Multi-Vis: Why run a thinner "W" rated oil than recommended?

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paulo57509

paulo57509

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I was wondering about this the other day:

If a manufacturer recommends a 10w30, what is the reasoning behind running a less viscous W rating, such as an 0W-30?
 
The simple reason is when experiencing temperatures below -25C for which a 10W is rated. You would use a 5W for down to -30C and a 0W for temps down to -35C and below.
 
The 0-30 will give you higher cranking speeds when cold and will provide the fastest oil pressure. It will also give sightly better MPG as well. Its more of a winter/highway oil.
 
Well you would surely use it (or could use it) if you knew you had a shear stable 5w30. The only reason for a 10w30 spec is for the inherent shear stablility, IMHO.
 
A 0w30 will get oil to the bearings very quickly, just when you need it the most. I have been using Amsoil 0w30 for over 50K miles now and am pleased with it's performance. My highway gas mileage has gone from an average of 42.5 MPG to 48.8 MPG. (1993 Honda Civic, 1.5)
 
Call me stupid, but assuming you've run a xW-30 before running 0w-30, how would freeway mileage increase so dramatically? At normal operating temperature, isn't a 30 weight a 30 weight?
 
The reason I recommend a 0w30 over a 10w30 is that much of the time we operate with oil that has not fully warmed up. While water heats up to normal operating temperatures in 5 minutes, oil takes 15 to 20 minutes or longer.

At 70 F the 10w30 is much thicker than the 0w30 when starting up your engine. This taxes your starter more, oil flows slower and you get less HP from your engine. Because it took more effort to crank the starter, the battery was run down more so the alternator will have to run more and hotter. Parts wear out sooner because of these.

Both oils are the same thickness at operating temperature but our trips of less than half an hour cause the oil to run cooler and thicker. In my mind the fact that a 0W oil can start up at lower freezing temperatures is irrelevant for most people.

What is most important is that the 0W oil thickens less at 40 - 70 F than a 10W oil. This is where most people start up their engines.

aehaas

[ December 20, 2005, 06:28 PM: Message edited by: AEHaas ]
 
No, you're not stupid, I am only offering my you my actual experience. Originally I used Castrol GTX 5w30 Dino oil, after switching to Amsoil 0W-30, I recorded a solid improvement on MPG. I did a 3 thosand mile round trip to NY using the Castrol oil. I averaged 42.5 Mpg for that trip and burned 3 qts of oil. My last trip to NY, also 3K miles and using Amsoil 0W-30, The average MPG went up to 48.8 and I burned no oil!
 
When I started this thread, I didn't have low temperatures in mind. I suppose it was from reading about 0w-xx oils this past summer. So allow me to re-phrase.

All things being equal (temperature-wise), why would you want (or need) to run an 0w-xx over a 5w-xx or a 10w-xx if the manufacturer specifies a 5w-xx or 10w-xx is fine for a particular temperature?

Is there a point at which running an 0w-xx oil can be TOO thin for start-up conditions; again all things being equal?
 
From my oil chapters (not exact but show the point):

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

All oils including a straight 10 wt. oil are too thick at start up if the temperature is 75 F. As you go lower in temperature the difference is even greater.

aehaas
 
I believe the thicker the base oil the better, provided it is not too thick for startup. In a warm climate like I envison for California, you would run mostly straight 30 (Maxlife comes in SAE 30).
 
quote:
Oil type... Thickness at 75 F...Thickness at 212 F

Straight 30...... 250......................10
..10W-30..........100......................10
...0W-30...........40 ......................10
Click to expand...
How were these numbers determined?

I’m looking at the Pennzoil Platinum Full Synthetic product data sheet and it shows the following:

code:
SAE Grade cSt @ 40°C (~100°F) cSt @ 100°C (~212°F)





5W-20 46.84 – low 20 wgt 8.48 – high 20 wgt

5w30 59.66 – mid 20 wgt 10.52 – low 30 wgt

10W-30 63.23 – mid 20 wgt 10.37 – low 30 wgt
Click to expand...
Seems to me that if all of these grades have a lower viscosity at 100°F than they have at 212°F, it is going to be difficult for them to thicken as much as the quoted chart suggests with only a 25° drop in temperature.

