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Old 05-26-2003, 02:25 AM   #1
yayitzian
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Default 5w30 or 10w30

i'm running almos 18K miles now, and about to get an oil change.
im running on synthetic now, have been since 12000 miles. so my question is 5w30 or 10w30? some people say 10w30 is too thick for my car, but i run it hard a lot of times.

also, a reliable brand would be nice too. thanks
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Old 05-26-2003, 07:48 AM   #2
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10w-30 is still a 30 weight oil, so it isn't thicker at operating temperature, only a little thicker at startup when it's cold. Why would you want the oil to be thicker when you're starting the engine in your $25k turbocharged car?
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Old 05-26-2003, 08:49 AM   #3
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If you look at the owners manual, it lists what oils you can use at what ambient temperatures - this time of year, either one is fine. (so I suppose the answer to your question is that it doesn't matter)

for a multi-viscosity oil, the first number is the viscosity when cold, and the second when hot - so a 10w30 is as thick as a 10 weight when cold, but at temperature it's viscosity only drops down to what a 30w oil would be - so the only difference (functionally) between the two is that the 5W30 will be thinner when you start the car - the two will be more or less the same at temperature.
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Old 05-26-2003, 09:22 AM   #4
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Quote:
so a 10w30 is as thick as a 10 weight when cold, but at temperature it's viscosity only drops down to what a 30w oil would be - so the only difference (functionally) between the two is that the 5W30 will be thinner when you start the car - the two will be more or less the same at temperature
Exactly. I take it your in San Jose, California? If so, 10w30, which the manual calls for, is probably best for you. For colder climates, say like, below 20 F in the winter time, I would choose 5w30 even though 10w30 would suffice. From my experience with my last car ('89 Probe), running 5w30 in the winter time helped my lifter peck and also started easier on those frosty mornings.

-Charles-
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Old 05-26-2003, 12:46 PM   #5
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san jose in the summer, riverside in the rest of the year
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Old 05-26-2003, 01:39 PM   #6
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You can use either (Subaru "recommends" the 5w30 for fuel efficiency reasons); since you're on the warmer end of things, I would probably go with 10w30 Mobil 1.
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Old 05-26-2003, 02:10 PM   #7
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Subaru "recommends" the 5w30 for fuel efficiency reasons
5w30 doesn't make the engine work as hard during cold start-up, thus, reducing friction and effort needed to run the engine. I think the "efficiency" Subaru is talking about is the 1% better gas mileage you get by using 5w30. I know on Fords 5w30 yeilds better gas mileage, I assume the same goes for Subaru. The difference isn't really noticeable and can be negated through driving habits.

-Charles-
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Old 06-05-2003, 12:29 AM   #8
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I've been running Mobile 1 15W-50. It claims it intended for high revving and turbocharged engines. I used it for the last 3000 mi and had no starting problems whatsoever. I really can't feel any difference but as stated I've had no problems and it's been a chilly spring so far here. I think I am going to try a 10w to see if there's a noticeable difference. Winters here are a different story. I definitely go with the 5w.
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Old 06-05-2003, 12:52 PM   #9
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Quote:
Originally posted by TyranosaurusWRX
I've been running Mobile 1 15W-50. It claims it intended for high revving and turbocharged engines.
You are making the oil pump work harder than it needs to (30w vs 50w) with the result of REDUCING the effectiveness of the lubrication system and reducing the power of the engine.

With engine lubricants, you want to run the thinnest that will do the job. The mfr recommendations trump the oil company marketing blurbs. Subaru warranties the auto, not Mobil. If you doubt me, try getting Mobil to pay for engine repairs.
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Old 07-02-2003, 12:33 AM   #10
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I too have been using the Mobil 1 15W50 and haven't had any problems , but if it is causing a problem it probably won't show up until it is too late now that i think about it. I am probably going to change to 10W30, but I am thinking maybe i should stick with that oil because i am getting a VF34 upgrade this week and i drive in sunny so. california --- Help!
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Old 07-02-2003, 05:39 AM   #11
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Quote:
Originally posted by Bluewrx12
I too have been using the Mobil 1 15W50 and haven't had any problems , but if it is causing a problem it probably won't show up until it is too late now that i think about it. I am probably going to change to 10W30, but I am thinking maybe i should stick with that oil because i am getting a VF34 upgrade this week and i drive in sunny so. california --- Help!
I would go back to 10w30. 15w50 sounds like it would be the best stuff, and a few people mentioned it is actually recommended overseas, but doing some searching around on redline, mobil1, and amsoil websites I don't think it's a good fit. The only one that gave some good details besides the "great for supercharged and turbo cars and aggressive driving..." was the redline site, and it gave oil temperature ranges for their 10w40 and 15w50 oils. Can't remember off the top of my head and my dial up is way too slow right now, but I do remember that the temp recommended to use 10w40 was higher than I have peaked at with my GReddy temp gauge (somewhere in the 210F+ range), and 15w50's temp was much higher.
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Old 07-02-2003, 10:17 AM   #12
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Thanks for the help!
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Old 07-02-2003, 11:24 AM   #13
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Default 30 vs 50

I registered just so I could add my $.02. I ran 50 weight for a week and 30 weight for a week (Mobile 1) and I have a SPA oil temp/pressure gauge accurate to 1/10 degree F and LBS.

