When we took our CRV to the dealer, AFTER the warranty ran out, they suggested going to a 5w20 due to possible fuel dilution issues. I thought Europe used 5w20 as their default? Not sure.
Why wouldn't a 5w50 be better than a 5w40?
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When we took our CRV to the dealer, AFTER the warranty ran out, they suggested going to a 5w20 due to possible fuel dilution issues. I thought Europe used 5w20 as their default? Not sure.
Patman
Staff member
That recommendation makes no sense. Going from a 0w-20 to a 5w-20 does absolutely nothing to combat the effects of fuel dilution. You want an oil with a thicker viscosity, not an oil with a different winter rating. The dealer should have recommended the switch to 5w-30 or 0w-30.
I agree with this. Diminishing returns.
If you look at the base stock my guess is the base stock on the xxw-40 is better.
If you look at wear studies HTHS wear results is your normal S curve, which generally seems to pass the fat part of the curve somewhere around 30-40 weight.
Not saying you couldn't run xxw-50 in a engine specd for 40 weight, but my guess is the return would be much less than going from 20 to 30 for example.
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Patman
Staff member
I don’t think there are that many applications that would benefit from a 50 grade over a 40 grade. At that point you’re just losing more horsepower and fuel efficiency
Bingo. Every oil is too thick until the instant it's too thin. The question is how many "too thin" instances can be tolerated against the harms of "Too thick" in a particular usage.
If you never had to shut an engine off, you could use an SAE 60 forever quite satisfactorily in terms of wear performance for many vehicles. Not so much the economy or efficiency, though.
agreed.
If the HTHS is 4.2 or higher, there's almost no further advantage to going thicker.
Rather, the advantage of going thicker might be in building up some margin against losing HTHS. For example, if you have a dilluting TGDI, perhaps even a 50 grade is worth considering if that's what it takes to keep enough HTHS for your full OCI.
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That makes sense. Just watched some video's. I think the curve explains some of what I was asking...
So when an engine is starting, its in "Dry Friction." Surface irregularities on the bearing need to be compensated for by the oil thickness as hydrostatic pressure hasnt kicked in. At higher RPM friction is reduced by RPM/pressure AND the curve is affected by viscosity...
So, based on that, wouldnt a higher weigh oil help more on dry start up? A 10w? a 15w? Maybe that what I was trying to say in reference to a thicker oil "clinging" to the bearing or already being in place. On dry start up, until pressure/velocity builds, all the lubrication is due to oil thickness, which has to overcome bearing irregularities. And these irregularities increase with bearing wear...
Wouldn't a thicker oil also affect the slope of the curve in phase 3?
Hypothetically, if an older engine has .003 bearing clearance, and new was .001, why wouldn't a higher viscosity oil fill the gap better and lower wear?
We have all heard of car salesman throwing in very thick oils or honey goop to quiet rod knock just to sell a car... It does affect the rod knock, albeit for a very short time... Ergo, wouldn't a thicker oil also have a positive effect beyond just shear resistance?
Engine clearance standards haven't changed in decades.
If your engine is already worn out and your looking for a very short term fix, that is an entirely different question.
Because microscopically there is no contact in their situation. Going from "no contact" to "still no contact" has no effect on wear.
Rod big ends are somewhat you unique because the journal bearing is constantly reversing. And yes, thick oil can reduce rod knock. But a rod knocking engine is terminally ill regardless of oil used.
An engine is never in "Dry friction." Even a newly built engine has assembly lube.
Dry means no lubricant. That's never the case in an engine where oil residue is always present.
Hah, that's actually a real product. Only slightly surprised, and mightily amused. I wouldn't mind a bottle of that as shop art.
https://www.atlanticoil.com/oil/stop-smoke-40w-70/
FIrst part of your question. No.
Second part a heavier grade would place you farther to the right of the curve where friction and heat increase at the expense of no meaningful change in wear.
10w, 15w, or any number in front of the W(winter rating) does not indicate the viscosity or thickness. It only means the lowest temperature rating you should start the engine at. The grade (number after the W) indicates thickness.
Per Castrols website...
The low temperature viscosity of the oil is a measurement that simulates starting a car on a cold winter day. That value has the letter “W” after the number and has a dash after the W. For example, if the oil is a 5W-30, the 5W part describes the viscosity of the oil at low temperatures. The lower the number, the faster the oil will flow at vehicle start up.
https://www.castrol.com/en_us/united-states/home/products/our-brands/viscosity-grades.html
But you aren't really understanding what you're reading. Confusion over what the winter rating means, what it does not mean, and when it has meaning is very common.
The winter rating is only measuring something at a certain temperature. Above that it has no meaning. Flow is not really relevant, except for flow near the oil pump pickup tube. As long as the oil flows to the pickup tube it will flow in the engine due to the oil pump. What matters is pumpability. If an oil cannot be pumped then the game is over. That is what the winter rating really represents.
For a 5W rated oil it means the oil is guaranteed to be pumpable at temperatures of -30 or so. Above that temperature a same-grade oil with a 0W rating may be thinner or thicker. There is no guarantee of that given by the winter rating.
Friction (especially "dry friction", whatever that is) is not what is going on here.
Again that number is the winter rating where it is safe to start. It is not a thickness.
It's technically the ability to pump at really low temperatures. It may not directly correlate to thickness at ambient temperatures during cold starts. And for the most part, I've heard it's not that big a deal since there's usually some sort of sacraficial antiwear additive that protects during cold starts.
I've seen stats where a typical 0W-40 was thicker at typical spring/summer temps than a 5W-20.
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