hahanson

Like I stated earlier, the "W" rating is more significant.

There's really nothing I know of that definitively states using 5W30 rather than 5W20 will do any harm to an engine whatsoever. Something like racing your truck in BAJA might specifically recommend a higher viscosity index, but it just doesn't provide any advantages for every day driving. It's kind of like deciding to wear the black suit or the gray suit.... Go take a look at Oil Viscosity Explained.

LariatDude

Yanno, I like you Hahanson. You're an informative guy but at the same time not rude 😎

Stangconv

I just had all my timing done. I'll be doing a short OCI with conventional, then will be putting Syn in in the fall. Just want to make sure its as clean as I can get it.

I like synthetic in the winter. It gets to -40 Here sometimes.

hahanson

As I stated elsewhere in various posts, the number BEFORE the "W" in the viscosity index is the important number.

Regarding, "a better choice for protection" what are you basing that on? Honestly, I don't think it makes much of a difference one way or the other, and there's been no empirical data offered by anyone to say otherwise.

FordTechMakeuloco hypothesizes Ford recommends 5W20 in North America for CAFE standards because they recommend 5W30 in the Middle East or something. Ford came right out and stated it was not due to CAFE standards. Frankly I think it's much ado about nothing either way. There's very little difference in actual viscosity between 20 and 30 @ 100C (212F) -- about 3 pts. There's a significant difference in viscosity between 5W and 10W @ -5C (0F) -- several hundred points.

This is part of the misunderstanding of oil. The problem isn't oil "thinning" as the engine gets hot, the problem is oil "thickening" as temperatures get cold. That's why the "5W" has significance, but the 20 or 30 does not. I doubt if Ford would recommend either if they felt choosing one over the other affected short or long term reliability in any way.

hahanson

Well, I didn't find anything, but it's pretty apparant there are some different tolerances in the cam and crank bearing designs as well as the oil pump. A short passage from Variable Valve Timing – The Next Phase (the entire article is interesting):

To supply the extra oil needed to actuate the two phasers, VCT engines use a new, thicker oil pump that supplies 30 percent more volume than even the higher-volume pump used on DOHC 4V engines. Losses from internal oil bleed-off are reduced with the use of new, rounder (less eccentric near the parting line) main bearings.

650NutKase

cSt @100 is very important to an oil...a 5wXX vs a 10wXX will have no issues flowing in a southern region. However, once that oil is up to temp, the flow characteristics will be more noticeable. A 10wXX will have a higher viscosity vs a 5wXX. As far as empirical data, it boils down to basic pumpability in the oil pump. A slightly heavier oil will increase oil pressure vs a similar, lower weight. The key here is to not over do it, for example, put 20w50 into the crank case (even though some have done it). Also, FordTechMakuloco has come out and said that he has indeed seen fewer phaser failures with vehicles running 5w30 vs the 5w20. Please, do not over look general UOA's with the same engine running both grades. A 30w will typically have a higher TBN vs a 20w. Typically, this means that there is more of the additive "pack" still working. Why? Because a 30w tends to be more shear stable than a 20w. Lastly, oil thickening is more of an issue with NOACK instead of weight. A high NOACK % will usually mean that the oil is more likely to thicken when introduced to higher heat.

650NutKase

Also, if you are going by pour rate, a base II oil will always flow slower than a III (or III+), regardless of the viscosity. Case and point, M1 AFE vs EP. EP has PAO in the base and has consistently shown better cold pour rates in the same viscosity ranges. One last thing, personally, I have also seen less consumption going with a 5w30 vs a 5w20. This is possibly due to the less shear that a 30 has over a 20.

650NutKase

I agree with you on the point of "Does it matter?" Typically, no. In the life span of a vehicle, there will be minute differences of wear between the two. The difference is in high heat, high wear situations where the added viscosity, lower NOACK, higher TBN's will be noticed. Even during these events, you'll most likely notice burn off before wear begins to become measurable.

hahanson

That is not accurate.

Let's say a southern region your startup temperature in the morning is 75 F.

Oil type... Thickness at 75 F...Thickness at 212 F

Straight 30...... 250......................10
10W-30............100............10
0W-30..............40 ............10
Straight 10........30....................... 6

Now you can see that the difference between the desired thickness your engine requires ( = 10 ) is closest to the 0W-30 oil at startup. It is still too thick for normal operation. But it does not have far to go before it warms up and thins to the correct viscosity. Remember that most engine wear occurs at startup when the oil is too thick to lubricate properly. It cannot flow and therefore cannot lubricate. Most of the thick oil at startup actually goes through the bypass valve back to the engine oil sump and not into your engine oil ways. This is especially true when you really step on that gas pedal. You really need more lubrication and you actually get less.