50 weight hot (85+ ambient, AC on, in traffic)
F = 195-210
LBS = 30-35 idle, 90-100 WOT

30 weight hot
F = 185-195 (never over 200 so far)
LBS = 24-30 idle, 87-95 WOT (never over 95 so far)

So it would appear in my very unscientific test that 50 weight did increase pressure and temperature in the lubrication system. John
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Old 07-02-2003, 02:42 PM   #14
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Cold hard facts! That's what I like to hear......er, um read. Thanks for the info.
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Old 07-02-2003, 03:42 PM   #15
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The problem with thicker weight oils like 15w-50 is that the don't flow as well when the engine is cold and have a tendancy to not flow well through the small openings in the engines lubrication system possibly starving some parts for oil, and also most likely reducing the life span of the oil pump.

With a liquid cooled engine therotically there will not be that much temperature varation of the coolant and oil since the engine is regulate to run at about the same operating temperature no matter what load and ambiant temperature the engine might experience.

The engine oil is cooled/heated by the engine's coolant, there is an oil to coolent exchange unit in WRX's. So oil temp will probably only fluxuate by maybe 40 degrees once it has reached normal operating temperature. I don't think thats enough temperature varation that anyone would care to use the thicker weight oils.

Cold start is what most people worry about. After the engine has been sitting a while all the oil will be pulled by gravity to the lowest point in the engine. Becasue of lack of oil in the upper engine parts, during startup is when most of the engine wear occurs. Which means you want the easist flowing oil possible, so that the pump can pump it out of the oil pan into the engines interals as quickly as possible to reduce wear. Thicker oils don't lubricate as well during start up becasue they are harder to pump. Oil thickness has little to do with is ability to adhear to a surfice, ie coating ability. Viscosity measures its flowability.
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Old 07-02-2003, 10:19 PM   #16
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One thing that I've noticed about WRX owners is that they are very particular and tend to be very well informed. Since I make my living in the performance oil industry (no, not Kragan) I'd like to contribute to your wisdom here, if I could.

A common misconception about multi-grade oils is that the 0W, 5W, 10W, 15W, and 20W are just cold temp measurement of the SAE grade oil, i.e., SAE 20, 30, 40, & 50. That simply isn't the case.

The W measurement or "winter grade" (if that helps you remember) is completely unrelated to the SAE grade. If they were dependent, then why doesn't the oil get thicker with a temperature increase? After all, it just went from a 10 to a 30 right? No, oil gets thinner with increased temp.

The W grade is done with several tests, namely the Cold Cranking Simulator and Mini-Rotary Viscometer. The temperatures in which these tests are performed are extremely cold and considerably colder than 99% of us will ever experience. Try -30F up to -20F. By the time you reach the morning temp range in which 99% of us live and start our cars in, your pour point depresents are generally waning in purpose. This means that this nebulous space between the W and SAE is of little measurable importance aside from viscosity index. Actually, most grades of oil are imperceptibly different at 50F- 80F sitting in your case.

Compared to the older smog beasts of yester-year, our new cars are so efficient in starting and pumping "cold" oil that the SAE dropped the temperatures in the W tests another 5 degrees!

Your SAE grade is where you are at 212F or 100C (for those of you north of the border). SAE grades are measured by a unit called centistokes which describes viscosity. If that raw number falls within a range of say 9.5 to 12 cSt/100C then it's a SAE 30 crankcase oil. The range for 30 is relatively small, whereas 40 is larger and 50 is larger still. That's why some cheap oils meet the SAE 30 spec while fresh, but then immediately fall out of grade. The API never said how deep you need to be "in-grade", just that you are.

You's be shocked to see how some of your favorites rank on these tests.

The pros and cons of higher SAE grades would take up another page so I'll save that for later.
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Old 10-22-2003, 01:02 PM   #17
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sorry to revive this, but I would really like a continuation of the explanation of oil, and pros and cons of heavier weight, as everyhting I read out there seems slightly contradictory or just hard to read/understand. I like what squeeze said and would like him or someone else to finish.

Thanks



(and I am not nearly obsessed enough with oil to read bobistheoil guy for long enough to extract this 'newbish' information...)

edit: also isnt a larger difference between the 'winter' grade and sae grade not as good as a smaller difference (something to do with difficulty to manufacture?) And to clarify, you said the range for 30 is small, does that mean while 50 is thicker at 100C, it has a greater range, and is this a bad thing?

Last edited by lotuseatsvipers; 10-22-2003 at 01:09 PM.
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Old 10-27-2003, 09:55 PM   #18
lotusdrift
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well the thread has enough views...

eh no help huh! bummer...
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