Did you know you can’t mix synthetic diesel motor oil?

If you thought all oils are the same then you wouldn’t understand why you can’t mix synthetic diesel motor oil. You may be in for a shock when you hear why you can’t mix synthetic diesel motor oil if you want your engine to last.

You can’t mix synthetic diesel motor oil because of the diesel engine requirements.

Although petrol and diesel engine oils aren’t that different the different functional requirements between the 2 engines are the reasons that you can’t mix synthetic diesel motor oil with a petrol classified lubricant. In essence, petrol and diesel motor oils have the same anatomy and both perform the functions of lubricating moving parts, aiding cooling and removing unwanted deposits. Both are formulated from the blending of base oils and additives to achieve a set of characteristics that perform best for the particular engine type.

Although both spark ignition and compression ignition engines are classified as internal combustion engines their lubrication requirements are very different. Because of combustion by-products and increased blow-by, diesel engines produce high levels of particulates that require scrubbing. At the same time the high cylinder pressures also generate high cyclic forces on the bearing surfaces.

The most important reason why you can’t mix synthetic diesel motor oil is probably the most important quality of a lubricant - viscosity. For any engine to be adequately protected the lubricant’s viscosity needs to be correct so that the engine oil is pumpable at the lowest start-up temperature while still protecting the components over a wide range of operating temperatures.

Because of the higher cyclic loads produced by the diesel engine, this engine lubricant tends to have a higher viscosity than regular petrol-engine oil. This higher viscosity, in a petrol engine, would create lubrication problems; particularly with cold start lubrication of the valve train.

The heat generated from internal fluid friction, caused by the pumping effects to pump the thicker oil, can reduce engine life; for every 10 degrees C increase in operating temperature, the life is cut in half. This is certainly an unwanted side-effect and an important reason why you can’t mix synthetic diesel motor oil.

Additive Levels in petrol and diesel oils are different underlining the fact that you can’t mix synthetic diesel motor oil.

To deal with the inherently high levels of particulates resulting from the combustion process in the diesel engine, diesel motor oil tends to have higher concentrations of detergent additives. The most prevalent being overbase detergent additives. These additives are critical in Diesel motor lubes because they neutralize acids and remove varnish and soot trapped in the oil.

Diesel engines create a great deal more soot and combustion byproducts. Through blow-by past the rings, these find their way into the crankcase, contaminating the oil. Thus for diesel engines the lubricant carries a proportionally higher detergent load.

Unfortunately you can’t mix synthetic diesel motor oil with petrol oils because of this: The extra additive load would be devastating to performance and engine life on a petrol powered vehicle. The detergent will aggressively try to clean the cylinder walls, thereby having an adverse effect on the seal between the rings and liner, resulting in a loss of compression and efficiency.

Another reason why you can’t mix synthetic diesel motor oil and petrol engine lubricant has very little to do with lubrication and more to do with the byproducts of combustion and emissions control: Lead, zinc and phosphorus can severely damage the catalytic converter’s (That’s fitted to reduce emissions) ability to perform. Diesel engine oils, because of the higher loads encountered, have higher anti-wear (AW) concentration in the form of zinc dialkyldithiophosphate (ZDDP).

This is one of the main reasons you can’t mix synthetic diesel motor oil in your gasoline engine.

So if you can’t mix synthetic diesel motor oil with petrol engine oil, how do you tell the difference between petrol and diesel engine oils? On the label, you’ll find the API (American Petroleum Institute) service designation. This designation will either start with an “S” (spark ignition) for petrol engines or a “C” (compression ignition) for diesel engines.
 At Habot Oil we understand that you can’t mix synthetic diesel motor oil; that’s why we offer you quality synthetic lubricants for both. Contact us for professional advice on which of our products best suit your requirements.