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Can we use diesel engine oil in petrol engine?


amitaj

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I heard someone saying very confidently that we should use the diesel engine oil in petrol engine, as it has much better cleaning detergent and better lubrication than the petrol engine oil for extending the long life of petrol engine. Companies uses better lubricants and detergent for diesel engines, as diesel usage create lot of sludge and sticky black substance that require hard chemical in engine oil to keep it clean.

Is it really true and advisable to use diesel engine oil in petrol engine?

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It is true that the detergents in diesel oil are stronger than those used in petrol engines, but that is because diesel oil detergents have to deal with combustion products that are completely different from those formed in petrol engines.

In fact, some combustion products found in diesel engines do not occur in petrol engines at all, so by using diesel oil, you have no detergents that are designed to deal with petrol combustion products. Moreover, the friction modifiers in diesel oil are made differently, and while all friction modifiers contain zinc as the base material, it is the amount of zinc relative to other additives that make friction modifiers effective.

It is also true that the total amount of additives in diesel oil is about twice that of petrol oil, so by putting the additional additive load on a petrol engine, you reduce the amount of available base oil by about 50% as well, which can have serious effects on the durability of the engine because there is less oil to carry the additives to where it is needed. One effect of this to raise the oil's temperature, which is very bad for the oil and the engine. While there are more additives, they are of the wrong type and proportions to what petrol engines require, so despite having more additives, you can destroy a petrol engine in less than 1000 kms.

This is mainly because the detergents in diesel oil removes the lubricating film of oil on the cylinder walls in a petrol engine. This increases wear because the rings depend on this film both for lubrication, and to form a seal to contain the combustion pressure. Without this film on the cylinder walls, you get increased blowby, increased oil consumption, and a severe loss of compression. 

There are other problems as well. Diesel oil is generally thicker than petrol oils, which means that the extra effort it takes to pump the oil around the engine can increase the temperature of the oil to the point where additives start to break down. The general rule is that for every ten degrees you raise the oil temperature above the recommended max temperature, you reduce the useful life of the oil by about 50%.

Add to this the fact that when the engine is cold, the oil might be too thick to pump around the engine, which means that for the first few minutes of operation, a petrol engine might not have sufficient lubrication to prevent extreme mechanical wear.

You are far better off using the correct oil for your engine- using oil designed for diesel engines in a petrol engine is a very bad idea, and it WILL destroy your engine in very short order.

 

 

 

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Thanks treks, for very educating and theoretical information but the guy who was claiming was the guy speaking to car technicians and while he was explaining this theory even the car technicians just noded their head and said "may be". That guy claimed that he is using this since one full year in his car w/o any problem. I don't know that guy personally but I was there present in that conversation as a third person, and kept quiet while they were talking to not to sound dumb in front of all people.

Whatever it is, I think you answered my curiosity and I wouldn't bother experimenting this with any of my car for the sake of safety and associated risk involved.

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