Engine Maintenance: WOBBLE and Schedule

Exhaust, silencer and the rear of an engine.
Exhaust, silencer and the rear of an engine.

It is an excellent safety measure to check the engine and its auxiliary systems prior to its start. I do not pretend to be the author of most of the information below, but it was thaught to me on various occasions (and the authors are pointed out when needed). I discuss the acronym WOBBLES, discuss of a maintenance schedule and of the importance of engine power curves for fuel consumption planning.

  • Water intake examination.
  • Oil levels and appearance.
  • Battery’s state of charge and connectedness.
  • Belt’s tension.
  • Leaks or hopefully lack thereof.
  • Exhaust pushing water once started.
  • Sound of the engine once it has started.

Checking the water supply involves examining the water intake seacock, which should be open before starting, and the strainer, which should be 1) present and 2) clean.

The oil check involves checking the transmission oil (usually measured close to the shaft coupling) and the engine oil (at the front for Beta Marines, on the side for Yanmar, varying for Volvo). Of course, you need a sufficient quantity of oil (10W40 in the south). The oil level should also be checked after use, to get a better reading. At rest, the oil falls back into the oil sump. Attention should also be paid to its color and consistency (details below).

The belt check should include an assessment of its tension (“one centimetre with your thumb”), the condition of its teeth and general fatigue.

Batteries should be checked for proper connection to the starter (circuit breaker), charge level and (less frequently) cable condition.

Checking for leaks involves inspecting the shims, the underside of the engine and the most likely leak points, i.e. the joints between metal and rubber (diesel inlet, water mixing elbow), filters, bleed points and the impeller cover on the water pump. Oxidation, diesel smell or the presence of oil is a sign of leakage.

Checking the exhaust usually boils down to examining the water outlet and the smoke that may be coming out of it. The color of the smoke indicates problems and possible causes (detailed below). You can also check the condition of the anti-backflow elbow and the rubber manifold.

Noise is also an indication of engine condition: at start-up, the engine is still cold and its noise should be more “square”. As it warms up, however, it should become rounder. Signs of squealing indicate a worn belt, or one that lacks tension. A sign of metal hitting metal is a sign of a major problem (piston or transmission) and the engine should be stopped.

And I Would Add

It is a good idea to be aware of the technology you will be using, especially if it is not your boat. Where is the manual stop button (on the engine)? Is the transmission lever different from the gear lever? Which direction is forward/reverse? Can you feel “neutral”? Which direction is the propeller pitch?

If it is accessible and you are using it for the first time, an examination of the “bottom” of the diesel tank is a good idea (presence of “mud”, etc.).

Finally, before starting up, noting the engine hours and tank level (if the gauges are working!). Repetition gives the best data on engine consumption.

Common Symptoms

What to do in those situations? Taken from Casey (2006):

SymptomLikely Cause(s)
The engine does not turn upon starting up.Electrical problem, engine seized.
The engine turns, but does not start.Water in diesel, blocked injectors, compression leak.
The engine starts but has an « hiccup »Obstructions in the air and/or diesel intakes.
Black smoke.Incomplete combustion. Lack of air.
Whit smoke.Incomplete combustion. Lack of diesel.
Blue smoke.Burned oil.
White/Mayo oil.Water/Cooler in the oil sump.
Engine overheating.Water intake blocked, lack of oil, exhaust blocked.
Low revs.Lack of air, injector problems, piston stuck.
The engine vibrates more than usual.Rope around the propeller, bent shaft, fasteners unscrewed.
Source: Casey (2006).

There are other causes. Have a look at Casey (2006) for further cases.

Maintenance Schedule

It is hard to do better than Calder (2007):

TaskFrequency
Diesel fuel line inspectionSeasonally
Check for corrosion.daily
Check for oil leaks.daily
Check oil levels.daily
Check the engine cooling level.daily
Check the water strainer.daily
Check the first diesel filter.daily
Check the pressure generated by the pistons.after 50h
Changer the oil.after 50h, then every 125h
Change oil filter.after 50h, then every 125h
Check batteries fluids (if lead-acid).after 50h, then every 125h
Check transmission levels.after 50h, then every 125h
Change the first diesel filter.every 125h
Check valve closing tolerance.every 250h
Check engine alignment.every 250h
Change the cooling liquid.every 250h
Check the rotor.every 250h
Check the cooling system.every 250h
Changing the second diesel filter.every 250h
Changing the air filter (paper).every 250h
Changing the air filter (metal).every 250h
Testing injectors.every 1000h

Consumption Curves

It is very useful to familiarize yourself with the consumption curves of an engine. It is much more informative than rough rules of thumb. I have never seen an engine model where these curves were not communicated in their technical manual. Below, I illustrate a curve for a Beta Marine 20 (I have also illustrated a curve for a volvo penta 57).

In the image above, diesel consumption corresponds to the bottom curve. It is expressed in liters per hour. The curve is increasing and convex, a feature common to all diesel engines. This means that the increase in diesel consumption is more than proportional to the increase in speed. In other words, the faster you want to go, the more fuel it’s going to cost. Conversely, the slower we go, the further we’ll be able to go with the same fuel reserve.

By way of illustration, the Beta 20 consumes just over 4 liters per hour when running at 3600 RPM. However, at 2200 RPM, it consumes just 1 liter per hour. If a boat goes at 7 knots at 3600 RPM, goes at 5 knots at 2200 RPM and has an effective fuel tank of 100 liters, then it has a range of 175 MN at 7 knots. On the other hand, it has a range of 500 MN at 5 knots, i.e. almost three times as far! Cruising speed is an important factor in determining actual motor range.

References

Beta Marine USA (2022). Beta 20 Data Sheet, retrieved online in november 2023 at https://betamarineusa.com/portfolio/beta-20/.

Calder, N. (2007). Marine Diesel Engines: Maintenance, Troubleshooting and Repair, McGrawHill, ISBN 978-0-07-147535-6, 294 pages.

Casey, D. (2006). Marine Diesel Engines: Maintenance, Troubleshooting and Repair, McGrawHill, ISBN 978-0-07-146284-8, 881 pages.