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Old 01-30-2005, 10:45 PM   #1
Silver04WRX
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Default Motor Oil Questions

I've been trying to figure out which oil weight would be best for me. I understand that 5W-30 is preferred, but I also saw in the manual that heavier weights may be better suited for some drivers.

Ok, so what is the difference between 5W30 and 10W30? I know that the two oils have the same summer rating (is that the right word??), but what I want to know is how much of a difference there is between the 5 and 10 winter rating. People have said that gas mileage would go down....how much of a difference would there be? If the summer ratings are the same and the winters are different, wouldn't these oils be extremely similar? I mean, the difference between using one or the other would be rather small.

Maybe this will make things easier...the coldest temps I see in the winter are 20 degrees F and the hottest in the summer are about 90 degree F. Should I run different weights in summer and winter?

Thanks.
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Old 01-31-2005, 11:06 AM   #2
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Ok....went to the Mobil1 website to look at the specs

Grade | 5W30 | 10W30
cSt@40 deg C | 56 | 62
cSt@100 deg C | 10 | 10
Viscosity Index | 167 | 147
Sulfated Ash | 1.2 | 1.2
HTHS Viscosity | 3.08 | 3.17
Pour Point deg C | -45 | -45
Flash Point deg C | 224 | 244
Density 15 deg C | .861 | .872

Can someone help me out with these numbers? Aren't they really similar? How can they have the same summer rating if one if thicker?

Also...are these oils new:
http://www.mobiloil.com/USA-English/...Oils/Oils.aspx

The extended performance, clean 7500, and clean 5000? Anyone try the extended performance?
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Old 01-31-2005, 11:56 AM   #3
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Those numbers don't refer to summer and winter. It's a rating of the oil's viscosity at cold temperature vs warm temperature. If you put Xw30 in your engine, it's still going to 'act' like a 30 weight oil when it warms up, no matter what the first number is. It also has no bearing on what the outside temperature is, either. Your car is going to run somewhere around 175 degrees (ballpark) weather it's -10 degrees or 120 degrees out there.

5w30 is the recommended grade for our cars for the average daily driver in most conditions. If you live where it gets real cold overnight and your valvetrain sounds like an old sewing machine for a few minutes after you start it up, you could try something like 0w30 for the winter. If you live in Arizona in August, something ending with a 40 might be better, especially if you're hard on your car. Follow?

Generally, you can't go wrong with the recommended weight unless your location or driving habits dictate a change.
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Old 01-31-2005, 03:06 PM   #4
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That makes sense...but what I'm really trying to understand is the difference between the 5w and 10w since they both have the same warm rating. How much of a difference is there between the two? I've been using Mobil 1 5W30 and people say that it is one of the thinner 5W30s. People say 10W30 is thicker, which I understand...but why would they have the same warm rating (if the 10W30 is thicker than the 5W30)?
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Old 01-31-2005, 03:29 PM   #5
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The 5 is thinner then the 10. The 30 is the same which is why it has the same "warm" rating. The 5 is better all around I think especially for people like me who live in colder climes-

FWIW

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Old 01-31-2005, 03:47 PM   #6
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Besides pour point, and I hope it never is so cold that oil gels, there are some standard guides to go by. I was given a handbook called "AutoRef," and here is what it says. Take the coldest temperature your car will experience. Check the lows in your area.

-20 F can't use 20w20, 20w40, 20w50, 10w30,10w40,10w, but you can use 5w30 ,5w20

0 F you can use 10w30, 10w40, 10w, 5w30, 5w20

20 F you can use any listed except 5w20

If the lowest outside temperature is 80 F or 100 F it would be better to
use 10w30 than 5w30. 60 F would be a toss up.

I have always used 5w30 year round in about a dozen cars I own or have owned. Some of these cars fell apart before the engines started burning Mobil 1 5w-30. However, I don't live near hell either.*

*The book says in the footnote
"Manufacturer's specs should always take precedence over the tables."
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Old 01-31-2005, 04:12 PM   #7
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z&cobb - thanks, that helps.

The thing I've found from searching is that people think you can ONLY use 5W30...but the manual also gives other oils for different applications. I've also found from searching that it is best to have the two numbers closer together - as in 5W30 is better than 5W40...I don't know why though.

