http://www.opieoils.co.uk/ i was on this site and asked for an oil recommendation, here is the reply. Mathew, Thanks for the mail. For the Golf the 10w-40 semi is fine, you could if you wanted to move up to a 5w-40 full synthetic, there will be no issues i doing this and you will get longer drain intervals, less wear etc. Have a look at Motul, Fuchs and Silkolene. Regards Guy. Opie Oils anyone gone for a 5-40 fully synth before? i take it it will be thinner? mine leaks enough as it is.... may try it tho
5W/40 oil is thicker when its cold, than 15W/40 when its warm. So its okay to use. Basically, the W is a winter rating, at a cold temperature, oil is always thicker at colder temperatures. Its not a physical measurement, just an index.
Utter shוte, the 5w40 is thinner when it's cold. The higher the number, the thicker the oil. so a 5w will be thinner than a 15w on a cold start-up. Once the oil is hot, they will be equally thick.
That should be 5/40 is THINNER when its cold(5) so OK to use as its then the same viscosity rating once its warmed up (40)
Feel free to try it - it's unlikely to cause leaks unless you have gunk stopping your oil seals from leaking. Which a high detergent synthetic may remove. In which case you should really replace them anyway!
No it isn't............ it is SAE 5 when cold. a 15/40 is SAE 40 when it's warm. I did study a bit of tribology, you know......
SAE isn't a unit of viscosity though, is it? Its an index which is based at 2 temperatures, 40C and 100C. I am sticking 100% with my original answer!
Yes, it's based on two temperatures, but you are still wrong......... read up on it a bit, and then decide whether or not you are going to stick with your original answer...... Regardless of whether the SAE rating is a "unit of measurement", it is DERIVED from a unit (nowadays 3 units) of measurement to make it easier for consumers to understand.
Paul C Even without studying fluis dynamics and physics why do you think the 10/, 5/, 0/ oils be generally more expensive than 15 or 20? More money is charged for the wider grade band oils because they are more sophisticated and more desirable. It is desirable to have the thinest oil possible when cold so that it will flow well Duckhams Q was the first really 'trick' oil - a multigrade. At cold temperatures it was as runny as a 'thin' 20 grade oil but as it heats up the molecules form longer chains making it more treacle like and taking on the properties of a 'thicker' 50 oil
And if you don't believe it, try cooling some 5w40 in your fridge overnight, and heating some 15/40 to 100 degrees in a pan. Then see which is thinner........
Reading the chart: 5W/40 oil is 20cSt at 40C and 15cSt at 100C. 15W/40 oil is around 35cSt at 40C and 15cSt at 100C. So, the 5W/40 oil is 20cSt when cold compared to the 15W/40 at 15cSt when warm, ie its thicker when cold than warm.
The arguments against using 5W/40 are not to do with viscosity, its to do with it having a lesser percentage of base oil, because more of it is viscosity modifier. Also, it may have a higher quality rating, so it will have better/more detergent etc in it and could 'wash' off previous deposits from years of using a different quality oil, which might cause issues.
Viscosity modifiers are a tiny percentage of the volume of oil. A higher quality base oil is never a bad thing in my book - and as I aid, if an oil with a better detergent in it removes deposits and causes a leak - then you need to change the seal, because it is leaky and your engine is clogged up with gunk from using cheap oil!
Its not 'cold' for us, but for an engine it represents the first few minutes of running. I guess that's why SAE chose it for their 'cold' viscosity measurement. Viscosity modifier alters the temperature-viscosity relationship, but they cannot make oil thinner when its colder, than it is when its hotter - at least not in the quantities they are used in engine oil.
