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post #1 of 34 (permalink) Old 07-15-2009, 09:19 AM Thread Starter
 
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10W40 or 0W40???

LIving in Texas we have had 20+ days over 100F this summer. I am changing to 10W40 Castrol Syntech... I feel it will handle the heat better than the European 0W40.. Has anyone else changed from Mobil 1 0W40??? Your thoughts.
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post #2 of 34 (permalink) Old 07-15-2009, 09:29 AM
 
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You should be okay in Texas, cold starts should be rare for you, but there probably won't be a diffrence. I'd stick to 0W-40
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post #3 of 34 (permalink) Old 07-15-2009, 10:26 AM
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My '08 smart never had Mobil 1 0W-40. It did go 65 miles on the Mitsu engine factory's unknown fossil oil, then a 5W-30 ever since. My smart center in SE VA uses Castrol Syntec 5W-30. The 40-weight will do you more good in Texas than the 0W-.

Check your OpMan for smart's recommendtions on choosing the proper oil viscosity (it is in the new '09 manual).
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post #4 of 34 (permalink) Old 07-15-2009, 12:44 PM
 
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Simply stated...
The first number is a tested viscosity rating at cold temps. The thinner the oil is for starting a cold engine the better - and that is regardless of ambient temperatures. A 0W-40 oil is a much better alternative than a 10W-40 oil.

The second number is the tested viscosity rating at operating temps (ignoring the precise testing parameters). It is the significant number for your ambient temperatures and engine operating parameters.

All other considerations aside - the OW-40 oil is a superior blend to the 10W-40 oil. It is a mistake to think you are better off with the 10W-40 blend - you are most definitely not better off with that oil!

For generally knowledgable and reliable information on oils and related technologies go to bobistheoilguy forums.
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post #5 of 34 (permalink) Old 07-15-2009, 09:51 PM
 
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FWIW...

The first number (the "5" in 5w30) is only a relative number which basically indicates how easily it will
allow an engine to "turn over" at low temperatures. It is NOT a viscosity reference. In other words, a
10w30 is NOT a 10 weight oil in cold temperatures and a 30 weight oil in warm temperatures.
In fact, since SAE viscosity classifications only apply to an oil at 100 degrees C, it doesn't even make
sense to label it as a certain SAE viscosity at any temperature other than 100 degrees C.
Besides, if you thought about it for a second, it wouldn't make sense for a 10w30 oil to be a 10 weight
oil in the cold and a 30 weight oil in warm temperatures. What liquid do you know of that gets "thicker"
as its temperature increases or "thinner" as the temperature decreases?
I would venture to say you probably can't come up with one. This holds true for motor oil as well. If a
10w30 was a 30 weight oil at 100 degrees C and a 10 weight oil at cold temperatures, that would mean
it "thinned out" as the temperature dropped. That just doesn't make any sense considering what we
know about liquids. It just doesn't happen like that.
The fact is that a 5w30 motor oil is thicker in cold temperatures than in warm temperatures. However,
a 5w30 motor oil will be thinner than a 10w30 motor oil when subjected to the same low temperature
conditions - because the "W" number is lower. This is an indication of better cold weather performance.
In other words, a 5w30 flows better in cold weather than a 10w30 motor oil will. Think of the "W" as a
"winter" classification instead of a "weight" classification.
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post #6 of 34 (permalink) Old 07-16-2009, 12:53 AM
 
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Quote:
Originally Posted by lebikerboy View Post
FWIW...

The first number (the "5" in 5w30) is only a relative number which basically indicates how easily it will
allow an engine to "turn over" at low temperatures. It is NOT a viscosity reference. In other words, a
10w30 is NOT a 10 weight oil in cold temperatures and a 30 weight oil in warm temperatures.
In fact, since SAE viscosity classifications only apply to an oil at 100 degrees C, it doesn't even make
sense to label it as a certain SAE viscosity at any temperature other than 100 degrees C.
Besides, if you thought about it for a second, it wouldn't make sense for a 10w30 oil to be a 10 weight
oil in the cold and a 30 weight oil in warm temperatures. What liquid do you know of that gets "thicker"
as its temperature increases or "thinner" as the temperature decreases?

You really need to do a little more research on oil technology and how oils are rated and by whom.

Multigrade oils are tested and certified to have a specific rating at two different temperatures - -18 centigrade for it's cold rating, and 100 degrees centigrade for it's hot rating.
The designation 5W-30 means that the oil was tested to flow as a 5 weight single grade oil at -18 degrees C. The "W" does stand for "Winter". It does not stand for weight.
That same multigrade was also certified to flow as a 30 weight single grade oil at the hot temperature. This does not mean that it is thicker when hot than it was when cold. It isn't. All oils thin as they are heated and that includes multigrade oils. A Viscosity Index Improver is added to standard base oils to prevent them from thinning as much as they would otherwise. This allows them to behave as a thin oil at cold temps and as a thicker oil would when heated to a higher temperature.
Synthetic oils behave a little differently and don't require VI improvers.

That's the simple explanation. I can't be bothered to go into any more detail here now - for something a little more technical see http://www.carbibles.com/viscosity.html
Here's another one - http://mysite.verizon.net/oldhokie/windyridge/oil.pdf

You might also want to investigate rating systems and specifications for different oils to see how they compare.

Also, if you still doubt what I've said then why not try posting what you did here at the bobistheoilguy forums and see how they respond? Those forums are populated by many tribologists and other petroleum experts and interested individuals. http://www.bobistheoilguy.com/
Here's a little bit of general information from that site. http://www.bobistheoilguy.com/oildefinitions.html
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post #7 of 34 (permalink) Old 07-16-2009, 07:32 AM
 
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And you may want to read this...

http://www.zag.si/~jank/public/bmw/oil_bible.pdf
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post #8 of 34 (permalink) Old 07-16-2009, 07:35 AM
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See folks, this is how disagreements should be handled - the Canadian way.
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post #9 of 34 (permalink) Old 07-16-2009, 07:38 AM
 
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Quote:
Originally Posted by fortow View Post
You really need to do a little more research on oil technology and how oils are rated and by whom.
Not to sound rude, but you should also do some reading on your own before criticising other peoples' information. Your statements on viscosity are not accurate and several of your comments contradict themselves.

Take a look at the file that lebikerboy posted and you'll find all of the (correct) information you need.
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post #10 of 34 (permalink) Old 07-16-2009, 07:48 AM
 
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posted before...doing it again...
Introduction to Motor Oil

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