Reading her — The routine, the smoke and the fault
Reading notes · The diesel engine
The two-minute routine before you leave, what the colour of the smoke sends you to, how a symptom becomes a short list in the right order, what you carry, and what the examiner asks with the compartment open.
Open the interactive chapter →The same material with the chart, the drawings and the exercises.
Reading her · The routine, the smoke and the fault
Six letters, before you turn the key
Everything in this course so far has been about one part at a time. This is the routine that touches all of them, and it takes about two minutes.
W · Water. The raw-water strainer, seen through its lid. Weed or plastic in the basket and you deal with it now, not when she is running hot in a channel.
O · Oil. The dipstick, cold and on level trim. Between the marks. And the colour of it: amber is right, milky means water, and a level that has gone up on its own means diesel.
B · Belt. Press it. About right, no cracks, no glaze, no black dust. One belt, three jobs.
B · Bilges. Look under the engine. It should be dry. Water, oil or diesel down there is the first thing that tells you about a leak, and it tells you for free.
L · Levels. The coolant in the header tank — cold — and the gearbox oil. Two levels that are not the engine oil and get forgotten because of it.
E · Exhaust. Start her, and look over the stern for water. That one is the next screen.
Nothing in that list is hard and nothing in it takes long. What makes it work is that it is always the same six, always in the same order, and always before you leave — so you do not have to remember what to check, only to check.
Every single one of those six has caught a real problem on a real boat before it became an expensive one. That is the whole argument for it.
The first thirty seconds
The last letter of the six is the only one you do with the engine running, and it is the reason the other five are worth doing.
You have checked five things with the engine cold. Now you start her, and within the first few seconds water should be spitting out of the exhaust with the gases.
That one look confirms the whole seawater circuit at once, and it is worth listing what it proves.
The seacock is open, or no water would be coming in. The strainer is clear, or not enough would get past it. The impeller is turning and in one piece, or nothing would be pushing it. The belt is on and tight, because that belt is what turns the pump. And nothing downstream is blocked, because the water got all the way through and out.
Five things, one look — and it does it right after you have checked, by hand and cold, the four that would have caused it.
So the six are not six separate checks. They are one check with five preparations.
And if there is no water: stop her. Now. You have just done the routine, so you already know the strainer was clear and the belt was on — which means it is the seacock or the impeller, and one of those two is free to check. Look at the seacock first: it is the one somebody closed.
It is one of the two checks in this module where the right answer is to act before you understand — the other is the oil-pressure alarm — and after the routine you are two seconds from understanding anyway.
Blue, black, white
A diesel exhaust that is working is almost invisible. When it is not invisible, the colour tells you which system has the problem — and the three that tell you anything are blue, black and white.
Blue is oil. The engine is burning its own lubricating oil, and oil is getting into the combustion chamber where it does not belong. Worn piston rings let it up past the piston; worn valve guides let it down from the head. It is the smoke of an old engine and it comes on slowly. You confirm it by the level on the dipstick going down with no leak anywhere — nothing is dripping, because it is going out of the back of the boat.
Black is fuel that has not burned properly. Too much fuel for the air available, or fuel arriving badly, and either way it is unburned carbon coming out. So there are two sides to look at, and one of them is nearly free. Not enough air: a choked air filter, or a turbocharger that is not delivering. Bad injection: worn or dirty injectors putting the diesel in as drops instead of mist.
Start with the air filter every time. It is the cheapest thing on the list and the commonest cause, and it takes a minute to look at. Injectors are workshop work, and you go there only after the air side is clean. Black under load is the one to notice: a puff when you open the throttle hard is normal on an older engine; black that stays while she works is not.
White is water — and white is the one that ends the passage. Coolant is getting into a cylinder and going out with the exhaust as steam, and the joint that lets it do that is the head gasket.
You confirm it with two things you already know how to check. The coolant in the header tank goes down with nothing leaking outside. And the oil may go milky — may, because a gasket can fail into a cylinder without touching the oil galleries at all.
A cold engine on a cold morning puffs white for a minute and then clears. That is condensation and it is normal. White that does not clear once she is warm is not.
Blue sends you to the rings and the valve guides. Black sends you to the air filter first and the injection second. White sends you to the head gasket, and the header tank confirms it. And you will be asked.
Where the smoke sends you
Three colours, three systems, and each one sends you to a different part of the engine you built.
Blue sends you inside the cylinder — to the pistons and their rings, and to the valve guides in the head. Nothing you can reach, and nothing you fix at sea. What blue buys you is knowing, and knowing means watching the oil level and planning a rebuild rather than being surprised by one.
Black sends you to the air first and the fuel second, and that order matters because one end of it is free. Air filter, turbocharger, then injectors.
White sends you to the top of the engine — the head gasket, the joint you learned about in the very first phase — and it sends you to the header tank to confirm it before you decide.
And two things the colour does not tell you. It does not tell you how bad it is. A trace of blue on an old engine that is otherwise fine is information, not an emergency. White that does not clear is an emergency, and the same colour on a cold morning for thirty seconds is nothing at all.
And it does not tell you what to do next — the rest of this course does. Blue means watch the level. Black means look at the filter you can reach in a minute. White means stop, check the header tank, and think hard about whether to go on.
