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What is the difference between diesel and gas engine oils?

In many ways, diesel and gas engine oils are a similar type of lubrication that are designed to serve the same purpose. They are both engineered by blending a base oil with a specialised additives package in order to achieve a specific set of performance properties. However, from this very basic definition, they begin to alter course. In the following sections, we’ll examine each lubricant type’s required performance for the different kind of engine they serve.

Understanding the catalytic converter and emissions

A catalytic converter is the carefully designed housing that includes porous metal filler and is located in between the muffler and engine within a vehicle’s exhaust system. It has the important role of converting the toxic emissions issuing from the engine into stable by-products before they are released into our atmosphere. However, some of these combustion by-products, such as zinc, phosphorus and lead, can severely disable the converter’s capability to perform this task. This is where the first key difference lies between the diesel and gas engine oils.

Diesel-type engine oils have a much higher anti-wear load that takes the form of a chemical compound called zinc dialkyldithiophosphate, or ZDDP for short. The catalytic converters used in diesel systems are engineered to be able to cope with this issue, while the gas-based systems are not. For this reason, vehicle owners must never substitute gas engine oil with diesel engine oil in a gasoline-powered engine.

Viscosity

The single most crucial property of any lubricant is viscosity. When an oil is created, getting the correct viscosity is of utmost importance for each application it serves to meet individual requirements. The viscosity selected must be able to be pumped at the lowest possible start-up temperature, while always protecting components at the in-service temperatures needed.

In most cases, diesel engine oil will feature a far higher viscosity. If oil with this high-level viscosity was put in a gas-powered engine, numerous problems can arise. The first issue is heat generation of internal fluids caused by friction. For every 10 degrees Celsius added in heat, oil life will be cut in two.

The second issue is the pumpability at low temperature of higher viscosity oil. In cold starts, engine oil can be incredibly thick and more difficult for the dedicated oil pump to provide oil to the engine’s key components. This leads to premature wear, as all components start interacting without adequate lubrication to protect them.

Additives

Diesel engine oil has far more additives than gas engine oil per volume. Typically, the most prevalent additives are over-based detergents. This type of additive has multiple roles, but its two main jobs are to clean and neutralise acids. Diesel-powered engines create high volumes of soot and combustion by-products. These contaminants are forced into the crankcase, leaving the engine oil to cope with them.

Added to a gas engine, the impacts of this additive are devastating. The detergent attempts to clean up cylinder walls, causing damage to the seals and resulting in lost efficiency from lack of compression.

Always use the correct type of engine oil to avoid loss of performance and damage to equipment.

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