Warming diesel engines

[cliff]

Re: Not paranoid

My next job is to pull the tank out and clean it out - give it a good steam clean then change the fuel lines. Bugs, possibly.

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[bedouin]

If I start my diesel from cold and immediately throttle back to the neutral position on the Single Lever control it stalls - and even when it will tick over in neutral without stalling it needs to warm up a little more before it can provide enough power to manouevre adequately (possibly the cold-start device needs adjusting).

So I tend start the engine about 5 minutes before departure - to try to leave earlier than that can be a hair-raising experience from a tight berth or mooring in adverse conditions.

This also has the added advantage that it ensures that fuel is flowing and that there aren't any blockages in the fuel system.

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[jimi]

Can empathise about the blockage or air lock bit as I have been caught out there before. tend to run for c 5 mins before leaving to ensure no airlocks downstream of lift pump.

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[Robin]

I always start our engine in neutral position/tickover, no open throttle, thats a Yanmar 44 but I doid the same on our last boat with a Volvo 50. Both start even midwinter with no need for preheat and engaging gear does not stall the engine. Perhaps your idle speed is just a tad slow?

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[ALEXD]

What about charging batteries and heating water, when you don't need propulsion?

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[bedouin]

Different engines have different methods of starting. I follow the manufacturers instructions which is 1/2 - 2/3 throttle and the cold start device - and even the diesel in my car needs preheat to start easily.

I would guess that the two engines you mention have more cylinders and more power than my venerable MD2B (and probably have a faster idle speed as well).

Idle speed is fairly low - but fine when the engine is warm. However it is a large lump and takes some time to get to that temp.

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[KevB]

I think it's to stop undue engine wear. Isn't it a fact that 80% of engine wear happens in the first 10 minutes? Putting engines under load before they are warmed up isn't good. Wait for the oil to become nice and slippery and off you go.
Turbo's definitely need cooling down before switching off the engine otherwise the oil burns onto the bearings and shafts.

Some engines don't run to well till they have warmed up - wouldn't want a boat on the opposite pontoon not being able to go into reverse to stop cause their engine has stalled.

Personally I only start the engines when we are ready to untie lines and always turn off when in the lock cause I'm good like that!!

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[Robin]

I did it also years ago on a Bukh 10 too, despite the manual saying open the throttle. It seemed to start easier that way, with an open throttle it took ages to wind up the revs! I think the idle speed on our Yanmar is 650rpm and yes it is 4 cylinder. If I remember right the MD2B cold start is set by opening the throttle then pressing the button so you couldn't start at tickover AND have coldstart I guess. The Bukh was direct injection as was the Mercedes the Volvo MD22L and the Yanmar, maybe that is the difference since the MD2B is indirect injection I believe (lower compression?).

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[Oldhand]

<<This also has the added advantage that it ensures that fuel is flowing and that there aren't any blockages in the fuel system>>

Where did you get that idea from? If there was no fuel flow it wouldn't start or only run for a few seconds. Even if it runs under your "warm-up" conditions this is no proof that once the load comes on, a restriction in the fuel system (clogged filter) won't prevent the increased flow required and your engine could still splutter to a stop when you open up in gear. I think you need to think about this a bit more.


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[jimi]

Can happen. If there is a slight leak in say the primary fuel filter seal, which is pre the lift pump, an air lock can hit the engine at an embarrassing moment cos all the fuel in the lines and secondary filter will keep engine running for a couple of minutes .. I know cos its happened to me.

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[bedouin]

It happens.

There is enough fuel between the primary filter and the engine to start it - problems with the fuel supply such as a blocked pipe, water in the diesel or clogged filter is most likely to show itself a few minutes after starting.

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[oldharry]

Lots of good advice here, and some not so good...!

Firstly: if a cold diesel refuses to tick over or stalls going in to gear there is a fault usually in the cold start mechanism. Nearly all engines require a slight increase in tickover revs to keep running when cold to counter reduced power output, stiffness due to cold oil etc. Some acheive this by an electrically operated device within the injector pump controlled by a sensor on the engine, others use a mechanical device linked to the coolant temprature, which opens the throttle very slightly, and several other variations.

The simple stopgap to overcome this is to marginally increase the tickover speed. a 4 cylinder diesel will normally tick over at around 800rpm against a maximum of 4-5000rpm. The cold start device will increase this to between 950rpm and 1100rpm until the engine has warmed a bit.

The warm up go from cold debate has arguments both sides. Certainly warm up for 30 minutes is a total waste of fuel, and can damage the engine by carbon build up, glazing, uneven heating etc. Good seamanship would suggest that running the engine for a few minutes to be sure it is running smoothly is prudent before casting off, and thrashing from cold is definitely to be avoided until the oil has had time to warm up and circulate efficiently.

Turbos require further attention: Never ever run a turbo engine hard on cold start - the turbo depends on its oil supply to survive, and until the oil is circulating properly can be badly damaged if revved hard when cold. Stopping depends to some degree on the make of engine and turbo. Some have an electric pump which continues to run coolant past the turbo after switch off, in which case there is no need to keep the engine running during cool down. Again, never rev a turbo diesel just before switching off. the turbo needs 5 - 10 seconds to run down from a power burst, and if the engine is switched off during that time, it will be running dry. At 100,000 - 150,000 (maybe a lot more) rpm in the turbo, that is definitely asking for trouble!

Larger commercial diesels such as ferry boats are rather different to anything we are likely to be using, and the start stop cycle considerations are very different, but smaller working boats only run their engines when needed. This saves fuel, and wear.

Small normally aspirated yacht auxiliaries simply dont need to be warmed up - they will get there soon enough, and a whole lot quicker if they are being made to work. Extended idling from cold can cause quite serious longer term problems apart from glazing. Unequal warming of the head can distort it and cause the gasket to leak or fail. Moisture in the rocker box is not warmed out efficiently, and corrosion of the valve springs can occur leading to rapid failure. Carbon will build up in the combustion chambers and exhaust, and unless the engine is subsequently thrashed hard will remain there, sapping power.

As a rule of thumb - unless the manufacturer specifically advises otherwise - don't start the engine until its needed.

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