How to check a diesel when buying a used yacht without starting it
Denis Korablev
  • 05.08.2020
  • 129

How to check a diesel when buying a used yacht without starting it

When purchasing a used yacht with a diesel engine, the problem of checking it arises. The fact is that the owner who "knows" the engine can distort the current problems so strongly that it will inadvertently mislead even an experienced specialist. At the same time, it is possible to check the motor quite accurately even without disassembling it. Below we give tips with which you can independently give a fair assessment of the condition of a diesel engine.


Dirt is an important consideration when checking an engine, and there is no doubt that cleanliness is an indicator of how much the previous owner cared about it. Even visually assessing the appearance of the owner, one can draw some conclusions about his attitude to technology. Keeping the engine clean requires serious work from the owner, regular inspection and cleaning, not just washing problem areas with detergents that do not remove stubborn dirt.

It will be very good to have a maintenance log attached to the clean external condition of the engine. These records, at a minimum, should reflect all cases of oil and oil filter changes, fuel filter changes and other types of work with reference to the engine hours at which they were performed. In the absence of a motorcycle hour meter on the motor, it may well be that the maintenance was not carried out on schedule.

In support of the records, you can ask the owner of the yacht for an oral report. Reports can indicate a lot, for example - if the owner says that the fuel filters were changed even more often than the instructions require (due to the fact that they quickly clogged up), it is worth asking the question - how clean the fuel was fueled by the ship ?


The issue of diesel fuel purity deserves no less attention. Fuel system elements are the most expensive of all engine components. Any problems with the fuel system can result in serious financial problems. Since low-quality fuel is one of the main causes of engine failure, the fuel system should be checked for proper maintenance and cleanliness during the operation of the vessel. The simplest check on the fuel system is to pump some fuel out of the tank near the bottom and let it settle in a transparent can.

If, after settling, a dirty sediment appears at the bottom of the can, the state of the entire system can be put under suspicion. Diesel engines use two types of filters - coarse and fine. If there is no coarse filter, then you should not particularly trust the owner about the "good" or "ideal" state of the motor. To check the filters, you need to disassemble and pay special attention to the fine filter - if it is heavily soiled, the engine is almost certainly worn out.


While the condition of the lubricating oil is undoubtedly a concern for the buyer, visual inspection does little in fact. Since soot and metal particles are a common product that is constantly released when the engine is running, they still change the color of the oil, as a result, even the recently replaced oil becomes black. Therefore, black should not cause you unnecessary anxiety. However, it is worth to evaluate the viscosity of the oil by taking it from the tip of the dipstick and applying it to your fingertips. If the oil is changed often enough, the oil stain on the fingers will spread and look lighter and more transparent around the edges. And if the oil was rarely changed, it will be immediately visible by its intense black color, and it will spread much worse.

As noted by the specialists 2yachts, an irregular oil change can also be signaled by black sediment on the inner surface of the filler cap. The creamy color of the oil indicates the presence of water in it, which indicates a leakage of the cooling system or its condensation (water is a natural product of the combustion process). Water in oil is a bad sign.

If moisture enters the cooling system, most likely this occurs through places where the integrity of the gasket of the head of the block has been damaged or through corrosive holes formed in the cooling jacket. Moisture can also come with antifreeze, which reacts with oil and forms a difficult-to-remove film on the parts of the cylinder-piston group.

These available methods of oil testing are very useful to continue with spectral analysis of a oil sample under laboratory conditions. But it is not so easy to interpret the results of the study correctly if there is no information about the number of engine hours worked by the engine with new oil. A fairly objective picture of the state of the oil can be obtained by taking a sample for analysis from about the middle of the level with a warm engine.

Engine cooling system

In diesel engines with a dual-circuit cooling system, the fresh water (or antifreeze) circuit rarely creates significant problems. And a completely different matter is the seawater circuit, since hot salt water and various types of metals enter into chemical interaction here. And despite the protection of heat exchangers with special zinc protectors (anodes), this part of the system still often suffers from corrosion. Heat exchangers are very expensive, so be sure to inspect them to ensure that the zinc anode is intact and correctly installed. This can be done by shutting off the seawater supply valve and unscrewing the bolt with the protector. The destruction of the anode should not be more than half, if the anode is simply absent (has undergone complete dissolution), then the performance of the heat exchanger is called into question.

You can also visually assess the cooling system, with the most accurate indicator being the seawater inlet on the refrigerator - you will need to remove the seawater supply hose and inspect the inlet. As a rule, when exposed to corrosion, this place is subject to destruction faster than all other parts.

Rubber elements

When inspecting the heat exchanger, pay attention to the quality of the rubber tubes - check them for cracks or swelling, crimp the hoses by hand to make sure they are elastic. Check that the clamps are securely tightened. If you find traces of corrosion on the surface of the clamp, move it aside and inspect the surface of the rubber tube under it for damage.

It is also necessary to disconnect the exhaust pipe from the exhaust manifold and check its inner surface - it should not have a too thick layer of carbon deposits, otherwise you should expect coking of valves and piston rings. As a result of constant leaks, the support rubber cushions in the engine mount will soften, the insulation on the wires will collapse and the belts will become unusable, which will entail significant costs for replacing these components.

Finally, it is worth check the propeller shaft seal. Any traces of leaks may indicate insufficient engine care or improper diesel alignment (which is much worse). If a leak is found here, you can try to eliminate it by simply tightening the gland, and if this fails, then these attempts should be abandoned.

After the survey, the engine can be started, cold start can tell a lot about its condition, for example, about the wear of needle bearings, piston rings, etc.

If you are interested in yacht rental in one of your chosen regions - 2yachts is ready to offer you options from direct owners, just contact our specialists to get comprehensive support at all stages of the transaction. We wish you a successful holiday!