It’s not magic…Larry Rumbol takes a closer look at the additives that keep the engine room and cogs turning
With over 49 years of experience in the marine industry, Larry’s extensive career has seen him author countless
articles, participate in numerous panels, and speak at industry leading conferences. Most recently, he hosted and moderated the Superyacht Technology Show in Barcelona and will reprise his role in 2026. A two- time recipient of industry awards for his pioneering work in condition monitoring technology, Larry is deeply passionate about advancing the field and promoting its future.
As the chair of the IMarEST Special Interest Group for Superyachts, he actively fosters innovation and collaboration within the industry as well as encouraging young talent to enter the superyacht sector.
He is currently mentoring the next generation of industry professionals, sharing his knowledge and enthusiasm for the field.
ADDITIVES & POTIONS
Additives – not magic potions but as secretly guarded as any witches brew that turns living things into stone, without them the living thing that is your engine would be stone silent too.
So what are they and why are they so talked about? Let us begin with base oil as our starting ingredient. Additives are what makes each oil different. Each will have different (or similar) claims on performance and rightly so as the additives are what makes the oil fit for purpose.
It is important to understand what they do and what might happen if they are not there anymore. Additives can indeed deplete by doing their job and get stripped out by incorrect filtration. In no particular order:
DETERGENTS
Detergent additives are there to hold acid neutralising compounds in solution in the oil. They are most often alkaline and react with the strong acids that are produced during the combustion of fuel – especially if the sulphur content is higher. These sulphuric and nitric acids can cause critical corrosion to engine internals if left unchecked. Anti-corrosion, anti-wear and even extreme pressure properties can be achieved in an oil through the use of what are called ‘neutral detergents’ too.
DISPERSANTS
Dispersancy is a vital quality for an oil to have. Combustion products need to be kept in suspension in an oil and this additive prevents sludge or lacquer from forming. However, this additive will become depleted over time and is one reason that oil changes are required after a period of time and / or in accordance with a laboratory report after sampling.
ANTI-OXIDANTS
Oils naturally age or more correctly oxidise in the presence of air and an anti-oxidant inhibits this decomposition. Lubricant oxidation gives rise to the formation of lacquers, gums and sludge which increase the viscosity and acidity of the oil. A laboratory report will identify when these acidity and / or viscosity limits have been exceeded and that the oil should be changed.
There is an oil additive called ZDDP which works at temperatures above 100°C and causes many undue concerns with yachts that transit from the US/Caribbean to the Mediterranean. Some oils, which are said to be the same, made by the same company but with differing brand names, are different in one particular capacity, in that they have a greater ZDDP content. This increase (as a fresh oil charge) causes a reaction in copper components in engines leading them to microscopically shed copper, causing the said ‘undue’ alarm when a copper ‘spike’ is identified in the laboratory analysis report.
It is often thought to be the first indication of a bearing wipe. Yet without zinc or tin also spiking we can discount this, especially if a fresh charge of oil from the opposite side of the Atlantic is known. We can identify this as the ZDDP syndrome and the copper spike should slowly decline (within 100hrs normally) as the copper passivates. ZDDP’s role is to form a chemical bond between two metal mating surfaces forming a film which have lower shear strength than the parent metal.
EP ADDITIVES
Similar to ZDDP Extreme Pressure (EP) additives work in a similar manner. They bind with exposed metal surfaces to form low rupture strength films that limit damage from micro-seizure (more common than one thinks) if the oil film ruptures. In the past we could rely on a higher sulphur content to provide lubricity assistance in the same way, particularly in fuel injection equipment where lubricity in the fuel was a vital element. Today and in an increasing way with the addition of bio-fuel to distillate this lubricity, depletion is a concern.
POUR-POINT ADDITIVE
This additive is in fact a depressant to stop fuel from thickening (increase in viscosity) in low temperature situations where the waxes in mineral oils, especially less refined examples, crystalise at low temperatures. Pour-point depressants prevent this rapid increase in viscosity by preventing agglomeration of the initial wax crystals that can form.
ANTI-FOAM ADDITIVES
If you ‘whip up’ nearly any liquid, air entrapment occurs and the resulting foam can cause oil starvation and film reduction at the contacting surfaces, which can lead to the aforementioned micro seizures, or worse still major seizures. Gearboxes are a prime example due to the high speed and load of the internal components.
POLYMER THICKENERS
Multigrade oil is a well-known phrase in today’s world and this modification of an oil’s viscosity is achieved (with a few exceptions) through the use of polymer thickeners. A monograde oil of a lighter grade is thickened to give it multigrade properties with a polymer thickener. This is particularly useful when the equipment (say an emergency generator) may be required to operate at lower temperatures whilst retaining its high temperature qualities.
Hydraulic oils also use polymer thickeners in the same way to cope with temperature changes whilst retaining their optimal viscosity / temperature characteristics.
CORROSION PROTECTION ADDITIVES
Last but by no means least is an additive that is of specific and vital importance in superyachts that may have periods where engines lie idle during refit or sale. This additive, which is chemically absorbed into the metal, protects these surfaces from atmospheric corrosion, very important where an engine could be little used in the winter season if remaining in Europe. This additive works in tandem with the detergent by having alkaline properties to assist in the neutralisation of acids formed during combustion.
These eight additives are the most well- known, yet as with any spell-book, not all the pages are visible and oil companies will continually research and produce new formulations of additives, as well as new ones too, as the marine environment changes through regulation and progress.
As there is a continuing drive towards getting more power and greater sustainability, so too will additives change, as it is inevitable that oil is combusted during the diesel cycle. Fuels have a direct effect on lubrication too as there is always fuel present in the lubrication in greater or lesser amounts in the sump and as fuels change and evolve so will lubrication additives.
Final words of wisdom – “condition monitor everything if you want to avoid failure – it’s best practice after all and no magic is required”.
For more details visit www.spectro-oil.com