What I'm still trying to figure out is the difference between the 5 and 10? How much of a difference is there?? It seems like 10W30 would work for me all year around. I run from 20 deg F to 90 deg F. It's hard to understand oils from searching....people make 10W30 seem like it is super thick.
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Old 01-31-2005, 11:09 PM   #8
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Quote:
Originally Posted by Silver04WRX
z&cobb - thanks, that helps.

The thing I've found from searching is that people think you can ONLY use 5W30...but the manual also gives other oils for different applications. I've also found from searching that it is best to have the two numbers closer together - as in 5W30 is better than 5W40...I don't know why though.

What I'm still trying to figure out is the difference between the 5 and 10? How much of a difference is there?? It seems like 10W30 would work for me all year around. I run from 20 deg F to 90 deg F. It's hard to understand oils from searching....people make 10W30 seem like it is super thick.
In my case early morning temperatures can be about 0 to 5 F, and I have a 15.9 lb battery. I go out and spin up the fuel pump, turn on the starter and the engine starts instantly with little battery drain. The 5w-30 flows freely, so the lubrication of critical parts goes easily. I will try to find my Lubricants book, and find viscosities for 0, 5, 10 and 15w's at some low temperature.
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Old 01-31-2005, 11:59 PM   #9
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Skipping a lot of stuff about the use of viscometers to measure the flow rate of oils, there is a simple explanation of the 5w and 30 numbers.

Viscometers measure time (seconds) for a standard amount of oil to flow out of viscometer bulb through a defined tube, at a predetermined selected temperature.

Under these classifications, the winter grades of 5W, 10W and 20W are determined by the oils' viscosity at 0 Fahrenheit (-18C), while grades 20,30, 40 and 50 are determined by its viscosity at 212 Fahrenheit (100C). Those are the predetermined temperatures. The numbers are comparable within the same set, W and Summer. W = winter, the 0 F test, the other number is the time at the bp of water, 212 F. The two viscometers need not have the same orifices, or whatever, so don't try to relate the W set with the summer set.

So, 5W flows twice as fast as 10W at 0 F, and 20 flows twice as fast as 40 at 212 F.

Here's where some some confusion can exist when the oil is 0W, implying zero seconds out of the bulb. That is impossible. 0W is a special case denoting a difference in the 'pour point' of the oil. Most 5W oils have a pour point at -40F (-40C) The base oil is the same in 0W40, but it's pour point has been lowered even further - sometimes to as much as -50F (-46C). Pour point is important in extremely cold areas. Put a beaker of oil on a block of dry ice and won't pour at all.

An oil to do everything has to have more additives than one that doesn't have to do everything. So, it's best to use 5w30 than 5w40, at least in the minds of people who are thinking about additive levels diluting the "real oil."

Engines are not as simple as viscometers, so what it says in the Manual is important.

The chart on Page PM-5 of Vol 1 (2002 Model year) says,

10w30 and 10w-40 are OK from -4 F to over 104 F, and
5W-30 is "preferred" from below -22 F to 104 F.

For desert areas or heavy duty applications you can use
API classification SJ or SH, SAE Viscosity No.
30, 40, 10w50, 20w40, 20w50, it notes on the same page.

I don't want to use any of those. I have spent a few weeks in
the high desert Navy and Army sites near La La land. You have
to travel with bottles of water to stay hydrated. 40 would
work there, forget the W.
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Old 02-01-2005, 12:18 AM   #10
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z&cobb....thank you. That pretty much answers all my questions.

I guess I'll use 5W30 in the winter for better flow and 10W30 in the summer months.
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Old 02-01-2005, 08:41 AM   #11
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Quote:
Originally Posted by Silver04WRX
I guess I'll use 5W30 in the winter for better flow and 10W30 in the summer months.
Okay, but again, there really is no reason to put in an oil that's thicker than 5w in the summer. All you're going to to is make the oiling system work a little bit harder, taking a bit longer for it to get oil to everything during a cold start up. And you're still going to end up with a 30w oil when it's warm anyway, so there's no reason to do what you're saying. If 30w oil works for your climate and driving habits, just stick with 5w30 all year.
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Old 02-01-2005, 10:02 AM   #12
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Quote:
Originally Posted by Bottom Feeder
Okay, but again, there really is no reason to put in an oil that's thicker than 5w in the summer.
Sure there is. Even though the 5w and 10w are the same thickness at 100C, the 10w has a higher High Temp High Shear viscosity. The 10w should shear down less than the 5w.

