Using M1 5w30 and 10w30 for my Subaru STi: should I switch to GC?

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So I've been using M1 5w-30 and now just changed to m1 10w30 for the summer months. I've heard a lot of great things about this magical GC that even has it's own sub-forum! Should I change it to GC? I have a Subaru WRX STi that has a turbo-charged 2.5L boxer engine. It sees single digit temps in the winter and 90+ degree in the summer. Here is my recent UOA:  - 1st UOA: Castrol GTX 5w30 2nd UOA: Castrol Syntec 10w30 3rd UOA: M1 5w30 I would love the input on all the GC fans here! Thanks!
 
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IF you can get some of the 04 batch (stamped M04XXXXXXXXXXXX) on the bottom I would surely give it a shot; then, if you don't get better results than with the M1, go back (I don't anticpate this happening). The reason I specify the 04 batch is that I recommend you go for the latest batch produced without going into 05 because that batch appears to be different than the previous batches and so is an unknown quantity. As an "Elfemeister," I intend to use it but I won't recommend an unknown to someone else. [Cheers!]
 

volkl23

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Thanks guys for your responses. I'm still quite a neophyte when it comes to oils so please bare with my questions [Smile] I understand M1 5w30 is quite thin. Is the GC thicker than the M1? Do you think the GC will be thick enough (compared to M1 10w30) to be effective in out hot STL summers (>90 temps)?
 
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quote:
Originally posted by volkl23: Thanks guys for your responses. I'm still quite a neophyte when it comes to oils so please bare with my questions [Smile] I understand M1 5w30 is quite thin. Is the GC thicker than the M1? Do you think the GC will be thick enough (compared to M1 10w30) to be effective in out hot STL summers (>90 temps)?
volkl23, The viscosity ratings for each grade are a scale not a single number (30W is from 9.3-12.5 cSt at 100ºC). As you can clearly see, GC at 12.1 cSt is on the "thicker end" of the 30W scale. M1 5W-30 and 10W-30 are both 10 cSt at 100ºC and so a the the "thinner end." So GC is thicker at operating temps than BOTH 5W-30 and 10W-30. You may be thinking, "How can a 0W-30 be thicker than a 10W-30?" This is a common area of confusion. The anwer is that the 0 and 10Ws refer to the weight when the oil is cold NOT when it is at operating temp. So to reiterate, if you want a thicker oil when your engine is at operating temps you want GC, NOT M1 10W-30.
 
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I still think that you could make a synergistic blend (marketting talk) of baby oil (cold pressed) and ear-wax and get a great UOA on a Subaru.
 

volkl23

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quote:
Originally posted by pscholte:
quote:
Originally posted by volkl23: Thanks guys for your responses. I'm still quite a neophyte when it comes to oils so please bare with my questions [Smile] I understand M1 5w30 is quite thin. Is the GC thicker than the M1? Do you think the GC will be thick enough (compared to M1 10w30) to be effective in out hot STL summers (>90 temps)?
volkl23, The viscosity ratings for each grade are a scale not a single number (30W is from 9.3-12.5 cSt at 100ºC). As you can clearly see, GC at 12.1 cSt is on the "thicker end" of the 30W scale. M1 5W-30 and 10W-30 are both 10 cSt at 100ºC and so a the the "thinner end." So GC is thicker at operating temps than BOTH 5W-30 and 10W-30. You may be thinking, "How can a 0W-30 be thicker than a 10W-30?" This is a common area of confusion. The anwer is that the 0 and 10Ws refer to the weight when the oil is cold NOT when it is at operating temp. So to reiterate, if you want a thicker oil when your engine is at operating temps you want GC, NOT M1 10W-30.

Thanks for your reply pscholte. Hmm... I didn't know M1 5w30 and 10w30 were so close in viscosity. I've been putting the 5w30 in the winter (single digit temps) and putting in the 10w30 in the summers. So do I even need to change to a thicker oil in the summer time? Also, do you think the the GC will be too "thick" for the cold winters? Wouldn't we want a thinner oil to go to all the moving parts of a cold engine ? LOL. Each answer I get results in me asking 5 more quetions! [Razz]
 
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quote:
Originally posted by Shannow: I still think that you could make a synergistic blend (marketting talk) of baby oil (cold pressed) and ear-wax and get a great UOA on a Subaru.
[LOL!] (Would you use Q-tips ear swabs to do an oil change)? [Big Grin]
 
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quote:
Originally posted by volkl23:
quote:
Originally posted by pscholte:
quote:
Originally posted by volkl23: Thanks guys for your responses. I'm still quite a neophyte when it comes to oils so please bare with my questions [Smile] I understand M1 5w30 is quite thin. Is the GC thicker than the M1? Do you think the GC will be thick enough (compared to M1 10w30) to be effective in out hot STL summers (>90 temps)?
volkl23, The viscosity ratings for each grade are a scale not a single number (30W is from 9.3-12.5 cSt at 100ºC). As you can clearly see, GC at 12.1 cSt is on the "thicker end" of the 30W scale. M1 5W-30 and 10W-30 are both 10 cSt at 100ºC and so a the the "thinner end." So GC is thicker at operating temps than BOTH 5W-30 and 10W-30. You may be thinking, "How can a 0W-30 be thicker than a 10W-30?" This is a common area of confusion. The anwer is that the 0 and 10Ws refer to the weight when the oil is cold NOT when it is at operating temp. So to reiterate, if you want a thicker oil when your engine is at operating temps you want GC, NOT M1 10W-30.

