A text by Dr Marie Schneider
There’s a well-known saying that the two best days in a boat owner’s life are the day they buy their boat and the day they sell it. If you avoid the typical mistakes when buying, there’s a good chance that the days in between will be enjoyable too.
The list of potential faults on a second-hand yacht is virtually endless, but damage to the engine, the hull and the rigging is particularly serious – and can quickly result in a total economic loss, especially with cheaper yachts. What’s more, they can quickly become a serious safety risk on the water. Here, we focus on the engine and describe non-invasive methods that can reveal signs of many obvious engine problems – and some less obvious ones.
Further interesting technical articles on engines:
The inspections described are extremely thorough. Prospective buyers and yacht surveyors rarely test engines to such an extent. Consequently, you can expect raised eyebrows from estate agents and sellers. However, this should not deter the potential buyer from carrying out a meticulous inspection of the engine.
These questions will help you learn about the history of the engine
If you’re travelling to view a car, it’s best to let the seller or estate agent know in advance that the engine shouldn’t be started before the test drive. If you place your hand on the engine, it should be cold – if it’s lukewarm, it means it’s been running recently. All too often, viewings begin with the engine already running. If the engine is already warm, this can mask compression or starting problems.
A conversation with the owner can reveal a great deal, for example regarding the engine’s performance. The hour meter alone does not provide any indication of the engine’s condition. Were the owners keen sailors who only used the engine for manoeuvring in harbour? That would be a warning sign. Coking is a particularly common problem on sailing yachts. This involves sludgy deposits throughout the engine, which occur especially when the engine has not been properly warmed up and has only been used at low revs.
Clarify the installation situation and background
Did the owner carry out the maintenance themselves or commission a specialist workshop? Unfortunately, neither option is a guarantee of good upkeep. Old invoices can provide an insight into the scope and frequency of maintenance. If the owner carried out the maintenance themselves, ideally you’ll be shown a detailed maintenance logbook. Was it just a case of changing the oil and filters, or was the internal cooling circuit flushed from time to time? It’s hard to imagine, but many owners believe they carry out maintenance very conscientiously, yet don’t even realise that their engine contains sacrificial anodes which need to be replaced or, depending on the sailing area, changed. Where maintenance has been carried out at a shipyard, it may be that only the work commissioned was carried out, and not the work required by the manufacturer for the specific engine model. So: in any case, obtain all available information on maintenance and operating habits. This can be done before opening the engine compartment.
The visual inspection in the engine compartment raises further questions
The engine and the area around it should be clean. If the engine is dirty, it is likely that maintenance has not been carried out with the necessary care. The absence of a detailed maintenance log is even stronger evidence of this.
If the engine bilge looks as though it has just been cleaned, it may be that an oil spill was wiped up just a few minutes before the viewing. So a bit of dirt in the bilge is nothing to worry about.
Next, the engine is inspected all round: is it even possible to service the individual components? For example, can the heat exchanger’s tube bundle be removed, or is there a bulkhead in the way? If so, this has probably not been done. Painted screws with no cracks in the paintwork are also an indication that they have never been opened and that the components underneath have therefore not been serviced.
Visual inspection I
You should also look out for signs of salt water leaks. Corrosion on the end caps of heat exchangers or intercoolers with aluminium housings, in particular, may necessitate a costly replacement. The exhaust manifold is often the source of leaks. If it has rusted through, the only solution is to replace it. In this case, the cost of the spare part and the accessibility of the engine compartment both determine the extent of the repair work required.
Oil leaks need to be assessed on a case-by-case basis. A bit of oil on the cylinder head cover of an older engine? That’s almost to be expected and easy to fix. Is oil dripping from the flywheel housing through the crankshaft oil seal? The spare part costs next to nothing, but the labour involved is enormous.
It is also important to check the condition and levels of coolant and oil in the engine and gearbox. Unfortunately, the latter in particular is often neglected. Milky oil and cloudy coolant are signs that the two have mixed. This may be caused by a faulty cylinder head gasket, which is a complex repair and therefore an expensive fault to fix.
These components are often overlooked during the check
Belts and pulleys also need attention. If there is a lot of belt dust, this may be due to an alignment problem that cannot be resolved simply by replacing the belt.
A wiring harness damaged by a DIY-enthusiast owner or by cables that have become brittle due to diesel leaks, a tattered air filter, or engine mounts that have become soft or brittle? These are signs of a lack of maintenance.
Visual inspection II
But it’s not just the engine that needs to be in working order and correctly fitted; everything around it must be too. This applies to the entire drivetrain, the electrical system on the control panel, Bowden cables, the diesel pre-filter and the diesel tank. How old is the Saildrive seal? When were the shaft seal and stern bearing last replaced? Are any hoses brittle or hose clamps corroded? Are there any signs of diesel sludge? Certain types of damage can be detected indirectly. For example, if there is a small lump of wax under the stuffing box, it has been tightened too much. This will cause the shaft to seize up. That will be expensive.
