Hi, What does 20W-50 for 4 stroke engine oil means?
A good practical explanation. I'll just add, before someone draws the wrong conclusions, that even a 0W-40 oil is still more viscous (thick) at low temperatures than at high. A common misconception is also that a 0W-40 should be thinner than a 20W-40 at high temperature. The only thing sure is that both fulfil the requirements for grade 40 at approximately 100 deg C.
The "W" after the 20 means that this oil can be pumped at temperatures as cold as one would expect to be able to pump straight 20 weight oil. The 50 at the end means that at or about operating temperature (212ºF IIRC) it has similar viscosity as that expected of a straight 50 weight oil at the same temperature. Notice the "W" winter rating is only the ability to pump the oil. The threshold is set where API/SAE felt a real world engine oil sump might draw and pump oil. This so-called multi-grade oil is really just an extended temperature range oil. It doesn't thicken as much when it gets cold, and it doesn't thin as much when it gets hot, as so-called single weight/grade oils. As others point out its thinner when hot and earns its "50" than when cold and earns its "20W."
The oil is 20 weight oil with the lubricating property's of 50 weight. Very good oil for the hot weather.
No, it doesn't mean that at all. The W indicates suitability for Winter use. The first number indicates a dynamic viscosity at 0 deg F *equivalent* to a straight grade SAE 20. The second number indicates equivalence to a straight grade SAE 50 at 100 deg F.
You are so right. When will this old myth die ? To be very precise, this was the original idea of the W numbering system. It may or may not still be approximately true. The current W grades are just a number of criteria to be met with no reference to any "equivalent oil". And the temperature for the main (or "hot") grade viscosity measurement is close to 100 deg C (200 deg F ??). And there is no need for any equivalent oil here because this IS the viscosity test for grade 50 oil.
Right, and I believe the low-temp test is dynamic vis, while the high-temp test is kinematic vis. You're in Sverige? Do Europeans use the SAE designations, or is there an EU specific (DIN/ISO?) scale for multigrade oils?
Yes. And next week even better, I go back roads touring, mountain riding, sheep dodging in Norge on my XT600. Yes, at least as far as I've seen it's 100%. O T O H the significance of the API service ratings (that's the name ?) like SJ or CC are loosing importance as most car manufacturers are going for extreme oil life and develop their own tests and specs while motorcyclists get more and more aware of the JASCO ratings. Honestly, I don't know. I never heard of one.
Will it okay to use this engine oil grading (ie. 20W-50) for a bike that the manufacturer recommended 10W-40?
Wheather or not there are any VI improving additives in a 20W-50 oil is wholly dependant on the choise of base oil(s). No engine oil has ever been more viscous hot than cold ! The reason behind the "thin" oil is that you drain the oil while the engine is still warm. If the engine is on it's last legs or is used only for extremely short rides it might suffer from fuel dilution. VI improver breakdown is a possibility if the oil is used for a long time, has cheap (mineral) base oil, a large spread between W and hot rating (e.g. 10W-40) and the engine is worked hard. AFAIK, the whole VI additive debacle was started by a number of car engine breakdowns, but I might be wrong.