Your reasoning here is flawed at it's most basic level -- 10wXX will have the exact same viscosity as a 5wXX at operating temperatures. The "W" designation has nothing to do with viscosity at normal temperatures.

And you do realize what oil pressure is, right? It's simply a measurement of the resistance to flow. "Basic pumpability" as you state is that a 20 index oil would pump easier and flow better that a 30 index oil. Still, once could point out that they're not THAT different...

Here's something else to think about regarding buying in to the "thicker is better" theory:

"The difference in flow rate, and the difference in shearing generated heat, is why the viscosity used, makes a difference in bearing and sump temperatures. Thicker oil which flows more slowly and generates more heat from shearing, it is not carrying heat away and cooling the bearings as well or as quickly as it could, so that drives up bearing temps. This in turn, causes hotter oil to be coming out of the bearings and into the sump, which is why we see higher temps on a gauge. That is the opposite of what we want.

On the other hand, quicker flowing thinner oil, not only generates less heat from shearing, but it also carries heat away much quicker, keeping bearing temps down. And this means the oil coming out from the bearings, and going into the sump, is also cooler. And that is why we see the cooler sump temps. This is precisely what we saw with the road race engine example above.

If an engine is running hot, use a thinner oil to increase flow, increase internal component cooling, and help keep sump temperatures down. Keeping oil temps down is important to help keep oil below the threshold of thermal breakdown." ~ https://540ratblog.wordpress.com/

Maybe he has; maybe he hasn't. Regardless, it's an insignificant sample size and hardly representative of what may or may not acutally be the case. In fact, on would expect you would see it more on engines running 5W20 as there are simply more engines running 5W20 -- it's what it states to use on the oil cap in bright yellow print (and refelcted in our very own forum poll)! Would be interesting to see actual data, but people being the lemmings that they generally are, don't even think about it and either pour in what they're told to without consideration or simply take it to Jiffy Lube who puts in what's printed on the oil cap.

UOA? TBN? Please clarify.

That goes completely against what you stated earlier. If you're so worried abotu shear and evaporation, then why did you state earlier weight is more significant than conventional vs synthetic?

Synthetics don't require the viscosity modifiers (additives which wear out) that conventional does, has exponentially higher shear resistance (if it wasn't for contaminants, you could run it almost indefinitely) and is much less volatile and far more resistant to evaporation.

And where does this assumption that shear rate is less in a 30 index and a 20 index come from?

The issues regarding oil and what quality oils strive to overcome is not that it "thins" as it gets hot. The issue is that it "thickens" as it gets cold.

Well of course synths and blends flow better than conventional... And again, the difference between the "20" designation and the "30" designation is minimal. As defined by SAE J300 standard, viscosities at 100 C (212 F):

20, 5.6 to 9.2
30, 9.3 - 12.4
40, 12.5 - 16.2
50, 16.3 - 21.8
60, 21.9 - 26.1

Also, shear resistance is completely unrelated to oil consumption.

That's the thing... conventional oil breaks down and wears out much sooner than synthetic, but it doesn't really matter as long as you change it before it's bad. Synthetics, in general simply take more abuse.

Synthetic oil is much better for cold starts (even if "cold" happens to be 75 F), but when is the advantage noticeable? 50k miles? 100k, 300k?

Huge difference between a "W" rating of 5 and a "W" rating of 15. But how long will it takes before the differences bear out in actual wear and tear?

Much less significant difference between a "20" rating and "30" rating -- and as stated above there are plenty of advantages in the "20" (with data to support it).. and I've been offered opinions but have been shown absolutely nothing that 5W30 is better than 5W20 but again, to what conclusion? After 100k miles is the engine running 10W30 going to be significantly better or worse than the one running 5W20? Probably not. Maintenance will have a much more significant impact. At what point, if ever, will a difference be noticeable? The best answer to that: It's anyone's guess...

I do believe that a synthentic (or at least a blend) 5W20 is the best for daily drivers based upon available information. I also believe that if one chooses to run 5W30 instead, it will be neither significantly better or worse than running 5W20. If one prefers to run conventional oil of those viscosity ratings, they won't experience significantly better or worse results either, as long as they observe proper OCI for their driving habits.

650NutKase

You and I have different opinions on the matter, but I respect that. I'm glad you and I both recognize that maintenance FAR out weighs oil preferences. BTW all this information that I have gathered has been through independent UOA's that I, and a few other acquaintances have gathered, as well as multiple connections with members on the BITOG site.