If the throttle and gear lever feel stiff or catch, the Bowden cables will probably need replacing. Dark deposits in the sight glass of the pre-filter (which we hope is fitted!) indicate microbial breakdown products and asphaltenes; a full-blown diesel contamination in the tank is then likely. If the filters have only recently been changed, you should check the sight glass again after the test drive.
A cold start says a lot about the condition of the engine
Following this thorough visual inspection, white oil-absorbent mats are placed in the engine bilge and left there until the end of the test run. We then start the engine.
It is usually only on multihull vessels that there are two engines. By testing them separately, it is possible to clearly identify the source of any smoke or noise.
A diesel engine should start within one to two seconds – following correct pre-heating, provided it has glow plugs. Any delay indicates a problem. As soon as the engine is running, go to the rear and check the exhaust fumes: In older engines with mechanical fuel injection, a light blue or black wisp of smoke in the first few seconds is normal, but it should disappear quickly. In common-rail engines – i.e. those with electronically controlled fuel injection – any smoke is a warning sign.
Engine checks whilst the engine is running during a test drive
Now cast off and test the engine whilst underway. Whilst the owner manoeuvres the boat out of the harbour, take another look (wearing ear protection) in the engine compartment. Unusual vibrations or rattling noises can have a variety of causes. It may not even be the engine itself that’s the culprit, but perhaps the alternator bearings, for example. You should also use your sense of smell: diesel, burnt oil, rubber, overheated cables, coolant or sulphuric acid from batteries – each has its own distinct odour. You wouldn’t want to find any of these in the engine compartment.
You should now ask the owner to switch from forward motion at around 1,000 revolutions per minute to neutral and then immediately into reverse. The engine must not cut out. If it does, however, this may be due to the propeller size or the drivetrain. Whilst travelling in reverse at around 1,500 revolutions per minute, observe the engine mounts: they should move only minimally, just as they do when travelling forwards.
Don’t be afraid to put your foot down – the engine has to be up to the job
After 10 to 15 minutes, the engine has typically reached its operating temperature. The clutch is then disengaged and the engine revved up to full throttle. The engine should reach a speed of 50 to 100 revolutions per minute above its rated speed. Values significantly above or below this indicate a problem. Now engage the clutch again. Every five minutes, increase the revs by 500 revolutions per minute until you reach 10 per cent below the rated speed. Continue driving like this for 30 minutes to allow the engine to warm up properly. Finally, run the engine at full throttle for ten minutes – push the throttle lever right to the floor! Full throttle may seem like a lot, and the sensation of the engine ‘sucking in’ on displacement engines is very unfamiliar. However, the subsequent tests are necessary to assess the condition of the engine.
Put your foot down – but do it properly
Concerns about damage caused by the test are unfounded. All diesel engines, including recreational engines, are designed to run regularly at full throttle (for recreational diesel engines, this amounts to around one hour in every eight, but at least 30 minutes every 10 hours). If the engine – and, above all, its cooling system – cannot cope with 10 to 20 minutes at full load, something is wrong. In that case, the problem was already present beforehand and is not a consequence of the test.
Experience shows, however, that carrying out tests of this sort rarely goes down well with estate agents and owners, even though diesel engines can easily cope with them. But when it comes to undetected damage, it’s your own money at stake, so you should politely insist on it.
Check that the machine is working properly at full throttle.
First question: Does the engine even reach its rated speed? If not, it may be overloaded (propeller too large) or there may be another problem. Second question: Is the engine overheating? The cooling system is designed to cool the engine sufficiently at full throttle – even in warm Caribbean waters. If the engine overheats during testing, this could be caused, for example, by a limescale-clogged heat exchanger. This brings us back to the initial questions: When was the coolant last changed, and has the tube bundle ever been descaled? The temperature analysis could be taken a step further using an infrared thermometer: at the oil sump, we would expect a reading of just over 100 degrees Celsius, and around 70 degrees at the wet exhaust. The temperature differences between the cylinders should not exceed 10 degrees. And a standard gland should not exceed 60 degrees.
Third question: Is the engine getting enough air? If you feel a draught when you open the bonnet, or if the revs suddenly increase, the engine compartment is too airtight and the engine is not getting enough fresh air. This is not an engine problem, but an installation issue.
Fourth question: What about cylinder wear? A compression test is invasive and is rightly rejected by most sellers. A test that isn’t perfect but is helpful: check the crankcase ventilation for blow-by at full throttle. If the engine has a sealed vent, you can pull the dipstick out slightly or open the oil filler cap. A slight flow of air is normal; a strong flow of air is a reason to carry out a proper compression test.
Back at the jetty, the final inspection takes place. Are there any leaks visible on the oil-absorbent mats laid out earlier? Professional oil and coolant analyses are most useful when carried out as a time series. As a snapshot, they can at best indicate contaminants (such as diesel in the oil) and significantly excessive signs of wear. Now would be the time to take a sample.
How an engine test influences the decision to buy
Once the engine has been inspected, you’ll have a wealth of information – and no doubt still some unanswered questions. Is the oil leak you’ve found simply a harmless sign of ageing, or will the engine need to be overhauled at a cost of thousands of euros? To answer such questions, you should now obtain quotes for the repair. The cost of the same repair can vary between different engine models, depending on the availability of spare parts. If spare parts are no longer available, a replacement engine is sometimes required.
