30 or 40 weight vs. 10W-30 or 15W-40

[ledslinger]

For summer use, over 50 degrees F, what are the pluses and negs of running a straight weight oil instead of a multi-visc?

The straight weight will cause a slight but likely undetectable fuel mileage reduction until warmup, but will offer more resistance to breakdown due to lack of VI.

Years ago I was told that BMW motorcycles specced straight weight oils partly because they have more lubricant since they have no VIs.

Are we missing out on running more robust oils by avoiding stright weights in the summer?

Would a 30 wight oil test out as a 15W,20W,25W-30 anyway? A straight 40 a 25W,30W,35W-40?

It seems to me that the advantages of running straight weight oils outweigh the disadvantages. Unless these oils are considered outdated by the manufacturers and they don't use top quality ingredients or research.

 

[Steve S]

I worked for a company Forklift dealership in the San Francisco Bay area that used Delo straight 30 in compressors ,company cars ,Service vans their semi trucks ,the fleet of rental/lease forklifts [over 300] and all the outside equipment they serviced. In the 17 years I do not remember any failures due to the oil and the vans engines would outlast the chassis they were Ford E350 vans with gasoline engines. I use a multi visc because it covers all the temps I will encounter through the year.

 

[BobFout]

What vehicle is in question?

 

[BuickGN]

I ran Amsoil ACD straight 30wt in my TL since new to 75,000 miles and now Redline 5w-30 which uses no VIIs so technically it's a straight 30 too. The Amsoil also qualified as a 10w-30 but used no VIIs.

You will likely be crucified for suggsting anything other than a 0w-10 around here but in a mild climate I see mostly positives going with a good 30wt. Of course by good I mean a synthetic straight 30wt that will qualify as a 5w or 10w.

 

[fdcg27]

I think maybe climate matters more than engine.
In the right temperature range, a straight 30W would be just fine.
There are members here who have tried it.

 

[440Magnum]

Most modern synthetics in 5w30 have few or no VIIs, so the whole argument that straight weights are better because they "don't have VIIs" is no longer all that valid unless you're talking about low-end bargain oils.

Yes, you can be SURE that a straight 30 has no VIIs, and some modern synthetic straight 30s actually behave just like 5w30... but the very few VIIs it takes to make a 5w30 out of even Group II oils are pretty much insignificant. I'd say go with synthetic 5w30 if thats what your owners manual calls for. If you want to spend more for the very best- get Redline 5w30 or similar (no VIIs).

 

[aquariuscsm]

I`ve always wondered about straight weights...........say a SAE40 vs a 10W40/15W40 and an SAE50 vs a 20W50.

 

[tig1]

Running straight weight oil is something I did in the 60s. I used Valviline 20 wt in the winter and 30 wt in the summer. It worked well for me then, but that's old school. With the oils we have today( best I have seen in my many years of motoring) There is no need to do that.

 

[znode]

Originally Posted By: ledslinger

It seems to me that the advantages of running straight weight oils outweigh the disadvantages.


So viscosity is the only thing an engine needs to run 300kmi? Not having any antiwear agents, corrosion inhibitors, detergents, or dispersants "outweigh the disadvantages"?

I would like to have some of what you are smoking please.

 

[ThirdeYe]

Originally Posted By: znode
Originally Posted By: ledslinger

It seems to me that the advantages of running straight weight oils outweigh the disadvantages.


So viscosity is the only thing an engine needs to run 300kmi? Not having any antiwear agents, corrosion inhibitors, detergents, or dispersants "outweigh the disadvantages"?

I would like to have some of what you are smoking please.



Straight weights aren't always non detergent.

 

[tig1]

Originally Posted By: znode
Originally Posted By: ledslinger

It seems to me that the advantages of running straight weight oils outweigh the disadvantages.


So viscosity is the only thing an engine needs to run 300kmi? Not having any antiwear agents, corrosion inhibitors, detergents, or dispersants "outweigh the disadvantages"?

I would like to have some of what you are smoking please.



The straight wt oils I used in the 60s(valvoline) was "high detergent" oils, not non detergent.

 

[aquariuscsm]

I`ve considered a few straight weights........Valvoline VR1 SAE50,Royal Purple SAE40,and Royal Purple SAE50.

