Diesel Consumption through the roof

[Colvic Watson]

Despite antifouling and ten minutes of daily Scrubis we see fuel consumption ticking up all summer. One of the culprits is the prop where a very small level of crustacean fouling requires a significant increase in revs to achieve the same speed.

I can’t remember, can someone remind me the different diagnosis for white, blue and black smoke?

 

[vyv_cox]

I can’t remember, can someone remind me the different diagnosis for white, blue and black smoke?

White smoke is excessive unburnt fuel, blue is burning oil due to wear of piston rings or valve oil seals, black is caused by carbon in the exhaust, produced by overfuelling due to fouling of underwater surfaces or by carbonate fouling in the exhaust elbow.

 

[PaulRainbow]

White smoke is caused by unburnt fuel in the combustion chamber. It can occur due to poor starting but the smoke usually clears in a minute or so in that case. It can also be due to faults or wear in the injector pump resulting in excessive fuel being injected.

The symptoms of a partially blocked filter are unmistakeable - the engine will rev in neutral but not in gear. In severe cases it will stall as soon as the gear lever is engaged. The filters are located before the injector pump and cannot result in excessive fuel being delivered by it.

I suggest there is a problem somewhere in the injector pump. White smoke can be caused by a fouled or sooted injector but this is unlikely to have led to excessive fuel consumption.

There cannot be an 'imbalance' in the air to fuel ratio. Air in a diesel is at full flow always, unlike a carburated petrol engine, it has no butterflies. Fuel is added directly into the cylinder by the injectors to increase speed and power.

Some diesel engines have a throttle butterfly in the intake manifold. (doesn't change any of your advice).

 

[B27]

...

I suggest there is a problem somewhere in the injector pump. White smoke can be caused by a fouled or sooted injector but this is unlikely to have led to excessive fuel consumption.
...

A fouled injector may inject fuel in a jet rather than a mist. So not all of it gets burned. The injector pump injects as much as the engine needs to hold the RPM set by the 'throttle'.
If the injector is fouled and not all the fuel is burning, the pump will add more to compensate.

Other possible causes may include injector pump timing and water in the fuel.

OTOH the 'smoke' may be steam, in which case the cooling system needs looking at. Loading due to fouling or a strong headwind might make a 'marginal' cooling system show symptoms.

 

[vyv_cox]

Some diesel engines have a throttle butterfly in the intake manifold. (doesn't change any of your advice).

Yes, my old BMC 2.5 did but it was so ancient as to be discounted

 

[vyv_cox]

A fouled injector may inject fuel in a jet rather than a mist. So not all of it gets burned. The injector pump injects as much as the engine needs to hold the RPM set by the 'throttle'.
If the injector is fouled and not all the fuel is burning, the pump will add more to compensate.

Other possible causes may include injector pump timing and water in the fuel.

OTOH the 'smoke' may be steam, in which case the cooling system needs looking at. Loading due to fouling or a strong headwind might make a 'marginal' cooling system show symptoms.

Having experienced white smoke due to excessive fuel and steam due to water, I would say it is impossible to confuse the two. My excessive fuel incident was in Port Dinorwic outer dock, where the amount of smoke and its persistence were embarrassing.
Steam disappears in seconds

 

[Supertramp]

Last week I had white smoke from the exhaust so changed both fuel filters and that fixed the problem. However, since then our fuel consumption has gone up from about 2.4litres per hour to 3.4 litres per hour. There are no fuel leaks in the system. Both supply and return hoses were changed last year.

Both filters were catching black specs of whatever and were changed last winter. The boat has done a lot of miles this year. Almost 1000 and maybe 250 of those

Last week I had white smoke from the exhaust so changed both fuel filters and that fixed the problem. However, since then our fuel consumption has gone up from about 2.4litres per hour to 3.4 litres per hour. There are no fuel leaks in the system. Both supply and return hoses were changed last year.

Both filters were catching black specs of whatever and were changed last winter. The boat has done a lot of miles this year. Almost 1000 and maybe 250 of those under engine.

Not sure that 1000 miles and 250 miles motored is very much in engine terms. I measure fuel consumption over a season and about 100 hours (or 450 miles) motored. I wouldn't check over days unless I could go full to full on the tank. I am certain my fuel consumption dramatically increases with the engine under load in head seas versus calm motoring. If your only symptom now is consumption I would measure over longer periods tank full to tank full, if you can.

 

[B27]

Not sure that 1000 miles and 250 miles motored is very much in engine terms. I measure fuel consumption over a season and about 100 hours (or 450 miles) motored. I wouldn't check over days unless I could go full to full on the tank. I am certain my fuel consumption dramatically increases with the engine under load in head seas versus calm motoring. If your only symptom now is consumption I would measure over longer periods tank full to tank full, if you can.

The only time I would be trying to measure fuel consumption would be if I was worried I didn't have enough reserve or if my engine started smoking or otherwise misbehaving.

Mostly it's meaningless, it varies according to how much of a rush we are in, wind and sea against us or whether the main is helping or merely damping the motion.

 

[Supertramp]

The only time I would be trying to measure fuel consumption would be if I was worried I didn't have enough reserve or if my engine started smoking or otherwise misbehaving.