Quote:
Originally Posted by Silver04WRX
I've been using Mobil 1 5W30 and people say that it is one of the thinner 5W30s.
That is correct. The SAE has a minimum and maximum range for each weight of oil. M1 30 weights are on the lower end of that range. I'm currently using German Syntec 0W30 which is actually thicker at 100C than any of the M1 30 weights.

There's the camp that believes that thicker is better, then there's the camp that believes thinner is better. Do a used oil analysis comparing two weights and you can see which one performs better for you.

-Dennis
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Old 02-01-2005, 10:26 AM   #13
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Quote:
Originally Posted by bluesubie
Even though the 5w and 10w are the same thickness at 100C, the 10w has a higher High Temp High Shear viscosity. The 10w should shear down less than the 5w.
True, but the difference is marginal. Going by those numbers, I think having a thinner oil at cold temps like 5w30 that protects better against the wear that you know will happen on a cold start is a better idea than a similar warm-temp grade like 10w30 that might protect better at a temp that a street car shouldn't really be seeing (212 degrees F) anyway.

As they say, most of an engine's wear happens at startup. Anything you can do to protect it during the first few minutes after a cold start is in its best interest.
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Old 02-01-2005, 11:21 AM   #14
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Quote:
Originally Posted by Bottom Feeder
True, but the difference is marginal.
Yeah, maybe. After ~5,500 miles in a Rex with M1 10W30, my viscosity was down to 9.95. The viscosity under similar mileage on my FXT with M1 5W30 was 9.58. The minimum thickness for a 30 weight is 9.3. The FXT probably saw higher revs than the Rex too.

-Dennis
p.s. - I don't think oil temps of 212F temps are that unusual, especially in 90F weather.

Last edited by bluesubie; 02-01-2005 at 12:07 PM.
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Old 02-01-2005, 11:31 AM   #15
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Mobil1 5/30 is significantly less shear stable than most other oils, including 10/30. Go to www.bobistheoilguy.com and see actual proof of that in the UOA section.

My TS burned 5/30 like a mofo. I am now using german Castrol 0/30 and with 6000 on the odometer have not burned a drop.

Next I will try Mobil 1 Truck & SUV 5/40.
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Old 02-01-2005, 05:25 PM   #16
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Ok...I'm kind of confused again. I was thinking that 10w30 would be better because the numbers are closer together and it would be better in the summer. I tend to burn somewhere around half a quart between oil changes with Mobil1 5W30.

Speaking of numbers being close together....why do some VWs use 5W40? When people say the numbers should be close together, how far do the number have to be to be an issue?
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Old 02-01-2005, 06:50 PM   #17
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yes run different oil because in the winter the oil gets thicker and you need thinner oil and in the summer the oil gets thinner and you need thicker oil like run 5w30 in the winter and 10w30 or 10w40
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Old 02-02-2005, 09:36 AM   #18
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From what I've read on bobistheoilguy, using an oil because the numbers are closer together is more old school thinking. Several years ago, the added viscosity improvers would burn up and hose up your engine. Synthetics have changed a lot over the years and the formulas are constantly changing and the viscosity improvers are much better.

If you're burning oil, I believe that a thicker oil (not necessarily an oil with a close viscosity spread) would cause you to burn less because it's more shear stable. That's why I mentioned above that you should also look at the HTHS number. The higher the number, the less the oil should shear down and/or burn. Besides those numbers, you also have to look at base stocks, virgin oil analysis', used oil analysis' to really get an idea of how an oil will perform. And don't always go by what's on the bottle or what some people say about weights. German Castrol Syntec 0W30 is thicker than M1 10W30. An oil doesn't have to be thinner to get the 0. It just has to be able to flow better in lower temps. M1's 0W30 is thicker at operating temp than the 10W30, although I believe it has a lower HTHS.

I highly recommend checking out the forums at BITOG .
Do some poking around in Car and Truck Engine oil for general info, and the UOA and VOA forums.

Hopefully my post is accurate and makes a little sense. I haven't finished my morning coffee yet.

