Originally Posted By: Trav
I said it might be, maybe i should have said optimal instead of correct.
Take the Nissan VQ for an example these engines routinely produce better UOA's with the 0w40 but he wont know until he tries it out and compares the two.
I am not convinced 20w is optimal for anything if it was then other countries would be using it also and their fuel prices are in most places double and more than the US.
CAFE is the worst sort of political control mechanism ever foisted on the consumer bar none.
Quote:
yet strong enough for sustained use, seems to make a lot of sense. All I've seen is that manufacturer's have tested their engines over time to see if they're suitable for taking on 20 weight oils.
Only in the most mundane grocery getters. Chrysler for example specs 0w40 in anything with more HP than a lawnmower with seats.
Well optimal is a loaded word because it is used without stating what we're trying to optimize.
Firstly, if the engine will outlast the car on 20 weight oil, and 20 weight oil produces fuel economy savings, then 20 weight could be claimed to be optimal even if, despite cold start wear advantages, it overall caused more wear than 30 weight.
I think studies have shown that 20 weight oil saves fuel, and Ford did rigourous testing. Toyota's back spec to 20 weight engines is particularly interesting in that some engines that people think are the same can take 0w20 in recent years, others can take 5w20 in less recent years, and others have to stick to 5w30 in older years.
In Toyota's case, there must be some serious engineering and statistical analysis going on to figure out which engines can and cannot go on the lighter oils.
So I think we are left more with the question of explaining why other countries don't spec 20 weight oil rather than why the US does spec it.
Firstly, I would contend that since most engines run a good part of their time on much higher viscosities than operating temperatures, and that these viscosities at 40c range from the 40's for 20 weight to the 70's for 40 weight, and subsequently much higher at 20c or 0c, that the difference between viscosity of 8 for 20 weight or 10 for 30 weight, is anyhow negligible.
So for me, the question is really answered by looking at the economics of the effort required by the same manufacturers to spec 20 weight outside of the US and what incentive they have to do so.
1) They would have to prove that in the TYPICAL operating conditions in a particular country that there would be still be enough reliability in a switch to a lighter oil. Remember, in the US they have done this, but the TYPICAL operating condition is not the same
2) In these other countries, oil is typically more expensive, and 20 weight oil is going to be even more expensive. So there are many switching costs if they started to specify lighter oils.
When I lived and drove in the UK, the traffic was terrible. Typical journeys were stop start, never exceeding 50mph, often crawling along in traffic. Everywhere is city driving and engines were smaller. I would say that compared to the US, it was a style of driving that on the typical day produces much far more strain than the typical day in the US.
So, to spec 20 weight in the UK would mean verifying in field testing that it worked. If it worked, it would mean then making sure 20 weight oil was supplied to dealers and shops. The 20 weight oil would apply to a fraction of the vehicles out there as the engines were slowly tested, and everybody would be complaining about the higher cost of oil and the complication.
In the US, there was a distinct event, CAFE regulations, that provided an incentive for a manufacturer to work on testing and making engines compatible with lighter oil. If a manufacturer saw profit in going through this effort, then they would put in the wholesale effort of moving that way. But to move that way, they had to be sure through engineering and testing that 20 weight oil would work. There was probably some threshold vs 30 weight oil that they applied that would not result in an amount of premature failure that would impact consumer perceptions.
This is what I think has happened and what explains the difference between countries.
The US has an incentive to move this way and some manufacturers have taken it.
Others in the US have either not explored the incentive, or figured it would not financially benefit them.
Outside of the US, since the manufacturer is not paying for fuel or paying a penalty, and the fuel economy improvement is so small from an advertising point of view, and the switching costs for them to do the testing, for consumers, dealers and others involved in oil changes is so high, they have no reason to move to lighter oil.
