How Very High Temperature Affects Petroleum-Based and Synthetic Motor Oils?
One thing that you need to consider is that motor oil is an organic substance and it will slowly break down. Motor oil is generally consisted of base oil and some additives. One concern is at what rate the motor oil is breaking down. As an example, high temperature accelerates the rate of breakdown. Petroleum-based oil breaks down faster, while synthetic oil with good quality may have negligible degradation after 5,000 miles of usages. Additives in synthetic oil are designed to improve tolerance to high temperature, by increasing the temperature of flash point. When the flash point temperature is reached, the motor oil will begin to vaporize inside the engine block. Some components of the motor oil will turn into vapour and expelled through the exhaust system. Usually, the lighter components of motor oil will be vaporized first and this will cause the motor oil to become thicker. It means that the properties of motor oil will change, because the chemical composition has changed as well.
In general, modern engines are expected to be smaller, but still provide equal or more power. This means that engines can run hotter than usual. Higher temperature would put a lot of burden on the motor oil. In general, regular synthetic oil is up to the task. Petroleum-based oil could deal with this condition as well, but not as good as synthetic oil. It means that petroleum oil is more likely to burn off compared to synthetic oil. Petroleum motor oil is refined from crude oil, so it means that petroleum motor oil is not homogeneous with molecules that have different size.
The smaller molecules of petroleum oil will be vaporized more easily. When it happens, sludge and deposits will be more likely to form. They will coat the internal surface of the engine, including the piston and the wall of the combustion wall. It means that if your engine overheats due to the problem with the coolant, you should consider replace the motor oil. If the motor oil becomes thicker, it would become thicker and can’t flow smoothly. Larger molecules of motor oil will also tend to trap heat, instead of circulating it. This will only make the heat accumulation problem to become worse. When your motor oil has passed the lowest flash points a few times before, then the heating blanket effect will become more serious.
On the other hand, synthetic oil isn’t made from refined crude oil. It means that molecules inside synthetic oil have more uniform shape and size. While petroleum-based motor oils have multiple flash points that affect different components, synthetic motor oil has only a single flash point. Burn off will only affects synthetic oil when the temperature is high enough. Synthetic oil should have better job in making the engine cooler. Also, synthetic oil can be around 20 degrees color than petroleum oil in similar situation. So, it means that synthetic oils can slightly do a better job in dissipating heat.