Thanks for your reply pscholte. Hmm... I didn't know M1 5w30 and 10w30 were so close in viscosity. I've been putting the 5w30 in the winter (single digit temps) and putting in the 10w30 in the summers. So do I even need to change to a thicker oil in the summer time? Also, do you think the the GC will be too "thick" for the cold winters? Wouldn't we want a thinner oil to go to all the moving parts of a cold engine ? LOL. Each answer I get results in me asking 5 more quetions! [Razz]

volkl23, Given that they are both 10cSt at operating temps, the 5W would not be any less protective than the 10W in hot operating conditions. What you do have to consider, though, given what Subaru recommends based on their engine testing, is the propensity of the oils to shear based on the natural viscosity index of the two versions and how much of the high end viscosity in the 5W is achieved through Viscosity Index improvers because of the wider viscosity spread. In regard to using GC in the winter...winter conditions are what it was actually designed for with its 0W when cold. It just so happens that with its 12.1 cSt when at operating temps it is also great for hot conditions. So look at it this way...it is thin at startup when you need it to be for quick flow to vital parts but it is thick enough to handle demanding conditions at the top end of the temperature scale.
 

volkl23

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pscholte: Looks like GC is a winner! Subaru recommends 5w30 all around, but GC seems to be perfect for our wild STL weather! I think I might give it a try at the next oil change. How does the GC compare to the thin M1 oils in terms of gas consumption? My car isn't exactly frugal with gas as it is. Will the higher cst affect my MPG. I could have sworn that I got a little bit better mileage from the 5w30 compared to the Castrol 10w30, but that could've been a placebo effect. Thanks again! [Cheers!]
 
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In a VOA posted by Stinky Peterson his test indicated M1 5-30 has an operating viscosity of 11.3 while the 10-30 tested 10.7. So in this case the 5-30 is actually a little thicker at operating temperature than the 10-30.Given the test variance from sample to sample it seems safe to say that based on these tests the average viscosity for both weights is around 11 which is just a little less than the GC.
 

volkl23

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quote:
Originally posted by SSDude: I'm a fan of GC. But, honestly, I don't if anything can impove this UOA. It looks pretty good.
An increase of 3mpg is great! Now I'm definetely leaning more towards the GC. One quick question... aren't thicker oils generally result in worse MPG? If the M1 is thinner than the GC at operating temps, how can the GC have a 3mpg improvement over M1? [Confused] Am I missing something blatant here? [Razz]
 
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quote:
Originally posted by farrarfan1: In a VOA posted by Stinky Peterson his test indicated M1 5-30 has an operating viscosity of 11.3 while the 10-30 tested 10.7. So in this case the 5-30 is actually a little thicker at operating temperature than the 10-30.Given the test variance from sample to sample it seems safe to say that based on these tests the average viscosity for both weights is around 11 which is just a little less than the GC.
I took the 10.0 numbers right from the Mobil Product Data Sheet so that is what Mobil says is the typical viscosity...could be old data not reflecting the latest product.
 
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quote:
Originally posted by volkl23:
quote:
Originally posted by SSDude: I'm a fan of GC. But, honestly, I don't if anything can impove this UOA. It looks pretty good.
An increase of 3mpg is great! Now I'm definetely leaning more towards the GC. One quick question... aren't thicker oils generally result in worse MPG? If the M1 is thinner than the GC at operating temps, how can the GC have a 3mpg improvement over M1? [Confused] Am I missing something blatant here? [Razz]

Please don't make a decision based on results in a different auto. I would love to see you using GC, but I want you to make that choice for the right reasons (e.g. test data, widespread performance patterns from a number of different automobiles on this board). In regard to your question, the answer lies in chemistry: friction modifiers, surface adhesion and flow characteristics of the oil...maybe Molakule will see this thread and add his considerable knowledge to the explanation...
 
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quote:
Originally posted by volkl23: pscholte: Looks like GC is a winner! Subaru recommends 5w30 all around, but GC seems to be perfect for our wild STL weather! I think I might give it a try at the next oil change. How does the GC compare to the thin M1 oils in terms of gas consumption? My car isn't exactly frugal with gas as it is. Will the higher cst affect my MPG. I could have sworn that I got a little bit better mileage from the 5w30 compared to the Castrol 10w30, but that could've been a placebo effect. Thanks again! [Cheers!]
volkl23, I'm getting about 3 mpg improvement with GC (city and highway) in a 3.0L Taurus. I have had only GC/SLX in the Audi since I first leased it so I cannot make a comparison there.
 
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