact that the gauges have no obvious calibration to them. See pic below. Question is, at what % point does the red zone kick in?

 

[Pinnacle]

Why not run the tank down to the beginning of the red zone and then brim. That way you will know how many litres remain in the tank when you enter the red. (The answer may be different for each tank).

 

[rafiki_]

G, fuel gauges tend to be non-linear. My experience is that half tanks indicated are nearer to 1/4.

 

[Sticky Fingers]

Why not run the tank down to the beginning of the red zone and then brim. That way you will know how many litres remain in the tank when you enter the red. (The answer may be different for each tank).

Hi P, thank you - that’s the best method that I’ve come up with so far, usefully close to that point on one of the two tanks right now so when I refuel in the next few weeks I could do this.

 

[Sticky Fingers]

G, fuel gauges tend to be non-linear. My experience is that half tanks indicated are nearer to 1/4.

That would definitely be a worry if true, I’d kind of hoped it was pessimistic rather than optimistic…

 

[rafiki_]

That would definitely be a worry if true, I’d kind of hoped it was pessimistic rather than optimistic…

As Pinnacle says, you need to brim at some time. Is it possible to get a dipstick through the filler?

 

[Sticky Fingers]

As Pinnacle says, you need to brim at some time. Is it possible to get a dipstick through the filler?

True.

Dipstick, pretty much impossible, I had a look at the filler pipe runs, and it runs from the deck fitting, turns 90 degrees then laterally under the deck then another 90 degree turn into the top of the tank. Pretty much impossible I’d say. I wanted to put an endoscope in, not possible.

 

[Refueler]

Hi P, thank you - that’s the best method that I’ve come up with so far, usefully close to that point on one of the two tanks right now so when I refuel in the next few weeks I could do this.

Instead of refueling ..... you can pump from one tank to the other .....

Pump out the lesser tank to the other till gauge hits red line. Then pump out to containers. This will give you a reference volume for the red line.

With one tank now in practical terms empty - you can now pump from other tank into the empty tank till it hits red line start again. You now have a reference volume change in the other tank ...

Return container fuel to which tank you prefer making not of how much each tank and the change in reading on gauges.

Now when refueling - instead of just topping off tanks ... actually work to a system of xx litres each time - t build up knowledge of the tanks volume vs gauge reading.

 

[Sticky Fingers]

Thank you, that would work, probably more faffing about that I’m ready for, but a neat idea.

 

[Daydream believer]

Why not just completely empty one tank into the other. Then fill until the red line (tap the guage to see if the needle jumps)& you know how much that level is. Make a note in the log. Then watch the level on the guage change as you complete filling. Mark the guage at, say XX litres, & log it in case you forget. . Repeat doing ,say, 2 indelible marks. Then note how many litres fill the tank. Not all tanks take what the supplier claims.

 

[Greg2]

True.

Dipstick, pretty much impossible, I had a look at the filler pipe runs, and it runs from the deck fitting, turns 90 degrees then laterally under the deck then another 90 degree turn into the top of the tank. Pretty much impossible I’d say. I wanted to put an endoscope in, not possible.

Is there access to top of the tanks? Just thinking that it might be possible to remove a fitting (e.g. fuel gauge sender, fuel return) so that you can get some kind of dipstick in. Could be a fairly straightforward way of finding out how much is in the tanks,
.

 

[Sticky Fingers]

Is there access to top of the tanks? Just thinking that it might be possible to remove a fitting (e.g. fuel gauge sender, fuel return) so that you can get some kind of dipstick in. Could be a fairly straightforward way of finding out how much is in the tanks,
.

I think that’s possible by removing the saloon furniture and floor panels completely; there may even be a small panel above the sender unit. I’ll have a look next visit. . The tanks are located fully outboard P&S, ie partially under the side decks so it’s not at all easy to get to the top.

