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20/40 and 20/50 were popular in California for highly modified V8s like the one in your avatar. I live in the San Francisco bay area where temperature might drop below freezing once in 30 years. A 10/ 30 or 5/30 oil in an old V8 might provide protection for low temperatures in most of the country, but here?
With multi viscosity oil the low number is supposed to tell you the vis of the oil at a very low temp. The second number tells you about the vis of the oil at high temp, but 50 vis oil is not 50 vis at high temp.
Certainly old V8s were fed different vis oils depending on where they lived (the climate) and what kind of work they did (developing lots of horseponies at higher RPM or just loafing along in a sedan).Regarding worries with respect to viscosity (5W30 and 5W20), the 30 and 20 suffix is determined by the viscosity at 100 C. And each suffix is a range of permissible viscosity, not an exact number, though you would expect the oil manufacturer to hit the mid-point of the range. But business being business, they will often target the least expensive zone in the viscosity range to minimize their manufacturing costs.
Considering that our engines operate over a wide range of temperatures, and not just 100 C, then this particular viscosity measurement is not greatly meaningful. Impose on this the viscosity drop associated with fuel dilution, and the viscosity increase from oxidative thickening, then we arrive at the conclusion that engines are not very fussy about viscosity. The exceptions being if the oil is too viscous for a cold start, and too viscous to be distributed quickly by the oil pump, then real problems occur.
The reason some car manufactures have switched to 5w-20 is for gas mileage.they feel that thinner the oil creates less drag in the engine= better mileage.
with car companies competing for gas mileage ratings they are doing what they can to compete.The idea that car manufacturers recommend lighter viscosities to improve fuel economy and that they have taken a shortcut to better CAFE ratings appeals to me too.
Honda recommends 5/20 for some VTEC engines and 5-30 for others and this could be suspected of supporting the shortcut idea, but Honda does not have the problem that most other manufacturers have in meeting CAFE standards. Nearly everything they sell in the US gets good or excellent mpg. They sell no real PU trucks. The Ridgeline isn’t really a PU truck and few are sold here.
Certainly there are other manufacturers that are highly motivated to take shortcuts to improve CAFE ratings.
Honda’s small high reving engines are notorious for long life. I doubt they would risk the reputation they have earned to improve their CAFE rating when they have no motivation.
If you could make a good complaint about Honda engines, it would be that they often remain running with no internal problems when the the rest of the car looks like a corpse.Always, always, always, always, always, always, use what is recommended on the oil cap or owners manual for the engine you’re working on. Engineers spend a great deal of time, testing, and effort figuring out what works best in their engine design and you should stick with it.
Eric, I don’t want to go against the grain here man. But for General cars? Daily drivers and normal people. The recommended weight on the cap or manual will work just fine. But when you start getting into very high heat or extreme heat and power applications, Drag racing. Road racing, Auto-X. The Thickest oil you can use as long as the PTW ( Piston to Wall Clearance ) Will allow, It will be the safest against shearing, extreme heat and wear. But this also comes down to the quality of the oil as well. Not just weight. A Solid, Good 5w20 weight will be better then a bad 5w30 weight and so on.
Yes, Manufactures put alot of time into R&D For the Engines they put in there car. But they will use a lighter weight if it means better emissions and MPG just to please the government and emission standards and regulations to prevent them selfs from being fined. Company likes Honda don’t have to worry about it so much. But Company using V8’s and trucks? They do.
I can go on and on, And I will if I must but don’t think certain company’s know best. Sometimes they think with there wallet before they think about there automobiles.
Quoted From Six6vetteguy:
I use 10w-30 in california…5w-30 doesn’t offer enough protection.
There is absolutely no difference in these 2 oils when the oil is at operating temperature (cheaper brands may offer different HTHS properties over branded products).
The only difference is the viscosity index rating for the winter temperatures where 5w is thiner than 10w for cold starts.
W in oil stands for Winter, not weight.
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