Identicial Volvo Penta TAMD63P with different fuel burn rates

[Ariane]

Hi All

We have theoretically identical TAMD63Ps in our boat.

Had the misfortune to run out of fuel on one engine on a cross channel trip despite starting off with plenty of fuel for the trip with a comfortable reserve, or so we thought.

One engine performed as expected and we got back with a 3rd of a tank of fuel which is what I had calculated. The other ran dry about 5NM from home

Subsequently done lots of small trips and lots of dipping of tanks and inspecting of fuel levels and it seems one engine is burning nearly 20% more fuel than the other at the same revs.

Any one out there with any ideas as to what might me the cause.

The engine with the higher burn rate had it's injectors refurbished about 6 weeks before the cross channel trip to solve an excessive smoking problem.

Thanks

 

[James jameson]

The returns are running back to the respective fuel tanks ?

 

[scottie]

What if anything driven from greedy engine like extra or bigger alternator steering ing pump?

 

[Freebee]

yes check those returns my guess is they are tee'd together and feed back to one tank, but also check gearing and props identical

 

[Ariane]

Thanks for the replies..

Re the fuel returns, Port run to the Port tank and STB to the STB tank and the tanks do not cross feed.

Nothing extra on the STB engine that I am aware of. New alternator fitted 4 months ago but it was a like for like OEM replacement.

Steering is independent hydraulic system not engine driven.

The gen set does feed from the Port tank. It is Fischer Panda 6 but has only been run for 3 hours since the tanks were last filled to the brim so can't account for 200L of fuel hopefully.

Props are original so 21 yrs old so have to assume they are the same pitch etc although one may be out whack I guess??

Again gear boxes are original and have the same part numbers on and where last serviced in 2020 at the time new stainless steel shafts and seals where fitted.

 

[scottie]

Thanks for the replies..

Re the fuel returns, Port run to the Port tank and STB to the STB tank and the tanks do not cross feed.

Nothing extra on the STB engine that I am aware of. New alternator fitted 4 months ago but it was a like for like OEM replacement.

Steering is independent hydraulic system not engine driven.

The gen set does feed from the Port tank. It is Fischer Panda 6 but has only been run for 3 hours since the tanks were last filled to the brim so can't account for 200L of fuel hopefully.

Props are original so 21 yrs old so have to assume they are the same pitch etc although one may be out whack I guess??

Again gear boxes are original and have the same part numbers on and where last serviced in 2020 at the time new stainless steel shafts and seals where fitted.

The propellers may actually be different due to the handing required to stop you going round in circles
One will be left handed the other right if the gearboxes are actually handed rather than one effectively running in reverse . It is not considered ideal for the reduction ratio to be exactly 2:1 or 3:1 but 1:99:1 and 2:01: etc as this stops the wear
If they are the same part number it would suggest that this is not the case but?

 

[Whopper]

My guess is the returns aren’t as you say. Another option might be different tick over speeds but 200l is a lot!

 

[Chris_d]

Could be the engine with the higher burn rate and new injectors is doing all the work, change the injectors on the other engine

 

[Ariane]

The propellers may actually be different due to the handing required to stop you going round in circles
One will be left handed the other right if the gearboxes are actually handed rather than one effectively running in reverse . It is not considered ideal for the reduction ratio to be exactly 2:1 or 3:1 but 1:99:1 and 2:01: etc as this stops the wear
If they are the same part number it would suggest that this is not the case but?

HI Scottie.

Thanks for the reply. The props are mirror images of each other when you look at them so I suspect one is right handed and the other left handed. The gear boxes are IRM 220 A-1. The reduction ratio is 2.040:1 according to the plates on the top of both of them. Does that make any difference?

 

[Ariane]

My guess is the returns aren’t as you say. Another option might be different tick over speeds but 200l is a lot!

Hi Whopper

Thanks for the input. I have followed the fuels line from each engine back they are very neatly clipped together and the Port side run to and stop at the Port side tank and similarly the STB side. I can't find any evidence of pipework between the tanks or at the RACOR filters. Any clues as to what else I might look for or be missing?

 

[scottie]

No as said earlier you have either handed boxes or as in your case one effectively in reverse which is not a problem when set up correctly so don’t worry

 

[Ariane]

Could be the engine with the higher burn rate and new injectors is doing all the work, change the injectors on the other engine

Hi Chris

Thanks for the idea. I am not that technically minded but if one engine is doing more work than the other, would the boat not steer in the opposite direction to the more powerful engine?

 

[scottie]

Why were you looking at injectors there may be a problem there that deserves a further look
When running at constant speed and hands off the wheel are both showing same revs and boat running straight ?

 

[Ariane]

Why were you looking at injectors there may be a problem there that deserves a further look
When running at constant speed and hands off the wheel are both showing same revs and boat running straight ?

