F36 KAD44s unequal fuel use

[Sneds]

Starboard fuel gauge on around 70% and probably reading a little more than I would expect, port gauge nearly on the red at around 30% and a little less than I would expect!
Could one engine be using nearly twice as much fuel as the other or do I have a dodgy gauge?
The boat is quite new to us and I remember when we got it both gauges were showing, almost equally, just on the red.
Any ideas?

 

[Somerset Jim]

Iain, have you checked that the returns for each engine are feeding back to their respective tank. It could be that both engines are returning to one tank. Even with this being the case I wouldn't expect it to make that much of a difference.

Additionally it may be that the gauges are calibrated slightly differently. Ours has one gauge that shows just below full and the other just above full when both tanks are brimming.

 

[kashurst]

If one engine was using twice as much as the other you would have a cloud of black smoke behind you.
Check out the gauges and sender's. The old swinging arm style transducers can be misleading. I like the newer vertical sender's with a ring magnet that slides up and down. Much more linear and believable. +1 check out the return valves etc.

 

[Sneds]

Thanks, fuel feed and return valves are in the correct position but I'll double check they are labelled correctly!

 

[benchmark]

Manual/analogue float guages are notorious for being inaccurate after some time. The easiest diagnosis will probably be to switch instrument wires from each guage on one tank to the other and see what happens.

 

[Momac]

As said it seems common for the Volvo Penta fuel gauges to be inaccurate.
I have similar situation at the moment on my F33 and will see how much fuel goes in when I fill up.

 

[simonfraser]

yeh my VP gauge none too reliable either.

what would be a good substitute ?

 

[rafiki_]

Iain, if you recall last summers epic trip, Rafiki's std tank emptied about 20% quicker than the port. it could be that the std tacho reads differently? No smoke. No real issues as a result.

 

[snowbird30ds]

I have a pair of tmd41's and the port engine always uses more fuel (not 50% though) and I get no smoke, good point about checking the tachos, my fuel gauges are fairly good as I have sight gauges too but don't go right to the top and the red is not a reserve it's there to tell you it's already stopped. (guess how I found out)

 

[kimhollamby]

Definitely check they are labelled correctly. I had the experience of them not being labelled correctly on an F36 and we wound up actually filling one tank almost to overflow when running on one engine.

 

[BruceK]

Iain, if you recall last summers epic trip, Rafiki's std tank emptied about 20% quicker than the port. it could be that the std tacho reads differently? No smoke. No real issues as a result.

Ditto. I had this problem last year. Dedicated tanks and one engine was using 25 - 30% more fuel. One alternator had been changed and the pulley was ever so slightly smaller. New pulleys. Calibrated the tacho's against a strobe tacho and everything returned to normal. One engine was obviously carrying more load. Another factor for me is one tank is 30% bigger than the other to supply the genny and I have no balance pipe between tanks. However when I fuel up to the brim now the same amount within 20 litres is going into each tank.

 

[rafiki_]

Ditto. I had this problem last year. Dedicated tanks and one engine was using 25 - 30% more fuel. One alternator had been changed and the pulley was ever so slightly smaller. New pulleys. Calibrated the tacho's against a strobe tacho and everything returned to normal. One engine was obviously carrying more load. Another factor for me is one tank is 30% bigger than the other to supply the genny and I have no balance pipe between tanks. However when I fuel up to the brim now the same amount within 20 litres is going into each tank.

Interesting. I changed an alternator last year, but retained the pulley. Worth investigating.