Engine consumes far less diesel than engine specification states..

[dingo]

Hi


I have an 1979 Leyland Thornycroft 154 (50HP) disel engine in my boat.
When I read the engine specifications I would expect a consumption of
between 6-8 Lit/Hour at the RPMs I am running at.

Can lower fuel consumption be caused by clogged air-filters etc?
What other causes could be likely?


Terje
Norway

[dingo]

Hi again

Some additional info ( I am reading Nigel Calder's Marine Diesel Engine and
trying to figure out this - but no luck yet ).

This is not something that has happende recently. I have had this boat for
about 2 years and I guess the engine performs as it did when I got it
(except when running at high RPM's which now seems to be a bit more painful
for the engine).

When running at > 2000RPM the engine also consumes quite a bit of oil
(lubricating). Max speed of engine should be around 3000 RPM, and the former
owner suggested normal operations at about 2600 RPM.

I seldom operate over 2200 RPM. If I run at 2500 for just a short while ( 1
minute ) I get a kind of "burned" smell. - The oil also smells burned.

Color of smoke: Hard do say, sometime white ( I live in a very humid
area ) - but never really blue.

I also run the engine at idle (RPM 1200-1500) for a couple of hours each
month. (I now know this is not very healthy for the engine).



Terje

Post by dingo
Hi
I have an 1979 Leyland Thornycroft 154 (50HP) disel engine in my boat.
When I read the engine specifications I would expect a consumption of
between 6-8 Lit/Hour at the RPMs I am running at.
Can lower fuel consumption be caused by clogged air-filters etc?
What other causes could be likely?
Terje
Norway

[william mason]

Post by dingo
Hi
I have an 1979 Leyland Thornycroft 154 (50HP) disel engine in my boat.
When I read the engine specifications I would expect a consumption of
between 6-8 Lit/Hour at the RPMs I am running at.
Can lower fuel consumption be caused by clogged air-filters etc?
What other causes could be likely?
Terje
Norway

I had a Leyland Thornycroft 230 (74hp) 4-cylinder,3.8 litres which
used 4 litres per hour at 1600rpm. At this engine speed the boat was
doing 6.5 knots and the noise level was fine. Extra revs increased the
noise level without any appreciable extra boat speed.
I would expect your consumption to be similar, allowing both for your
smaller capacity and your indirect injection fuel system ( the 230 is
direct injection).
Reading your other post, diesel engines need to work, the harder the
better. Running at 1200 rpm with no load on the engine is going to
polish the bores and ruin the rings. If you must run it, it would be
better to do it in gear and a bit slower.
Make sure your ropes are tight before you do though !
mvh

[b***@reading-college.ac.uk]

I assume this is a 2.2 or 2.5.

I just do not know how you can extrapolate from the graphs in mauals
etc that normally give teh consumption at full load to what you
actually get.

The consumption depends upon load and the load depends upon hull
design, water line length, water around and below the boat, clenliness
of hull, and most of all speed.

From virtually any engine in any boat from my particular main area of

experience I would expect about 1 to 2 litres per hour. This is because
the speed is low and the hulls long.

If you are staying within the hull design speed and not trying to get
the hull plaining then I see nothing wrong with "low" fuel consumption
- its what one should expect.

I can not comment on your hot smell, but from memory these engines
simply vented their crancase pressure into the engien room or air
cleaner, so again you are likley to have hot oil fumes around the
engine - you may also have a weep from the rocker cover gasket onto the
exhaust manifold ports.

I do not think you have too much to worry aboput on the glazing front
with BMC engines, but just make sure you get oil of a suitable lowely
spec. (probably API CC or CD) and giev the engiena thrash now and
again.

Tony Brooks

[Peter]

Good point on the type of oil to use. New engines requiring thin film modern
multigrades 10-20 grade etc.
Older engines need the oil that was around when they were new. HD 30 or
20-50 depending on whether you prefer detergent types or not.
Fuel consumption will also be dictated by the prop'. If it is too large or
small (pitch or diameter)
Peter

[dingo]

Hi


It sounds logic that the low consumption may be because the load is much
lower than theoretical max load. - I wont worry about this right now.

Oil fume venting sounds logical. Could I ask you to tell me what you mean
by "you may also have a weep from the rocker cover gasket onto the exhaust
manifold ports." ?? - My english is not quite up to this. (Weep=cry?) ?
`
The manual recommends (among others) the following lubricating oils:
Essolube HDX 20,
Shell Rotell S.oil 20W/20.
Is it so that some oil can be TOO modern and effective for an old engine?
What would the consequences be?

And by "giving the engine a trash now and then" - I guess you are asking me
to run at higher RPM's for short periods - and not only operate in the <2000
area ??


With regards
Terje

Post by b***@reading-college.ac.uk
I just do not know how you can extrapolate from the graphs in mauals
etc that normally give teh consumption at full load to what you
actually get.
The consumption depends upon load and the load depends upon hull
design, water line length, water around and below the boat, clenliness
of hull, and most of all speed.
I can not comment on your hot smell, but from memory these engines
simply vented their crancase pressure into the engien room or air
cleaner, so again you are likley to have hot oil fumes around the
engine - you may also have a weep from the rocker cover gasket onto the
exhaust manifold ports.
I do not think you have too much to worry aboput on the glazing front
with BMC engines, but just make sure you get oil of a suitable lowely
spec. (probably API CC or CD) and giev the engiena thrash now and
again.
Tony Brooks

[b***@reading-college.ac.uk]

Weep = UK engineering term for a small leak - more likley to cause
"damp" areas than "wet runs and drips".

Your oil specs are not specs, they are just brands and viscosity
rating. Viscosity is only a measure of how "runny" the oil is. I have
yet to see a marinisers engine manual that does not quote the API spec.
THis refers to how well the oil performs. The higher the API spec, the
more additives there are likely to be in it, and there is some
indication that those additives are implicated in bore glazing in
lightly loaded engines. It is probably best to ignore all the advice
from API and the oil vendors about modern oils specs superceeding older
one (They probably do in cars and trucks) and seek out a supplier of
oil to the spec originally recomended by the mariniser.

The glaze problem apperas to be related to too low a cylinder wall
temperature during combustion, so if you have to run your engines at
light load and low speed it may be best to run them at high speed/load
now and again. I can not say operated them at more then xxx rpm because
load also comes into it. Whenever I am on suitable water (rivers in my
case) I run my engine at maximum speed, taking care to stop opening the
throttle when the revs stop rising, and ensuring the revs are within
the "normal" maxium limits (most marine engines have maximum and
"emergency" power/rev maximums) for at least 15 minutes. I would have
thought that 2000rpm or so would be fine.

Hope this helps

Tony Brooks