 

[kashurst]

If you can get at the fuel tank senders KUS, WEMA or similar linear senders are almost certainly available to suit your tank depth.
They work much better than the old fashioned swing arm mechanisms and in boat terms pretty cheap upgrade. You just need to check the resistance which is very likely European spec resistance 0 -190 ohms and tank depth immediately below the sender hole.

 

[MapisM]

G, fuel gauges tend to be non-linear. My experience is that half tanks indicated are nearer to 1/4.

Seconded. I've seen also the opposite, but either way, IMHO an accurate fuel gauge for boats is yet to be invented.

Not sure of how easy (or not) it is on the OP boat to fit sight gauges, but if the tanks pickup is somewhere along their bottom, it should be an easy and inexpensive job, which I can't recommend highly enough.
The builder of my second to last boat (who came from a commercial heritage) never fitted any dash gauge in their boats - only sight gauges.
Suffice to say that after experiencing it, fitting sight gauges on my current boat was right at the top of the jobs list to make after buying her.

 

[PaulRainbow]

If you can get at the fuel tank senders KUS, WEMA or similar linear senders are almost certainly available to suit your tank depth.
They work much better than the old fashioned swing arm mechanisms and in boat terms pretty cheap upgrade. You just need to check the resistance which is very likely European spec resistance 0 -190 ohms and tank depth immediately below the sender hole.

I recently fitted all new KUS guages at the lower helm (upper helm is digital over N2K), tanks are only a few years old, so i suspect linear senders. The gauges are certainly pretty accurate down to at least 1/3rd of a tank, not been any lower to check.

 

[Refueler]

700L tanks ..... not a small simple affair to sort.

The transfer suggestion I made earlier is how we do large transit tanks of 00's ... 000's tons ... (commissioning is by "Tank Strapping" .. used to be by physical strap round tank - hence the name - today is by radar 'cars' etc.) but later checks can be by physical filling / transfers etc.

 

[oldgit]

Why not run the tank down to the beginning of the red zone and then brim. That way you will know how many litres remain in the tank when you enter the red. (The answer may be different for each tank).

Did that shortly after buying the boat. A single 1000L tank.
A rule of thumb, knowing your average fuel consumption in LPH / RPM.
A third of the tank to get you to your destination.
A third for any diversion
A third just in case. ?

 

[Sticky Fingers]

I recently fitted all new KUS guages at the lower helm (upper helm is digital over N2K), tanks are only a few years old, so i suspect linear senders. The gauges are certainly pretty accurate down to at least 1/3rd of a tank, not been any lower to check.

These are the original tanks and I assume OEM senders. I don’t really want to go to the complexity of replacing gauges and senders etc, just would like to know how much I have left when it goes into the red. Pinnacle’s suggested approach is the easiest to do for sure, that’s where I will start I I think/

 

[Farmer Piles]

I have had just the same issue with my gauge like yours but mine works the other way - the edge of the red is at least a quarter full if not more. At the top end it is equally vague. The tank has no taper with a flat bottom and is a U shape wrapping around the engine with negligible clearance above it. It should be a linear process to measure the contents.
I have a single KAMD44 and I reckon on it using about 40lph when cruising. Not sure how accurate that is, maybe I should fit a flow meter?

 

[robrennie]

Instead of refueling ..... you can pump from one tank to the other .....

Pump out the lesser tank to the other till gauge hits red line. Then pump out to containers. This will give you a reference volume for the red line.

With one tank now in practical terms empty - you can now pump from other tank into the empty tank till it hits red line start again. You now have a reference volume change in the other tank ...

Return container fuel to which tank you prefer making not of how much each tank and the change in reading on gauges.

Now when refueling - instead of just topping off tanks ... actually work to a system of xx litres each time - t build up knowledge of the tanks volume vs gauge reading.

Every day is a school day…..

Putting a fixed amount of fuel in and reading of the gauge difference rather than brimming is genius…

And an opportunity to waste hours of time on a spreadsheet