Mostly it's meaningless, it varies according to how much of a rush we are in, wind and sea against us or whether the main is helping or merely damping the motion.

Agreed, but it's useful to know for planning long trips or if the tank will see the season out. Mine is remarkably consistent year to year.

 

[Tinto]

We have been out since early May so, I am well used to how much it drops over so many miles. So I have a better handle on it than most. Fairly sure I have some prop fouling.

We came round the Mull of Kintyre today and had to motor a lot of it. From heading south to east to north we were head to wind, but with the tide. so the consumption today was much better, which is good to know.

My question was to ascertain if there could be any other factors other than fouling if prop or hull, but it seems not. So I am happy with that. Living with a problem is a lot easier when you know the cause,
Especially when you have a 50mile passage around the Mull in from to you.

 

[B27]

The white smoke would concern me far more than an extra few litres of diesel.

 

[RunAgroundHard]

We have been out since early May so, I am well used to how much it drops over so many miles. So I have a better handle on it than most. Fairly sure I have some prop fouling.

We came round the Mull of Kintyre today and had to motor a lot of it. From heading south to east to north we were head to wind, but with the tide. so the consumption today was much better, which is good to know.

My question was to ascertain if there could be any other factors other than fouling if prop or hull, but it seems not. So I am happy with that. Living with a problem is a lot easier when you know the cause,
Especially when you have a 50mile passage around the Mull in from to you.

Your posts describe intermittent high fuel consumption, sometimes over short durations. Surely fouling would mean there was always a higher than usual fuel consumption.

I have a different motor, Perkins 4236, but old tech, I know my fuel system is good and there is no fouling, in all weathers and wind states, bang on 0.75 gph. When I fill up, always get what I expect.

I think there have been two significant clues, white smoke, intermittent high fuel consumption. Previous comments on faulty injection pumps, maybe injectors themselves, could cause your problem when all the other stuff is stripped away.

I have had clouds of white smoke blow out an exhaust pipe of a car due to a faulty fuel pump, intermittently, all the lanes of a motorway blanketed in white smoke. When I bead my diesel engine, after filter changing, I get a big white cloud that disperses when the engine starts, same thing, smaller volume.

Good luck with your investigations.

I would be looking at having the fuel pump serviced, or injectors, after a call with a competent marine mechanic at Kip or Largs (others as well). I have owned old, classic tractors, an injector service does wonders for the health of the engine. Also, you anchor a lot, or moor, do you not look under the hull and check from time to time. I know I do, just to see if there is anything obvious changing. For example, the black Velox paint on my prop is wearing, I can see the bronze colour shining through.

 

[Tinto]

Lots of people fixated on white smoke. If you read post #1 again you will see that the white smoke issue was fixed by changing the fuel filters.

 

[Tinto]

Your posts describe intermittent high fuel consumption, sometimes over short durations. Surely fouling would mean there was always a higher than usual fuel consumption.

I have a different motor, Perkins 4236, but old tech, I know my fuel system is good and there is no fouling, in all weathers and wind states, bang on 0.75 gph. When I fill up, always get what I expect.

I think there have been two significant clues, white smoke, intermittent high fuel consumption. Previous comments on faulty injection pumps, maybe injectors themselves, could cause your problem when all the other stuff is stripped away.

I have had clouds of white smoke blow out an exhaust pipe of a car due to a faulty fuel pump, intermittently, all the lanes of a motorway blanketed in white smoke. When I bead my diesel engine, after filter changing, I get a big white cloud that disperses when the engine starts, same thing, smaller volume.

Good luck with your investigations.

I would be looking at having the fuel pump serviced, or injectors, after a call with a competent marine mechanic at Kip or Largs (others as well). I have owned old, classic tractors, an injector service does wonders for the health of the engine. Also, you anchor a lot, or moor, do you not look under the hull and check from time to time. I know I do, just to see if there is anything obvious changing. For example, the black Velox paint on my prop is wearing, I can see the bronze colour shining through.

white smoke issue was fixed prior to noticing increased fuel consumption. This winter I will clean the injectors and have my fuel injection pump reconditioned.

 

[B27]

Lots of people fixated on white smoke. If you read post #1 again you will see that the white smoke issue was fixed by changing the fuel filters.

Fair enough.
Bit unsure how that worked, maybe contaminated fuel.

I'd give it a good test under load before going the other side of Mull, but I expect you've done that.

 

[rotrax]

I had severe white smoke on a Bukh DV20. It proved to be leaking injector nozzles.

Simple fix, albeit expensive.

 

[Colvic Watson]

White smoke is excessive unburnt fuel, blue is burning oil due to wear of piston rings or valve oil seals, black is caused by carbon in the exhaust, produced by overfuelling due to fouling of underwater surfaces or by carbonate fouling in the exhaust elbow.

Thank you, really helpful.

 

[vyv_cox]

Thank you, really helpful.

There is a more comprehensive discussion here Engine faults

 

[Refueler]

mmmm just adding - Black Smoke can be when like my engine - when full throttle and fuel delivery is excessive ... basically blowing loads of half burnt carbon full fuel / smoke out ...
Obviously something I do not do often - I just give it max occasionally to clear the 'crap' out of her !!

 

[Tinto]

and the culprit was a fouled prop. Covered in sealice. Didn't take long to chip it off once dried out.