At this point, many people start to have second thoughts about buying the boat. But what condition is the rest of the yacht in? Can you get it for such a low price, and is the overall condition good enough to make the purchase worthwhile after all? Another important factor to consider is how technically savvy you are as an owner, and whether you have enough time and inclination to carry out certain tasks yourself in order to save money. In that case, an engine that requires a lot of maintenance is less of a problem than if you have to rely on a shipyard for every job. Maintenance and repair costs can quickly add up to the cost of a replacement engine.
Things to avoid: When an engine has definitely suffered costly damage
Significant corrosion or dirt, poor cold starts, blue smoke, an oil film on the water, water in the engine or gearbox oil, and gear-changing problems that are not related to the Bowden cable are all reasons why you should only proceed with the purchase of the boat under significantly different conditions – or not at all.
Of course, there are problems that may go undetected by the engine test described here. However, if the engine looks clean and well-maintained, detailed service records are available, the cold start is satisfactorily quick and without any significant smoke, and the engine runs well even at full throttle without overheating, then it is highly likely that it is in good condition.
When to seek professional help from a mechanic
If the engine is large and expensive (from around 150 PS), it is worth investing in a professional engine assessment. The vast majority of vehicle surveyors only offer a functional test (forward, reverse, and a brief burst at full throttle). For an engine inspection, you should look for a specialist who offers additional tests, such as removing the fuel injectors to carry out a compression test.
Even further tests do not provide complete certainty
The tests described are very comprehensive. The findings may influence the decision to buy or the price of a second-hand yacht. But the truth is: even so, they only provide a guide, and even an in-depth engine survey involving, for example, a compression test, does not provide 100 per cent certainty.
The significance of the hour counter
It is often said that diesel engines can easily run for 4,000 hours before they require their first major overhaul. Unfortunately, this is too general a statement – the hour meter is only meaningful if you know how the engine has been used. When operated correctly, engines can run for as long as 8,000 hours without an overhaul. A serious problem with leisure boats, particularly sailing yachts, is operating at too low a revs and with the engine running too cold. To prevent carbon build-up, diesel engines must be run hot and at a sufficiently high revs. Ten minutes of operation at 1,000 revolutions per minute whilst mooring and casting off will send a diesel engine to an early grave.
Buying a yacht on land
It is possible to carry out a cold start on land. To do this, the impeller is removed (it must not be allowed to run dry) and the engine is then started. It can run for a short while without cooling, allowing you to check that it is functioning correctly. If the engine has been winterised beforehand, any antifreeze in the exhaust system must be collected to prevent it from entering the environment. This is not particularly practical, and all other engine checks that form part of a test run cannot be carried out on land. It is therefore better to take the boat out on the water for the engine check.
Dr Marie Schneider on the BoatHowTo.de boat diesel course
Who is actually behind BoatHowTo.de?
Nigel Calder and Dr Jan Athenstädt developed the engine course, which was originally in English; I have adapted and expanded it for German-speaking countries. Thanks to my work – previously as a yacht broker and now as a boat-buying adviser – I am familiar with the concerns of first-time owners and the typical pitfalls.
Can boat owners manage at all without any knowledge of the engine?
To a certain extent. I’m constantly coming across customers for whom the engine is a black box (“Best not to touch it at all!”). As long as they have the financial means, a specialist workshop is within easy reach and has available slots, this doesn’t have to be a problem. But I always tell them: the engine is one of your most important crew members and needs the same attention as the rest of the crew and yourself. My aim is to reduce people’s fear of getting their hands dirty and to get them out on the water safely and with confidence.
Does the course only cover maintenance work?
Not at all. The course starts from scratch so that all participants are brought up to the same level of knowledge. Over the course of more than 100 lessons, we not only demonstrate the maintenance of all components, but also explain how diesel engines work and cover troubleshooting. Through a combination of workshop sessions and theory lectures featuring animations, we go into great depth, so that even professionals can learn something new. This also applies to the powertrain, fuel tank and filter installation, and the exhaust system.
Which diesel engines is the course suitable for?
We demonstrate maintenance work on a wide range of different models. All makes, models and engine sizes operate on the same principle. Whether with or without a turbocharger, whether shaft or Saildrive, whether mechanical or modern with an electronic control unit. So even if you’re still in the process of buying a boat and aren’t yet an owner, you can still benefit from the course and apply the knowledge to your future engine.
When does professional help become essential?
If the owner has the will, the necessary tools and the workshop manual, a specialist workshop is only called upon at a later stage – for example, when the machine requires a major overhaul or when dealing with highly complex or high-precision components.
The online course
Good maintenance and driving habits are essential for a reliable engine. The online course on marine diesel engines from BoatHowTo.de offers a comprehensive solution for boat owners who want to understand their engines better and carry out their own maintenance. The package includes over 10 hours of video content across more than 100 clearly structured lessons on how engines work, maintenance, troubleshooting and repairs. Price: 299 euros
