Diesel engine running schedules

[lumphammer]

I was reading a post about the dangers of running a yacht diesel engine for long periods at a constant rpm.
Do you have a routine when running under engine? How long is a long time to run at constant rpm? How much do you need to change the revs by to stop it being a constant rpm?

 

[Appledore]

Hi,

I found this some time ago in respect of my Yanmar 1 GM 10 engine:

"Cruising speed 3400 rpm for less than 90% of engine use, 3600 for only 10% in an hour"

The top rpm for this engine is 3,600 rpm, as shown above. The recommendation is to use the 'cruising speed most of the time, but this should be increased to full revs, as shown, each hour of running. Hope this might help until someone else can offer more advice.

Geoff

 

[Tranona]

The 1GM is unusual in that you have to run it hard to get any power out of it, so 3000+ is common cruising revs.

However for larger multicylinder 15-40 hp, most have maximum revs of 3200 or 3600 and the recommendation is to run at +/- 70%, so in the range of 2100-2500 rpm for cruising speed with bursts of 3000+ periodically. The important thing is to put enough load on the engine to avoid such things as bore glazing, and provided the boat has the correct prop, these revs will do that and give a good cruising speed of 5 knots+.

 

[RupertW]

Diesel engines especially ones with and industrial base design like Yanmar are expected to run at constant revs for 10s of thousands of hours. As people have said above it should not be above the recommended limits for more than short periods.

I am never totally sure about the load issue - people who know far more than me say it is true so it must be but I haven't known an engine in practice that has had glazed cylinders even when mostly run in neutral and owned for many years. It wasn't until I started sailing in the Med that the hours in gear exceeded the hours in neutral and even now it's a fine line as our fridge is only engine run so both in the marina and at anchorage we need to run it to keep things cool.

 

[Tranona]

Running your fridge is putting load on the engine.

 

[vyv_cox]

The Yanmar workshop manual says to rev the engine in neutral from low to max revs 5 times every two hours. I have to say that I don't think I have ever heard any other manufacturer recommend revving in neutral. My own practice is to run to maximum revs (3600) for five minutes or so every couple of hours. Initially a great deal of smoke is emitted from the exhaust but after a minute or two this disappears. I then return to my normal cruising revs of around 2000.

 

[prv]

Diesel engines especially ones with and industrial base design like Yanmar are expected to run at constant revs for 10s of thousands of hours.

+1. My engine was designed for use in generators - indeed we had a couple of gensets delivered at work for a project and the diesel half of the set looked extremely familiar .

Standard generators have to run at constant revs to generate AC at a particular frequency.

Pete

 

[johnalison]

I have seen a recommendation in the Volvo instructions to put the engine in neutral every ten hours, I think, but this was specifically for those with shaft drive rather than saildrive.

My 2030 has max revs of 3400. It runs more smoothly above 2000, so my usual cruising revs are 2400-2700. I don't have schedule for giving it a break but normally have to stop from time to time to check the raw water filter. My hour meter has stopped reading but I think we have done something over 3000 hrs and the engine starts on the button and uses a minimum of oil.

 

[jdc]

I run my kubota engine at constant revs, usually at 1400 rpm, for sometimes days at a time. Like this I can just get 1000 miles range although it's never happened that I have had to motor more than 500 miles in flat calm. I can see no reason whatsoever to make me change revs except that running with little load is reputed to be deleterious, in which case the advice should be to run at high power every so often (as Vyv says in his post above). Whether that should be every 2 hours, or every 48 (roughly and as and when I remember / can be bothered) I have no idea. So far, after 2500 hours the engine seems only just run in, has clean oil and is consuming only about 0.15 g / kwHr (which is really as low as any engine gets, being less than 0.2 litres per year for most yacht engines: you wouldn't actually notice this). So my lackadaisical 48 hours seems ok, or at least I've got away with it.

 

[superheat6k]

Generally Diesel engines prefer to be worked hard, so occasional bursts at full or close to full load are good because below ~2/3 load they start to form deposits that can harden and then do not burn off so easily, and at lower power can glaze the bores, which reduces cylinder lubrication efficacy.

Turbo chargers are also subject to deposit build up, so a good hard run at least once per trip is IMHO a good idea, and I like to run at least a mile at high revs / power each time I go out.

On a boat engine the propellor load is proportional to the speed, so varying the speed is the only way to vary the load. However, on a (non-inverter) generator they always run at constant speed because the output frequency is controlled by the shaft speed. On a 2 pole alternator 50hz = 3000 rpm, on a 4 pole 50hz = 1500 rpm. Load is varied by the electrical devices being used.

 

[parbuckle]

+1. My engine was designed for use in generators - indeed we had a couple of gensets delivered at work for a project and the diesel half of the set looked extremely familiar .

Standard generators have to run at constant revs to generate AC at a particular frequency.

Pete

+1 The Perkins 100 series engine is at the heart of the Perama marine version these basic units are used in generators and air compressors etc that are run at constant revs although they normally have different camshafts to suit the revs required e.g. 2600 or 3000 instead of 3600 they are expected to give 10000 hrs service running at a constant speed although I imagine the changing load will slightly vary the RPM.
I would be more wary of running a marine engine at tickover for long periods though,

 

[geem]

We run our 4.4litre Perkins at 1200 rpm. That gives us 6kts in calm seas. Maximum revs is 2200 rpm. 1200 rpm coincides with maximum torque for the engine. We recently ran none stop at these revs for 3 days without change. Perkins rate the engine as suitable for commercial use and spec high quality oil with 500 hrs between changes. Works for me

 

[Matthijs Siljee]

It is probably all quite relative. And running regimes may vary between situations and circumstances. My mechanic explained that diesel engines are designed for a very long service life, often longer than most pleasure boaters would clock up, so a dramatic shortening of service between reconditioning may be seldom experienced. He says that diesel engines are designed to run hot. Internal combustion needs something to push against, and part of the energy is converted to heat. The heat helps with a more complete burning of the diesel. In a colder run, under-loaded engine part of the unused diesel gets up to mischief: polished carbon deposit, maybe dissolving some oil, soot. Glazing the bores is not the only issue. Cylinders, pistons, rings, valves and bearing surfaces get the correct shape and tolerances at that intended high working temperature. We run the engine in gear at the marina.