 

[d00df00d]

Originally Posted By: ledslinger
For summer use, over 50 degrees F, what are the pluses and negs of running a straight weight oil instead of a multi-visc?

All else equal:

The upside is better resistance to all forms of breakdown, better deposit control due to lack of VIIs, and possibly better wear protection.

The downside is maybe slightly worse cold flow, but not by much. If you're looking at a top-quality straight-weight, though, this won't be a big deal since most of them have high enough viscosity indices that they would qualify as multi-grades anyway, as BuickGN mentioned (his "straight-30" would qualify as a 10w-30).


Originally Posted By: ledslinger
Years ago I was told that BMW motorcycles specced straight weight oils partly because they have more lubricant since they have no VIs.

Important terminology point:

VI = Viscosity Index
VII = Viscosity Index Improver.

VI should be as HIGH as possible. VII content should be as LOW as possible.

Originally Posted By: ledslinger
Are we missing out on running more robust oils by avoiding stright weights in the summer?

Yes. But don't forget, if you keep switching between two oils, you won't get the full benefit of either unless the chemistries are very similar.


Originally Posted By: ledslinger
Unless these oils are considered outdated by the manufacturers and they don't use top quality ingredients or research.

Something like the opposite is the case. Many companies have oils that are marketed as straight weights even though they would qualify as multi-grades because the market for straight weights is alive and well.

 

[ledslinger]

The common straight weight oils I see are HDEO Rotella and Quaker State.

 

[znode]

Originally Posted By: znode

So viscosity is the only thing an engine needs to run 300kmi? Not having any antiwear agents, corrosion inhibitors, detergents, or dispersants "outweigh the disadvantages"?

I would like to have some of what you are smoking please.

Oh, in that case (quality fully-detergent straight weights vs multiweight), I apologize and retract my statement.

 

[ledslinger]

Important terminology point:

VI = Viscosity Index
VII = Viscosity Index Improver.

VI should be as HIGH as possible. VII content should be as LOW as possible.

Oops noted.

 

[d00df00d]

By the way, for what it's worth: A friend of mine runs RLI's straight SAE 30 in his Mini Cooper S, year-round in the NE US. RLI's oils have good enough cold characteristics that even their straight-30 is fine in winter, at least up here.

 

[BuickGN]

Originally Posted By: d00df00d
Originally Posted By: ledslinger
For summer use, over 50 degrees F, what are the pluses and negs of running a straight weight oil instead of a multi-visc?

All else equal:

The upside is better resistance to all forms of breakdown, better deposit control due to lack of VIIs, and possibly better wear protection.

The downside is maybe slightly worse cold flow, but not by much. If you're looking at a top-quality straight-weight, though, this won't be a big deal since most of them have high enough viscosity indices that they would qualify as multi-grades anyway, as BuickGN mentioned (his "straight-30" would qualify as a 10w-30).


Originally Posted By: ledslinger
Years ago I was told that BMW motorcycles specced straight weight oils partly because they have more lubricant since they have no VIs.

Important terminology point:

VI = Viscosity Index
VII = Viscosity Index Improver.

VI should be as HIGH as possible. VII content should be as LOW as possible.

Originally Posted By: ledslinger
Are we missing out on running more robust oils by avoiding stright weights in the summer?

Yes. But don't forget, if you keep switching between two oils, you won't get the full benefit of either unless the chemistries are very similar.


Originally Posted By: ledslinger
Unless these oils are considered outdated by the manufacturers and they don't use top quality ingredients or research.

Something like the opposite is the case. Many companies have oils that are marketed as straight weights even though they would qualify as multi-grades because the market for straight weights is alive and well.


Completely agreed.

I usually mention this but even though I run an expensive 30wt in my normal climate, I've gone to a 0w-20 in certain conditions. If your climate allows, a good straight weight that qualifies as a 10w or 5w is a great idea. After a certain cold cutoff point I'm sure the advantages of a multi-weight outweigh the advantages of a straight weight.

 

[addyguy]

I feel that with a quality base II oil or higher, most modern straight-30's are much closer to a '15W-30' than anyhting - just look at the pour points of most of them.

I see nothing wrong with running them when temps permit, which, given the above, is year-round in many areas.

 

[mechtech2]

Even in summer, you have to start a car.
And good flow is very important. A straight 50 is silly.
Not only too thick at starting, but at intermediate temperatures.