Advice from AutoHQ: Motor Oil
07-16-2008, 01:35 AM
#61
It's been a while since I've posted about oil... here goes 
"Sight" isn't a great indicator of how much life the oil has left or how well the oil is doing its job. The oil can be black but have plenty of life left and produce very low wear numbers.
More viscous oils produce more friction. (Maybe I'm over simplifying this?)
So how does a 20W-50 have less friction than the more common 5W-30s?
Wouldn't you want a thinner oil for cold start-up? It'll definitely flow better than a thicker oil.
With everything said, I do agree - very generally - that thicker oils do protect better in high stress situations. eg at the track.
-Thicker oils tend to withstand fuel dilution better, but ironically I recall they also cause more fuel dilution.
-They tend to have higher HTHS numbers (High Temperature High Shear) - which correlates to better protection in extreme situations.
Keep in mind there's some very convincing arguments for using "thin" oils too.
Anyways, there's always trade offs. A UOA is the most empirical method for determining what oil's right for you.
More viscous oils produce more friction. (Maybe I'm over simplifying this?)
So how does a 20W-50 have less friction than the more common 5W-30s?
The boxer engine requires thicker oil because of the relatively poor oiling of the boxer engine. The horizontal design (and gravity) is the cause.
Boxer engines tend to run out of oil film on the top due to gravity. And especially at cold start up the piston skirt is lying on and in contact with the bottom/lower cylinder wall.
Boxer engines tend to run out of oil film on the top due to gravity. And especially at cold start up the piston skirt is lying on and in contact with the bottom/lower cylinder wall.
With everything said, I do agree - very generally - that thicker oils do protect better in high stress situations. eg at the track.
-Thicker oils tend to withstand fuel dilution better, but ironically I recall they also cause more fuel dilution.
-They tend to have higher HTHS numbers (High Temperature High Shear) - which correlates to better protection in extreme situations.
Keep in mind there's some very convincing arguments for using "thin" oils too.
Anyways, there's always trade offs. A UOA is the most empirical method for determining what oil's right for you.
07-16-2008, 02:31 AM
#63
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**In Dave Chappells white man nerdy voice**
"All you sons uh *****es! I will NOT stand for such actions!"
My argument is not on the weight, it is on the mile increments in which you change the oil at. To say it is necessary to change the oil every 1500-2000 miles on a NORMAL wrx or sti is absolutely retarded. Again certain factors apply to that statement; how hard you drive, temperatures you commonly drive in, and how often you track the car which can go under the how hard you drive category.
And the manual suggests the heavier weight in the more "extreme" conditions. Sure you don't need to wait until extreme conditions (my term for extreme being 85+ F) to run a heavier viscosity.. but point being you don't NEED to run the heavier weight like said in the OP.. The graph shows you can run the lower viscosity and higher viscosity in warmer to hotter temps.
So you saying we are trampling on an "otherwise informative" thread is about as exaggerated as a wild claim made by a shop trying to score more oil change business. There was no informative info in this thread....
That is until I posted
Last edited by evsoul; 07-16-2008 at 02:34 AM.
07-16-2008, 05:22 AM
#64
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Anyone concerned about OCI's should have an oil sample analyzed by blackstone labs - that is the only way to truly know whats going on with the oil. There are MANY highly modified turbo subarus running over 5K miles on a single OCI that have excellent oil analysis - Some even run them up to 7K with great results (bluesubie on nasioc)
www.bobistheoilguy.com
www.bobistheoilguy.com
German Castrol (GC) FTW!
http://www.bobistheoilguy.com/forums...643#Post718643
07-16-2008, 07:19 AM
#65
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brandon never requested that anyone go to his shop for an oil change, and as far as I can tell, he was pretty clear that the aggressive change schedule is for a very aggressive driving style and setup. If you run at, close to, or in excess of 1.5 bar of boost, this would become much more pertinent. But then, how many people in here are actually running that? I know I'm not, but that doesn't mean you can go and discount everything he says.
<----------- still using stock turbo
<----------- still using stock turbo
07-16-2008, 08:32 AM
#66
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I even went ahead and highlighted the pertinent parts for you guys, so you don't have to read through a whole 2.5 page article
This is from a shop manual for a USDM 2004 STi, from subaru.
So, we can all agree that we do not live in the arctic right? Because alaska is part of the US. Here's a shout out to our subie boys who SHOULD be rocking 5w-30
For the rest of us mojito sipping bay area denizens, if you drive a stock turbo subaru non-aggressively, and do not track or auto-x, you should be using 10w40. Now that's a surprise. But hey, it's right there in the shop manual.
So let's say you are the average I-clubber. I'd say that description fits us all pretty well, right? You have probably modified your car. Probably. Also, you probably drive your car harder than the average soccer mom. Probably. You guys still with me here?
OK, next point. In the subaru manual, and using common sense, the harder a car is driven, or the more heavily modified (subaru does not address this, but we are going to go ahead and presume that modifying the car will cause higher levels of wear. This is very non-technical, we are trying to keep this simple) You should then be using a STILL THICKER OIL. Subaru even recommends a few viscosities. INCLUDING 20w50!!!!!
Did that totally blow your mind? I'm going to have a cigarette, I'm spent.
So to sum it up, the answer isn't at AutoHQ, or anywhere in this thread. It is in the shop manual for your car, had you bothered to read it.
I hear the real estate market in Alaska is fantastic this time of year.
and people you are pissed off at DO recommend 15w when tracking your car, and changing that oil more often.
Spirited driving does NOT fall under the condition of a NEED or compulsion to run 15w or heavier oil.
I Highly doubt Kevin feels the same as Brandon.
07-16-2008, 09:12 AM
#70
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+1, if you are really serious about your oil concerns have it analyzed after an oil change. Best way to determine what's going on with YOUR engine.
German Castrol (GC) FTW!
http://www.bobistheoilguy.com/forums...643#Post718643
German Castrol (GC) FTW!
http://www.bobistheoilguy.com/forums...643#Post718643
GC ftw!
07-16-2008, 09:17 AM
#71
I buy it in hoardes because there is only one autozone in my area that sells it.
07-16-2008, 09:20 AM
#72
I most agree with Mike from GST with his general recommendation of 3K and 10W something. This schedule will work great for almost everyone.
I am no oil expert, not even close. I posted this thread to share information from Subaru and encourage people to take care of their cars.
So I have a great appreciation for these cars, and it's why I hate to see one with any damage because of irregular maintenance.
I am no oil expert, not even close. I posted this thread to share information from Subaru and encourage people to take care of their cars.
So I have a great appreciation for these cars, and it's why I hate to see one with any damage because of irregular maintenance.
Last edited by AutoHQ; 07-16-2008 at 06:04 PM.
07-16-2008, 09:23 AM
#74
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....
However in our cars we get very similar mileage per tank (about 280 mph daily driving) using 20W-50. Thicker oil is about the same price (comparing Mobil 1 5W-30 to 15W-50), and protects the engine better.
Many dealerships are putting 10W-30 oil in almost every car coming through the door because it is able to be used universally, or almost so, in many different engines, and it is cheaper and more convenient to stock one kind of oil than many.
......
Brandon
However in our cars we get very similar mileage per tank (about 280 mph daily driving) using 20W-50. Thicker oil is about the same price (comparing Mobil 1 5W-30 to 15W-50), and protects the engine better.
Many dealerships are putting 10W-30 oil in almost every car coming through the door because it is able to be used universally, or almost so, in many different engines, and it is cheaper and more convenient to stock one kind of oil than many.
......
Brandon