The injectors were looked at to cure an excessive smoking problem. White / Grey smoke on startup that did not really improve with any length of run time.
Sadly the STB tacho is wayward. Although it is not the tach it is in the wiring somewhere. When we purchased the boat the STB tacho would give consistent readings at tickover then the needle would start to swing more and more violently and eventually pack up at 3/4 throttle.
We initially assumed it was a fault in the alternator which is why a new alternator was fitted. The problem didn't go away unfortunately.
Oh and before we replaced the alternator we swapped the tachos from Port to STB and the problem remained in STB so it wasn't the actual dial causing the issue.
I drive the boat by setting the rudder amidships then setting 16 - 1700 RPM on port and opening the STB throttle till the boats runs straight. Then adjust the throttles as little as possible.
I have just purchased a pair of digital tachos with HALL sensors to fit on the front wheels to get a true RPM reading. But I do need to spend time trying to find what I expect to be a corroded wire somewhere between the alternator and the gauge.

 

[Whopper]

Hi Whopper

Thanks for the input. I have followed the fuels line from each engine back they are very neatly clipped together and the Port side run to and stop at the Port side tank and similarly the STB side. I can't find any evidence of pipework between the tanks or at the RACOR filters. Any clues as to what else I might look for or be missing?

Our setup has valves that can divert return fuel to its tank of origin or to an individual tank of choice. Do you have something similar? Could be worth experimenting with the valves.

 

[Chris_d]

The injectors were looked at to cure an excessive smoking problem. White / Grey smoke on startup that did not really improve with any length of run time.
Sadly the STB tacho is wayward. Although it is not the tach it is in the wiring somewhere. When we purchased the boat the STB tacho would give consistent readings at tickover then the needle would start to swing more and more violently and eventually pack up at 3/4 throttle.
We initially assumed it was a fault in the alternator which is why a new alternator was fitted. The problem didn't go away unfortunately.
Oh and before we replaced the alternator we swapped the tachos from Port to STB and the problem remained in STB so it wasn't the actual dial causing the issue.
I drive the boat by setting the rudder amidships then setting 16 - 1700 RPM on port and opening the STB throttle till the boats runs straight. Then adjust the throttles as little as possible.
I have just purchased a pair of digital tachos with HALL sensors to fit on the front wheels to get a true RPM reading. But I do need to spend time trying to find what I expect to be a corroded wire somewhere between the alternator and the gauge.

If you don't know that both engines are running at the same rpm that would explain the problem and that you have one engine not producing full power. Generally fuel consumption on twins is always slightly different, but not 20%. Think you should get the tachos working first.

 

[volvopaul]

The injectors were looked at to cure an excessive smoking problem. White / Grey smoke on startup that did not really improve with any length of run time.
Sadly the STB tacho is wayward. Although it is not the tach it is in the wiring somewhere. When we purchased the boat the STB tacho would give consistent readings at tickover then the needle would start to swing more and more violently and eventually pack up at 3/4 throttle.
We initially assumed it was a fault in the alternator which is why a new alternator was fitted. The problem didn't go away unfortunately.
Oh and before we replaced the alternator we swapped the tachos from Port to STB and the problem remained in STB so it wasn't the actual dial causing the issue.
I drive the boat by setting the rudder amidships then setting 16 - 1700 RPM on port and opening the STB throttle till the boats runs straight. Then adjust the throttles as little as possible.
I have just purchased a pair of digital tachos with HALL sensors to fit on the front wheels to get a true RPM reading. But I do need to spend time trying to find what I expect to be a corroded wire somewhere between the alternator and the gauge.

The alternator does not give the rpm signal to Rev counter , 63p has its own sender .

 

[Ariane]

The alternator does not give the rpm signal to Rev counter , 63p has its own sender .

Thanks Volvopaul

although now I am confused. On both engines there is a wire from the W+ stud on the alternator which disappears into the wiring loom of the engine. I assumed, as per my old Sabres, that this was generating the RPM signal for the Tacho. If it isn't, any idea what purpose it serves and where on the engine the sender is as I guess that is the cause of the wayward tacho. If I can get the the tachos sorted I might get somewhere with solving my fuel burn discrepancies

 

[david_bagshaw]

Over how long to develop the 200 ltr difference?

My thoughts, are one engine isnt using as much power, so I would have both engines props checked. But first check for barnacles on props, as one side might be fouled? and thus draw less power.

if over a long time does one engine provide all the domestic services battery bank charge?

 

[Ariane]

Over how long to develop the 200 ltr difference?

My thoughts, are one engine isnt using as much power, so I would have both engines props checked. But first check for barnacles on props, as one side might be fouled? and thus draw less power.

if over a long time does one engine provide all the domestic services battery bank charge?

Hi David

The 200 ltr difference was over a single 6 1/2 hour run from Alderney to Southampton.
Left Braye with full tanks ~ STB ran dry 5 miles from home and Port still had 200 litres in it