Engine Oil Codes Explained, SAE (Society of Automotive Engineers) numbers explained/Viscosity

Engine Oil Codes Explained, SAE (Society of Automotive Engineers) numbers explained/Viscosity


I just want to give a quick explanation of what these numbers mean when we see them on the front of oil cans so looking at 5w30 we’ve got two sets of numbers the 5w and the xxx it might be easy to start with the 30 this number relates to how the oil performs at 100 degrees centigrade then this number relates to how the oil performs when the oils cool so let’s have a look at list number first and now we get to this figure of 30 so in order to get this figure oil heated to 100 degrees centigrade is passed through what we call a visco meter or a viscometer when it enters the viscometer and runs straight through it’s timed and depending on how quickly it runs through a reading is given and that reading relates to its s a/b number now the slower it travels through here at this temperature then the higher the number is given the higher the SAE number the faster it travels down here the lower the SAE number so this all relates to its viscosity or its thickness the faster travels through the viscometer the lower the viscosity and the slower travels through the viscometer the higher the viscosity so the thicker the thinner travels through quicker the thicker travels through slower and that’s where we get these numbers from so the oil we are talking about as a viscosity of 30 thickness of 30 at 100 degrees centigrade so when we talking about the grade of oils this is where the last numbers come from and their numbers are SAE numbers which have been determined from our visco meter readings and the reason it’s tested at hundred degrees centigrade is because that’s considered a working temperature for the average engine but as most of us know oils at different temperatures react differently they have different consistencies different viscosities the important thing here is that these figures are for tests at this temperature so the oil condition relates to this temperature if we cool the average oil down there’s a tendency to go thicker the warmer it gets the thinner it gets and the cooler it gets the thicker it gets so the warmer it gets the lower the SAT numbers and the cooler gets the higher the SAE numbers the trouble with that is that when we come to start an engine particularly a car engine at a more advanced nowadays we need the oil to be thinner so that the oil can get into the parts of the engine straight away and do a real good job of lubricating everything and the trouble with getting thicker is the parts of the engine that need lubricating from as soon as you turn the key don’t actually get lubricated as much as they need to be so really then when the engines cool hasn’t run for a while this number should go up the temperature will have come down making the oil thicker but the clever thing about our oil is its chemical composition makes it so that in cooler conditions it actually acts like an SAE five so that that oil now it a cooler temperature is thin so that when we first start the key of the car the oil is nice and thin and lubricates where it needs to from the moment we start the key and when it gets up to temperature it acts like an SAE 30 so that it’s not too thin because if it gets too thin at this temperature again it will lose its lubricant efficiency and put wear on the engine the way I remember with these numbers is this w here I associate with being winter so this is the winter condition the cold condition of the oil and of course the second number is what it’s likely 200 degrees centigrade so we can see it acts like an SAE 5 when it’s cool when it gets up to temperature 200 degrees centigrade it acts like an SI 30 and it also relates to these other numbers here any numbers that are found on an oil can now can work out what they are the second number always relates to the viscosity of the oil at hundred degrees centigrade and these figures with the W’s always relate to the viscosity of the oil when it’s cruel so I’m sure you’ve seen oil cans that say you’re simply SE a 30 well we know what that is now it just simply means that this type of oil has been tested at 100 degrees centigrade and it’s got a viscosity SAE rating of 30 there’s no number at the beginning because this oil isn’t designed to be used and work efficiently when it’s cool this oil has only been tested at a hundred degrees centigrade and we know this much about it and this is mainly used for things like lawnmowers more seasonal things that have a much more basic engine but that don’t need that same critical amount of lubricant from when you first start also we don’t generally use lawnmowers in the dead of winter when it’s really cold etc it’s not just lawnmowers though it can be various of the garden machinery etc as we know different engine manufacturers recommend different grades of all and that’s all down to the way they engineer their own engines as to which oil is best used for instance if we’ve got an engine with a turbocharger and a quite a night performance one from a cold start as soon as we turn the key we need oil to get hooked to the turbocharger so the oil needs to be quite thin to do that and also without rollick topics if the oil is too thick then not enough oil could get up to the topics and it could cause problems some might be a little more basic and don’t actually need them specs so really we just need to check manufacturer specifications on our own engines a very big thank you for watching


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