The colour is the question. Everything else you have learned is the answer.
From a symptom to a part
Nothing on this engine tells you what is wrong. It tells you what it is doing, and you work backwards.
That is the whole skill, and you already have every piece of it. Eight phases of knowing what each part does, and a set of symptoms that each point at two or three parts rather than one.
A symptom rarely has one answer, and that is not a weakness. No water at the exhaust does not mean «the impeller». It means the seacock, the strainer or the impeller — three parts, in that order, from free to awkward.
A good diagnosis is a short list in the right order, not a single guess. The person who says «impeller» and takes the pump apart while the seacock is shut has not diagnosed anything; they have been lucky or unlucky.
Free first, then cheap, then awkward. It is the rule that makes the list an order instead of a pile. Looking at a seacock costs nothing. Looking through a strainer lid costs nothing. Pressing a belt costs nothing. Do all of those before you undo one screw, because half the time you will be finished.
And before any of it: the boat is still moving, or it is not. An engine that has stopped is a problem you can take an hour over; a boat drifting onto a lee shore is not. So before you open anything: get sea room, or get an anchor down, or put somebody on deck who is steering and looking. Then fix it, and take as long as you like.
What you carry
A spare you do not have is a part that has failed permanently.
That is the whole of it. On a boat there is no shop, and the difference between a delay and a passage ruined is usually a small box in a locker.
The one everybody agrees about: a raw-water impeller. It is the first spare on the RYA's list and on everybody else's, because it is the part most likely to fail, it fails suddenly, it fails at the worst moment, and it is a rubber lump the size of a golf ball. Carry it, and carry the gasket for the cover with it.
Two full sets of fuel filters, not one — because the reason you are changing them is usually dirt, and dirt does not stop after one set. A drive belt, with the wrenches that fit the alternator. A thermostat, which is small and cheap and stops the engine dead when it sticks. Anodes, for the heat exchanger and the shaft. Oil, an oil filter, and gearbox oil. Hose and hose clips. Fuses, terminals and cable.
And two that are not engine parts at all: tapered wooden bungs, and the engine's own manual.
The obvious tools — wrenches, screwdrivers, pliers, a knife — plus the ones that are specific to this job and get forgotten: an oil filter wrench, an oil extraction pump, absorbent pads, a wire brush and petroleum jelly for terminals, a torch with spare batteries, a multimeter, and gasket paper.
Keep them together, keep them in the engine locker, and know they are there. A tool somewhere else on the boat is a tool you will not fetch at two in the morning.
What you do, and when
Everything on this engine either gets checked on a rhythm or gets found out about at sea.
Before every trip · the six letters. That is the WOBBLE, and it is the whole of what you do before you leave. Two minutes.
Monthly, or thereabouts. Drain the water separator bowl. Look at the stern gland and give the greaser a turn. Check the battery terminals, and the electrolyte if they are the kind you can open.
Annually · the full service. Engine oil and its filter. Both fuel filters. The gearbox oil. Anodes. Coolant strength. Every electrical connection cleaned and remade. And the impeller — changed even if it looks perfect, because rubber hardens with age and not just with use.
Once a season is what most people do, and that is a habit rather than a figure. Your engine's book gives the interval that counts, and it is the one to follow. What is not in dispute is that you do not wait for it to fail: it fails suddenly and it takes the cooling with it.
Every two or three years. Have the starter motor serviced, and have the injectors tested. Neither is a job you can do, and neither can be judged from outside — which is exactly why they go on a clock instead of on a symptom.
And laying her up, which is a service of its own. Change the oil immediately before winter, not after it. Used oil is acidic, and leaving it to sit in the engine for six months eats bearings while the boat is on the hard doing nothing. Then run her to circulate the clean oil.
Fill the fuel tank. A full tank has no room for the air that condenses into the water that feeds diesel bug. And if you are prone to bug, this is when the biocide goes in — you have a whole winter for it to work.
Flush and drain the seawater circuit, take the impeller out and store it flat, so it does not set in the shape of its housing. Close the seacocks. Check the antifreeze strength. Grease the stern tube. Batteries fully charged and kept that way. Seal the exhaust and the air intake against damp and things that nest.
And leave a note of what you have done, because in April you will not remember, and the impeller you took out is not in the engine.
Read the symptom
Fourteen symptoms, one at a time. Each one has more than one honest answer — so the question is not what could be wrong. It is what you look at first.
Free before cheap, cheap before awkward.
The compartment is open
This is what it looks like.
The boards are up, the engine is there, and somebody is going to point at things and ask you what they are. Then they are going to ask you what the smoke means, and how you would change a filter, and how you would bleed it, and what you would do if no water came out of the exhaust.
You have done all of it. Eight phases of what the parts are and what each one does. Eleven jobs done with your hands, in order, with the reason for every step. The three colours and where each one sends you. A symptom, and the short list in the right order that it points to.
And none of it was memorised. You built the engine one piece at a time and every piece arrived because the one before it needed it — which is why, standing in front of a real one with the boards up, the questions are about something you have already seen.
One last question, and it is the one you will actually be asked.
Open the interactive chapter →The same material with the chart, the drawings and the exercises.