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oilman

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oilman last won the day on February 13 2017

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    Seat Leon Cupra

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    http://www.opieoils.co.uk
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  1. Engine Oil Viscosity Viscosity is the most misunderstood aspect of oil and yet it is the most important. Viscosity is the force required to shear (break) the oil at a certain speed and temperature. Oils work because they have viscosity; the drag of a rotating part pulls oil from a low-pressure area into a high pressure area and “floats†the surfaces apart. This is called “hydrodynamic lubrication†and crankbearings depend on it. Oil must be capable of flowing at low temperatures, so that it gets around the engine in a fraction of a second at start-up and must protect engine components at high temperatures without evaporating or carbonising and maintain adequate (not excessive) oil pressure. Many people think that the thicker the oil, the better the protection, but if the oil is too thick, it will not flow properly, leading to reduced protection. The numbers on every can of oil indicate its performance characteristics when new but there are many misconceptions on what these numbers actually mean. For multigrade oils you will see two numbers (for monograde oils only one). The first is followed by a “w†and is commonly 0, 5, 10, 15 or 20. The second number is always higher than the first and is commonly 20, 30, 40, 50 or 60. The first and second numbers ARE NOT related. The “w†number (0, 5, 10, 15 or 20) When multigrade oils first appeared, a low temperature test called “w†(meaning “winter†not weight) was introduced. Using a “Cold Crank Simulator", the test measures the oils ability to flow at low temperatures. ALL oils are THICKER at low temperatures than at high temperatures but the lower the “w†number, the quicker the oil will flow at low temperatures. The second number (20, 30, 40, 50 or 60) This number is known as the SAE (Society of Automotive Engineers) number and is measured in “Centistokes†(cst) at 100C. Centistokes (cst) is the measure of a fluid's resistance to flow (viscosity). It is calculated in terms of the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the thicker the oil. An oils cst at 100C determines its SAE rating within the following parameters. SAE 20 = 5.6 to less than 9.3cst SAE 30 = 9.3 to less than 12.5cst SAE 40 = 12.5 to less than 16.3cst SAE 50 = 16.3 to less than 21.9cst SAE 60 = 21.9 to less than 26.0cst ALL oils labelled 40 must fall within the SAE parameters at 100C so everything from a monograde 40 to multigrade 0w-40, 5w-40, 10w-40, 15w-40 or 20w-40 are approximately the same thickness at 100C. Some oil companies label oils as SAE 35, 45 or 55, but as you can see from the above figures, there isn't a SAE 35, 45 or 55. This "could" be because they are approximately on the boundary of the two grades, but as we don't deal with any of those I can't really comment further. Summary Cold start. A 5w-40 will flow better than a 10w-40. A 10w-50 will flow better than a 15w-50 A 5w-40 is the same as a 5w-30 At operating temperatures. A 10w-50 is thicker than a 10w-40. A 15w-50 is thicker than a 5w-40 A 0w-40 is the same as a 10w-40 If you look above, you will see that the figures quoted do not indicate at all as to whether the oil is synthetic or mineral based... Well except for 0w oils as synthetic PAO basestock is required to acheive this viscosity. Generally the oil you use should be based on the manufacturers recommendation found in the owners manual, but then modifications, climate and the type of use can affect that recommendation. If you are unsure of what is the correct recommendation for your car and would like to know more please contact us here oilman@opieoils.co.uk With thanks to John Rowland of Fuchs/Silkolene Cheers Tim and the Opie Oils team
  2. Depends what oil you are using? At those temps a decent 5w-40 or 5w-30 is more than up to the job. Cheers Guy
  3. If you are modding your car and adding BHP or using it off road then consider your oil choice carefully as the stock manufacturers recommended oil will not give you the protection that your engine requires. A standard oil will not be thermally stable enough to cope with higher temperatures without "shearing" meaning that the oil will not give the same protection after a couple of thousand miles as it it when it was new. Let’s start with the fundamentals. An engine is a device for converting fuel into motive power. Car enthusiasts get so deep into the details they lose sight of this! To get more power, an engine must be modified such that it converts more fuel per minute into power than it did in standard form. To produce 6.6 million foot-pounds per minute of power (ie 200 BHP) a modern engine will burn about 0.5 litres of fuel per minute.(Equivalent to 18mpg at 120mph). So, to increase this output to 300BHP or 9.9 million foot-pounds per minute it must be modified to burn (in theory) 0.75 litres. However, fuel efficiency often goes out of the window when power is the only consideration, so the true fuel burn will be rather more than 0.75 litres/min. That’s the fundamental point, here’s the fundamental problem: Less than 30% of the fuel (assuming it’s petrol) is converted to all those foot-pounds. The rest is thrown away as waste heat. True, most of it goes down the exhaust, but over 10% has to be eliminated from the engine internals, and the first line of defence is the oil. More power means a bigger heat elimination problem. Every component runs hotter; For instance, piston crowns and rings will be running at 280-300C instead of a more normal 240-260C, so it is essential that the oil films on cylinder walls provide an efficient heat path to the block casting, and finally to the coolant. Any breakdown or carbonisation of the oil will restrict the heat transfer area, leading to serious overheating. A modern synthetic lubricant based on true temperature-resistant synthetics is essential for long-term reliability. At 250C+, a mineral or hydrocracked mineral oil, particularly a 5W/X or 10W/X grade, is surprisingly volatile, and an oil film around this temperature will be severely depleted by evaporation loss. Back in the 1970s the solution was to use a thick oil, typically 20W/50; in the late 1980s even 10W/60 grades were used. But in modern very high RPM engines with efficient high-delivery oil pumps thick oils waste power, and impede heat transfer in some situations. A light viscosity good synthetic formulated for severe competition use is the logical and intelligent choice for the 21st century. You must seriously consider a "true" synthetic for "shear stability" and the right level of protection. Petroleum oils tend to have low resistance to “shearing†because petroleum oils are made with light weight basestocks to begin with, they tend to burn off easily in high temperature conditions which causes deposit formation and oil consumption. As a result of excessive oil burning and susceptibility to shearing (as well as other factors) petroleum oils must be changed more frequently than synthetics. True synthetic oils (PAO’s and Esters) contain basically no waxy contamination to cause crystallization and oil thickening at cold temperatures. In addition, synthetic basestocks do not thin out very much as temperatures increase. So, pour point depressants are unnecessary and higher viscosity basestock fluids can be used which will still meet the "W" requirements for pumpability. Hence, little or no VI improver additive would need to be used to meet the sae 30, 40 or 50 classification while still meeting 0W or 5W requirements. The end result is that very little shearing occurs within true synthetic oils because they are not "propped up" with viscosity index improvers. There simply is no place to shear back to. In fact, this is easy to prove by just comparing synthetic and petroleum oils of the same grade. Of course, the obvious result is that your oil remains "in grade" for a much longer period of time for better engine protection and longer oil life. If you would like advice then please feel free to ask. Cheers Guy
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