Or am I reading the viscosity chart wrong?
 
quote:
The numbers are demonstrative and not from a single specific oil. The purpose was to answer the question asked above.
Click to expand...
If these numbers have no basis in fact, how can they answer the question?

I quoted some factual numbers from the manufacturer that suggest that at 100*F the stated oil is not as thick as it is at 212*F. A similar result obtains from a review of the specs for Castrol GTX 5W-20 and 10w30 oils. While I have not checked any other brand's PDS for this particular purpose, I can't help but think that a similar situation would generally exist with most quality oils if I am in fact reading the viscosity charts correctly.

I am just trying to ascertain what facts are relied on to contend that the hypothetical oil is thicker at 70*F than at 212*F?
 
Doyan, from what I could see the figures you posted showed an as-expected drop in viscosity with higher temp. How are you concluding that they showed the opposite?

ALL oils lose viscosity with temp, some more than others, and "grading" them into weight classes is helpful but arbitrary. I agree that with respect simply to viscosity, on a cold start at any ambient temp you would want the oil to be thinner than is possible, so all else equal (which it is not) you would want the lightest possible xW number.

- Glenn
 
As noted by AEHAAS, you really need to look at the viscosity of the particular oil you are considering. GC is thicker than almost all 5W30 oils and a lot of 10W30 oils even at cool temperatures. A high mileage 5W30 is thicker at all temps than most 10W30 oils. The weights on the bottles refer to viscosity at -25C and 100C.

It is helpfull to compare oils at typical startup temperatures for your application. My vehicles usually start up at 50 deg F in the winter and 60 deg F in the summer. GC would be thicker than most other 5W30 and 10W30 oils out there for my vehicles.
 
glennc and Winston, please look at the viscosity chart here: http://www.bobistheoilguy.com/visc.html

When it says that "viscosities can be related horizontially" I take it to mean from side to side, back and forth. If you will look at 10 cSt @ 100*C (210*F) it will relate to somewhere in the neighborhood of approximately 85 to 90 cSt @ 40*C (100*F). Both will yield SAE 30 weights, will they not? If 10 cSt @ 210*F is optimal operating viscosity then would not 85 to 90 cSt at 100*F be optimal operating viscosity? If an oil has a viscosity of 63 cSt @ 100*F would it not be thin enough at start-up if it was 100*F?

IF I AM READING THE CHART CORRECTLY, there is NOT a drop in viscosity from 100*F to 212*F but actually an increase on the stated oils. I will conceed that at some point as the temp gets lower the viscosity will increase but the stats for Penz and GTX suggest it does not happen from 212*F to 100*F IF the chart and accompanying statement are correct and IF the manufacturers data is correct. Does viscosity increase enough to make a difference when temp gets to 75*F or 60*F or 40*F? Maybe, but how does one go about determing without tests or factual data derived from tests?

Seems y'all are just making assumptions.
 
quote:
Or am I reading the viscosity chart wrong?
Click to expand...
No, you're interpretting the data wrong.

It's saying that @ 100F it appears as a 5w20 ..while it's still a 30 weight @ 212.

The viscosity at 100F is more like a 70 weight if it had that visc @ 212F

So at 100F ..you're pumping 70 weight oil (or somewhere in that range).

This is the main thrust of the good Dr.'s evangel. Most of us never reach our 100C/212F oil temp ..hence we are always (typically) pumping much heavier oil then is required to protect the engine. Hence is makes sense to get the thinnest oil (broadest VI) acceptable to reduce warmup visc.

But getting to Paulo's question. You can use anything that's a 30 weight (0w, or when they come up with it -50w) as long as you don't violate the reason that they spec'd the 10w in the first place ..which is because it has inherently more shear stability (off the shelf conventional oil) then a 5w over the duration of what they spec for an OCI.

You will reduce the parasitic losses due to unnecessarily higher viscosity in the warm up state.
 
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