just a stupid question...

[Fortecarbon]

Having read the article by Dr. Haas, the "oil bible" and many other oil articles....

If all Synthetic 30 weight oils fall into the same vis. category at 200F, regardless of the cold weight rating. Wouldn't you always want the oil with the lowest "winter" weight possible? eg. 0w-30 ? Why would you ever choose a 10w oil? (Unless maybe the abient temps were 90F regularly)

I cosntantly read "you should try 5w or 10w" etc. and its not making much sense to me?

 

[tpattgeek]

I always wonder the same thing, and my thought is, if the car is designed to cold start with a 5, give it a 5 unless you're at below 0 temps in which you would definitely want a 0. Like he said in the bible, you should want to go LOWER instead of higher. A thinner oil at cold temp provides much better lubrication and protection than one that's too thick for your engine. That's what I gathered from it at least.

And yes, the 10w rule of thumb "for any engine" is very old school.

 

[eljefino]

old school thinking that too big a spread shears down.

 

[RamFan]

Originally Posted By: tpattgeek
Like he said in the bible


Never thought I'd see that on an oil forum.

 

[addyguy]

Many, if not all, 10W-30 synthetics don't use ANY viscosity index improvers (VII's) to make the spread, so they are very shear-resistant. A lot of 5W-30's don't either, bu many do.

Also, 10W-30 synthetics tend to have very, very low volatility rates - as low as half of a comparable 5W-30. In high-stress applications, this may mean less oil loss.

Finally, even though it is a '10W', msot 10W-30 synthetics still have very good cold crank/pumping values, and often behave close to a 5W-30 in cold weather.

For those reasons above, I think 10W-30 synthetics are still a very valid and useful viscosity to consider.

 

[LS2JSTS]

Originally Posted By: addyguy


Also, 10W-30 synthetics tend to have very, very low volatility rates - as low as half of a comparable 5W-30. In high-stress applications, this may mean less oil loss.


+1

I believe that in DI engines a lower NOACK volatility oil will be beneficial. In my favorite brand the 10w is almost 3% lower NOACK than the comparable 5w.

 

[d00df00d]

I only want to add one thing: many high-end 0w-30s are quite shear-stable. GC, for instance. The shear stability thing is more of a rule of thumb than anything.

Other than that minor point, addyguy said it very well IMO.

 

[Steve S]

I discount most the article as nonsense.

 

[Steve S]

Originally Posted By: eljefino
old school thinking that too big a spread shears down.
It does between the parts in high stress areas.

 

[tpattgeek]

Originally Posted By: Steve S
I discount most the article as nonsense.


Then why does BITOG have it on the homepage and act like it's a "must read".

 

[ARCOgraphite]

Because BITOG'ers revel in nonsense!

 

[sangyup81]

Originally Posted By: Fortecarbon
Having read the article by Dr. Haas, the "oil bible" and many other oil articles....

If all Synthetic 30 weight oils fall into the same vis. category at 200F, regardless of the cold weight rating. Wouldn't you always want the oil with the lowest "winter" weight possible? eg. 0w-30 ? Why would you ever choose a 10w oil? (Unless maybe the abient temps were 90F regularly)

I cosntantly read "you should try 5w or 10w" etc. and its not making much sense to me?

You know what's weird about the Xw-30 oils? When you compare a particular brand's offerings, either the supposedly thicker 10w30 is only slightly thicker than the others or is thinner, sometimes significantly.

Examples:

For PP, 5w30 = 10.3cSt, 10w30 = 10.5cSt a 1.9% difference
For M1, 5w30 = 11.1cSt, 10w30 = 10.7cSt an 3.7% difference in the wrong direction

Here's one that will really throw the old timers off
Castrol Syntec 0w30 = 12.2cSt, 10w30 = 10.1cSt a whopping 19.8% difference in the wrong direction!

 

[mechtech2]

forte -
You have used good judgment in appraising the situation.
This is why some say "No oil is too thin at stat up.".
10-30 in kinda obsolete. Why does it exist? If it is indeed as good in cold weather, then let it be labeled so.

BTW,if you get a '0' first number, it denotes a full synthetic. Right now, it can't be done with dino.

 

[CATERHAM]

Originally Posted By: sangyup81
Originally Posted By: Fortecarbon
Having read the article by Dr. Haas, the "oil bible" and many other oil articles....

If all Synthetic 30 weight oils fall into the same vis. category at 200F, regardless of the cold weight rating. Wouldn't you always want the oil with the lowest "winter" weight possible? eg. 0w-30 ? Why would you ever choose a 10w oil? (Unless maybe the abient temps were 90F regularly)

I cosntantly read "you should try 5w or 10w" etc. and its not making much sense to me?

You know what's weird about the Xw-30 oils? When you compare a particular brand's offerings, either the supposedly thicker 10w30 is only slightly thicker than the others or is thinner, sometimes significantly.

Examples:

For PP, 5w30 = 10.3cSt, 10w30 = 10.5cSt a 1.9% difference
For M1, 5w30 = 11.1cSt, 10w30 = 10.7cSt an 3.7% difference in the wrong direction

Here's one that will really throw the old timers off
Castrol Syntec 0w30 = 12.2cSt, 10w30 = 10.1cSt a whopping 19.8% difference in the wrong direction!


You're looking at the kinematic viscosities which do not necessarily correlate all that well with the actual operational viscosity in an engine. You should be comparing the HTHS vis of these oils and then you'd have a better picture on which oil is actually thicker or thinner.
Don't know about Castrol since they don't provide HTHS spec's but PP and M1 10W-30 oils are thicker than their 5W-30 grades at operating temp's and higher because their HTHS vis spec's are higher.
Check out the following post which raised the question before:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2001811&page=1

 

[CATERHAM]

Originally Posted By: Steve S
I discount most the article as nonsense.


That's not a fair comment either.

The gist of what Dr. Haas is saying is true.

But I too have a problem with some some of what he says, such as "ambient temp's having no effect on operating oil temperatures" which anyone who lives in a northern climate knows very cold temp's can inhibit an engine from reaching normal operating temps.
And his personal reference to the 0W-20 he's running is misleading and should be dropped from the piece since it is closer to a 30wt oil.

The problem is that BITOG needs an editor to proof the piece.
The editor need not be an oil expert himself but could send it out to a number of knowledgeable members to review and then have Dr. Haas make the necessary corrections.

As I say, the bulk of what he is saying is basically correct.