Twin Engines Fuel Consumption

[Momac]

I have been advised not to skimp on air filter changes in the interest of fuel economy.

Might it be worth checking or replacing the raw water impeller in the engine that runs warmer? Perhaps slight impeller damage would not be enough to see any temperature issue at slow speed.

 

[wayneakp]

fuel

Hi Greg
As you suggested I tried to keep an eye on boost pressure but as one gauge runs at 1 and the other nearly 2 - not sure what that means.
The one that runs high on boost uses more fuel but I wonder if that is a red herring. I know the dealer went through changing senders pipes etc when I bought the boat but they could not resolve it.

Looking back at my records for a refill from brim full after a trip, and by dipping tanks - Starboard 315 ltrs, Port 256 ltrs. Overall fuel consumption was what I expected - just seems more power is being provided by one engine.

I checked my tachos against a handheld laser thingy and they were way out. At cruise speed the thirsty engine was actually running 160 revs higher than the other - quite a lot I think for the relatively slow reving engines. The thirsty engine was obviously helping the lazy one

Problem was the error is not linear so I couldnt re-calibrate properly. In the end I calibrated to cruise speed. At tickover one tacho is well out but I figure cruise revs is more important.

Yesterday I ran to tacho and the cruise felt a lot smoother and just "right".

When you are down come and grab the laser thingy and see what results you get.

cheers

Wayne

 

[boatmike]

Hi Greg
As you suggested I tried to keep an eye on boost pressure but as one gauge runs at 1 and the other nearly 2 - not sure what that means.
The one that runs high on boost uses more fuel but I wonder if that is a red herring. I know the dealer went through changing senders pipes etc when I bought the boat but they could not resolve it.

Looking back at my records for a refill from brim full after a trip, and by dipping tanks - Starboard 315 ltrs, Port 256 ltrs. Overall fuel consumption was what I expected - just seems more power is being provided by one engine.

I checked my tachos against a handheld laser thingy and they were way out. At cruise speed the thirsty engine was actually running 160 revs higher than the other - quite a lot I think for the relatively slow reving engines. The thirsty engine was obviously helping the lazy one

Problem was the error is not linear so I couldnt re-calibrate properly. In the end I calibrated to cruise speed. At tickover one tacho is well out but I figure cruise revs is more important.

Yesterday I ran to tacho and the cruise felt a lot smoother and just "right".

When you are down come and grab the laser thingy and see what results you get.

cheers

Wayne

Wayne,
Assuming your tacho runs off alternator like most check your drive belt condition....
May be slipping under load

 

[bumpy_the_dog]

on every boat I have owned so far the port side engine always uses a bit more fuel than the starboard side. I could never find anything wrong and in the end put it down to the fact that the port side engine has to do more work because of the extra gear in the gearbox to make the props run the opposite way around to starboard engine. Don't forget that the "throttles" don't control the fuel usage but the engine speed. The governor in the injection pump controls how much fuel is used to maintain the desired speed. Check everything out but there is probably nothing wrong at all.

What a great forum this is, I would never have thought of that.

 

[SC500]

I had an interesting discussion with a marine engineer concerning fuel consumption deviation between engines and since running a Princess with twin Volvo's I would say he comments are verified in my instance.
We drive our boat at 6 knots when cruising due to speed limitations. What's obvious is the starboard engine nevr really warms to running temperature whilst the port engine reaches running temp pretty quickly. I am told this is due to the Stb engine heating the domestic water heating system and perhaps driving additional anciliary equipment.
Point is if an engine is not reaching it's optimum running temperature it will be running on partial cold start fuel map for longer, ie. consuming more fuel, hence this deviation.
When running our Princess at cruising speeds the engine coolant temperature balances out pretty quickly due to the amount of heat being generated.
I believe this is a normal status, more apparent when cruising at low speeds for reasons mentioned.

 

[Greg2]

Hi Greg
As you suggested I tried to keep an eye on boost pressure but as one gauge runs at 1 and the other nearly 2 - not sure what that means.
The one that runs high on boost uses more fuel but I wonder if that is a red herring. I know the dealer went through changing senders pipes etc when I bought the boat but they could not resolve it.

Looking back at my records for a refill from brim full after a trip, and by dipping tanks - Starboard 315 ltrs, Port 256 ltrs. Overall fuel consumption was what I expected - just seems more power is being provided by one engine.

I checked my tachos against a handheld laser thingy and they were way out. At cruise speed the thirsty engine was actually running 160 revs higher than the other - quite a lot I think for the relatively slow reving engines. The thirsty engine was obviously helping the lazy one

Problem was the error is not linear so I couldnt re-calibrate properly. In the end I calibrated to cruise speed. At tickover one tacho is well out but I figure cruise revs is more important.

Yesterday I ran to tacho and the cruise felt a lot smoother and just "right".

When you are down come and grab the laser thingy and see what results you get.

cheers

Wayne

Interesting that you have a bigger discrepancy with boost pressures Wayne. The fact that the engine with the higher pressure is the thirstier of the two tends to support the suggestion earlier in the thread that turbo boost is a good indicator of load. Hopefully your issue will have been resolved by re-calibrating the tachos. I'll take you up on the loan of the laser thingy to check our tachos when we are down.

I'll also check the alternator belts boatmike.

 

[wayneakp]

boost

Hi Greg

I am still not sure that the boost thing isnt a red herring. On the way back on Sunday I ran the engines at what I am confident are the same revs but the starboard boost was very high. I am awaiting on the manufacturers specs for boost pressure as I am starting to wonder if I have a wastegate issue??

cheers

Wayne

 

[Marsupial]

maybe something maybe nothing but we found that the engine connected to the calorifier always used more fuel, was thought to be because that engine took longer to reach operating temperature, BUT the amount of difference was not as high as stated in this thread.