-Dennis
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Old 02-02-2005, 10:49 AM   #19
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bluesubie -
That makes sense about the old school thinking, but then why don't people use 5W40 or 0W40 or similar oils more often? I'm not doubting you. I know VWs use 5W40. Why can't we?

I know Mobil 1 0W40 has a higher HTHS number than 5W30 and 10W30....so why shouldn't I use that?

Thanks for your help!
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Old 02-02-2005, 12:34 PM   #20
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Shearing is time/mechanical/chemical dependant. I don't drive easy steady state (like Interstate) and I have a txs utec stage 3 95 octane, so I use the oil as a "cleaning" agent and non-power robbing lubricant, and get rid of it at 3000 miles. It seems to work for me and the engine is "oil tight" at 78,000 miles despite power abuse and driving abuse. Perhaps my car was just built well?

It is possible that my wrx experience falls under the upper quartile of the Gaussian distribution of fortune. Maybe this is why I can just follow the KISS* concept.

The opposite of KISS is MICE*

*Make it complicated expert
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Old 02-02-2005, 01:04 PM   #21
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Quote:
Originally Posted by Silver04WRX
bluesubie -
That makes sense about the old school thinking, but then why don't people use 5W40 or 0W40 or similar oils more often? I'm not doubting you. I know VWs use 5W40. Why can't we?

I know Mobil 1 0W40 has a higher HTHS number than 5W30 and 10W30....so why shouldn't I use that?

Thanks for your help!
Fuel economy!

If you check the temp. chart in your owner's manual, you'll see that it shows 5W30, 10W30 and 10W40 with 5W30 being "preferred". It also says "Engine oil viscosity (thickness) affects fuel economy. Oils of a lower viscosity provide better fuel economy. However, in hot weather, oil of a higher viscosity is required to properly lubricate the engine." I think people stick with 5W30 because that's what's on the cap. More STi owners are starting to use M1 0W40 if you check the 2.5T technical forum.

As for VW, maybe they're just more forward thinking with oil. Europeans get better oils. That's why the hard to find "GC" (German Castrol Syntec) is so popular on bobistheoilguy.com. The formula that's made in germany is better than the one made in N. America.

Over on Subaruforester.com, the Brits laugh at us for using 5W30. Like poison mentioned above, I'm thinking of going with M1 T&SUV 5W40 this summer.

-Dennis
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Old 02-02-2005, 01:59 PM   #22
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I've been running Valvoline Synpower 5w-40 since 1999 in VWs, Audi's, Subies, Nissans and Volvos.
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Old 02-02-2005, 02:50 PM   #23
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When people say fuel economy will go down....by how much will it go down? For example, from a 30 weight to a 40 weight? I'm thinking about doing 5W40 or 0W40 in the summer. If synthetic oils are so much better now, why would anyone use 5W40 over 0W40? Just curious. Thanks for putting up with my lack of knowledge on this subject....
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Old 02-02-2005, 03:40 PM   #24
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My head is going to explode.
You haven't search around on bobistheoilguy yet, have you?

From what I've read, fuel economy probably varies by 2-4 mpg's. 2 mpg's is very important to a company like Subaru, who is skating on thin ice to meet the minimum mpg requirements (CAFE). A 5W40 is going to be thicker than a 0W40. For M1 it's 14.3 vs 14.8 cst's at 100C.

-Dennis
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Old 02-02-2005, 04:54 PM   #25
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Quote:
Originally Posted by bluesubie
My head is going to explode.
You haven't search around on bobistheoilguy yet, have you?

From what I've read, fuel economy probably varies by 2-4 mpg's. 2 mpg's is very important to a company like Subaru, who is skating on thin ice to meet the minimum mpg requirements (CAFE). A 5W40 is going to be thicker than a 0W40. For M1 it's 14.3 vs 14.8 cst's at 100C.

-Dennis
Yeah...I took a quick look at bobistheoilguy....and by quick look, I mean I didn't look at all . Sorry.

So, what's with Mobil1 truck and SUV 5W40? Why do they have to specify truck and suv?

I'm leaning towards Mobil1 5W30 synthetic in the winter and probably Castrol Syntec 5W40 in the summer. How's that for a final answer??
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