oilman Posted October 10, 2013 Report Share Posted October 10, 2013 Engine Oil ViscosityViscosity 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 9.3cstSAE 30 = 9.3 to less than 12.5cstSAE 40 = 12.5 to less than 16.3cstSAE 50 = 16.3 to less than 21.9cstSAE 60 = 21.9 to less than 26.0cstALL 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.SummaryCold start.A 5w-40 will flow better than a 10w-40.A 10w-50 will flow better than a 15w-50A 5w-40 is the same as a 5w-30At operating temperatures.A 10w-50 is thicker than a 10w-40.A 15w-50 is thicker than a 5w-40A 0w-40 is the same as a 10w-40If 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.ukWith thanks to John Rowland of Fuchs/SilkoleneCheersTim and the Opie Oils team Link to comment Share on other sites More sharing options...
J03 Posted October 10, 2013 Report Share Posted October 10, 2013 I've always used 5w 40 Gulf Competition, both NA & now boosted. However, I've noticed that my temps aren't really getting above 95 degrees C. & they're more like 80 on average. In summer that will obviously be different, but would you recommend dropping to a 30 through the colder months? Link to comment Share on other sites More sharing options...
oilman Posted October 10, 2013 Author Report Share Posted October 10, 2013 Have you got an oil cooler fitted? CheersTim Link to comment Share on other sites More sharing options...
J03 Posted October 10, 2013 Report Share Posted October 10, 2013 No oil cooler. I have a higher capacity alu sump, deeper rad, TRD lower temp stat & the rotrex charge is intercooled. Link to comment Share on other sites More sharing options...
oilman Posted October 10, 2013 Author Report Share Posted October 10, 2013 As it's not getting that hot, I would say that you are probably best off with a quality 5w-30, like the Fuchs Pro S. Cheers Tim Link to comment Share on other sites More sharing options...
Monkey Boy 1 Posted October 10, 2013 Report Share Posted October 10, 2013 (edited) Some good info there Tim. Hopefully this will answer many questions that are placed on this and other forums. One question I have is, back in the day when I was riding classic motorcycles, many of them used 'straight' oil, ie.SAE40 or SAE50. I presume that this was just a ref. to the flow at operating temerature and there was no 'cold start' figures It was said that 'straight' oils were better for rollerbearing cranks that white metal bearing cranks. Can you enlighten me if this theory is correct or not. Cheers Simon Edited October 10, 2013 by Monkey Boy 1 Link to comment Share on other sites More sharing options...
oilman Posted October 10, 2013 Author Report Share Posted October 10, 2013 Hi Simon A straight 40 is basically a 40w-40, so basically very very little cold start protection. In most cases with classics, a 20w-50 is often preferable to the straight grades. With roller bearings, Silkolene Comp 4 20w-50 is often a brilliant option for the very best protection. http://www.opieoils.co.uk/p-1123-silkolene-comp-4-20w-50-synthetic-ester-based-4-stroke-engine-oil-for-high-performance-motorcycles.aspx Cheers Tim Link to comment Share on other sites More sharing options...
geraintthomas Posted October 10, 2013 Report Share Posted October 10, 2013 Fantastic information, should definitely be a sticky. Learnt a fair bit from reading that. 1 Link to comment Share on other sites More sharing options...
oaksey Posted October 10, 2013 Report Share Posted October 10, 2013 Me too, thanks Tim Link to comment Share on other sites More sharing options...
Trebor4460 Posted October 10, 2013 Report Share Posted October 10, 2013 Thanks for the useful info... apreciated. Link to comment Share on other sites More sharing options...
KeoGT Posted October 10, 2013 Report Share Posted October 10, 2013 Yea tbh I never truely understood oil, I only ever went on manufacture recommendation and that it was fully synth, apart from that I never understood what the numbers meant Link to comment Share on other sites More sharing options...
daytona Posted October 11, 2013 Report Share Posted October 11, 2013 Well there ya go. I know more than yesterday. Cheers Tim. I knew the first number was about cold and the second one about hot but that was about it! Link to comment Share on other sites More sharing options...
oilman Posted October 11, 2013 Author Report Share Posted October 11, 2013 Thanks, glad you like article Link to comment Share on other sites More sharing options...
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