Twin 6BTA – uneven fuel burn

[Mike Schmidt]

I have twin 330 6BTAs with one engine consistently burning about 20% more fuel. I verified the accuracy of the tachs and even have a tach synchronizer to make sure I’m running them at equal rpms. I’ve had this problem since I bought the boat 4 years ago and since then I’ve repitched the props to make 2850 WOT, replaced the airseps, adjusted valve lash, replaced the cutlas bearings, kept running gear and bottom clean, serviced the aftercoolers twice, changed fuel filters 1x/year, engine temps are the same, and all the other typical maintenance is kept up on.

What can cause this 20% discrepancy? It doesn’t seem to matter if I’m running mostly slow or fast.

Topic

[Carl Almond]

Have you considered doing an oil analysis? It is possible a comparison of the results between the two engines might give you a hint of what to check first. Standard things you might find are parts wearing more quickly on one motor versus the other, which would lead to an investigation of loading. Less obvious, you will be able to tell if one of the motors is getting significantly over-fueled, which then leads to leaky injectors, as suggested, or even differences in the pumps. You may have a local lab able to do the work, but if not, Blackstone Labs is used regularly for this. Testing both motors will cost you less than the price of 1 hour of a mechanics’ time and might save you considerably more.

[Clark Leighs]

Do you have EGT and Boost guages?   

  If one engine is working harder than the other then the boost and EGT reading should show a difference.  

It is not uncommon for one engine to use more fuel than the other even though they are “TWINS”.

However, 30 % does sound a bit rich.

And as Tony alluded to which side do you dock on?   Do you have a thief?       There are wire coils that can be installed in the fillers/hoses to defeat a siphon hose.

[Tony Athens]

Do you have easy to get to fuel fills?  Got locking gas caps?

[mark.boyle]

thanks for the reminder

But that is not the problem. Both engines seem to run just fine and we really don’t use the gen set. The port engine goes through 30 + % more fuel, in over a $1,000 dollars worth of fuel over 2 months, Lake Michigan to Mobile AL.

[Kyle Routh]

I realize this is an old thread – and my comment probably goes without saying, however just a reminder that many onboard generators are lined up to pull fuel from a specific fuel tank (e.g. port on my boat).  As such, except right after a fill-up, my port tank will always start dropping faster than the stbd due to running the generator frequently. 

This is probably not your case, and again, this is pretty obvious.  But sometimes new boaters might not realize things like this.

 

[mark.boyle]

Any new news on this topic

I have a similar situation with 370 6BTAs? Both seem to work just fine. Did you resolve the issue?

[donald roth]

You need to troubleshoot BOTH motors, the one with the high fuel burn may be running perfectly, but showing high fuel use as a result of having to bolster the poor performance of the other.
A good start would be to compare EGT/boost numbers of the motors before and after the anomaly in fuel burn.

[Francis Valerio]

Is this a new problem?

I think it could be a dinged prop

or

A bad injector (I understand you are making your RPMs but maybe a leaky injector)

[Author]

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