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Old 10-17-2001, 12:01 PM   #1
db97
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Question 5w30 or 10w30???

hey, i've read several posts in which both grades were used...so which is it???

i recently switched to mobil 1 synthetic 5w30. i asked the dealer guy what i should use, and he said 5w30...however, some of you here are using 10w30...what's the difference? weight of the oil right??? doesn't the choice depend on variables such as temperature, driving style, etc.?

ever since i switched to mobil 1, my car has been running smoother (albeit louder...for some reason, the engine sounds more raucous...must be the k&n panel filter???).

anyone got any words of wisdom?

thx,
db97
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Old 10-17-2001, 03:02 PM   #2
Jon Bogert
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If you live where it gets below freezing (Louisville) you shouldn't use 10wXX in the Winter unless you park in a heated garage all the time. Use 5wXX or 0wXX.
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Old 10-17-2001, 03:03 PM   #3
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The K&N panel filter will make your engine louder, so it probably wasn't the oil. 5w for very cold ambient temperatures, 10w for normal temps.

Ross N.
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Old 10-17-2001, 07:11 PM   #4
jk147
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5w30 if you live some where that is cold, 10w30 for warmer weather.
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Old 10-18-2001, 11:14 AM   #5
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Normal driving (not auto-x or track) in cooler climes use 5W from late fall to early spring. All other times use 10W. For competition, use 15W. Works for me. South of Mason-Dixon, you're probably good with 10W ayear-round.
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Old 10-19-2001, 12:05 PM   #6
jaycee
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Is anyone using 5W50 synthetic oil (like Castrol Syntec and maybe some other brand). I figured this grade would be an all-season oil since the 5 is for winter and the 50 will be good for the hot summer. Thanks for your inputs
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Old 10-19-2001, 01:59 PM   #7
vvk
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Thumbs down

I tried Castrol Syntec last winter. Noticed a lot of valvetrain noise on cold mornings . I don't think 5W-50 should be used in our cars . Look at the specs and you can see that it's really 25W-50. Way too thick!

I use Mobil 1 5W-30 year around in the 2.5RS.


Quote:
Originally posted by jaycee
Is anyone using 5W50 synthetic oil (like Castrol Syntec and maybe some other brand). I figured this grade would be an all-season oil since the 5 is for winter and the 50 will be good for the hot summer. Thanks for your inputs
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Old 10-19-2001, 02:22 PM   #8
Richard L.
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Stay away from oils that have a wide span of viscosity, like 5W-50 or 10W-40. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. Just stick to what your owners manual recommends, like 5W-30 or 10W-30.

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Old 10-20-2001, 11:38 AM   #9
Jon Bogert
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Quote:
The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content.
Well, sure. At their limits. Which your Subaru never gets close to.
Quote:
Just stick to what your owners manual recommends
I can't even begine to imagine why anyone would follow the owners manual for motor oil. For example, the owners manual recommends 5w30 or 10w30 NON-SYNTHETIC!!! Give me a break. ANY synthetic will flow better than a 5w30 when cold and protect better than a 10w30 when hot. So much for the owners manual.

If I only took long drives or drove on the track more than once a month, I would use Redline or Mobil1 10w40 or even 20w50. In my world of frequent <30min drives, outdoor parking and cold starts, I use Mobil 1 0w40 in cooler weather. I change it often--long before the over-hyped "polymer breakdown" occurs. And my oil temps never see the far side of 230, even with the turbo on the racetrack. Do yours get higher than that? If you live in the Northern half of the U.S., the additional wear on cold start will do MUCH more damage to your engine than anything that happens once it's warmed up.

Last edited by Jon Bogert; 10-20-2001 at 11:45 AM.
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Old 10-20-2001, 11:51 AM   #10
Richard L.
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Hey Jon Bogert, give me a page in MY00 Impreza 2.5RS owner's manual that says not to use synthetic oil. Are you saying that the owner's manual is useless and people shouldn't bother reading it?

--
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Old 10-20-2001, 01:22 PM   #11
Jon [in CT]
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Neither the Owner's Manual nor the Service Manual ever mentions synthetic or non-synthetic when recommending what engine oil to use. The manuals' engine oil recommendations are based strictly on grade and viscosity.
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Old 10-20-2001, 01:45 PM   #12
Jon Bogert
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Right. That was what I meant. The manual recommends those grades of ANY oil, despite the fact that synthetic oil in many other grades exceeds in EVERY way the performance of conventional oil in the recommended grades.

So the recommendation isn't particularly adequate. So please ignore it.

Also, in general, manufacturer recommendations are for the "lowest common denominator" driver. In general, it's more useful to look at the manufacturers recommendations for the German market. In Germany the driving conditions and TUV requirements make recommending Xw30 "fuel-economy oil" not so common as in the U.S.
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Old 10-22-2001, 10:09 AM   #13
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Lightbulb

Jon B.,

Actually, the owner's manual *does* recommend the heavier weight oils. Right under the chart for the "preferred" 5W and 10W oils, it lists the heavier weight oils for severe driving.

Dennis
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Old 10-23-2001, 12:45 PM   #14
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This document helps shed some light on the situation.

Quote:

Well, sure. At their limits. Which your Subaru never gets close to.
Speak for yourself. I just put nearly three hours of track time on my Impreza last weekend.

- Steve
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Old 10-23-2001, 03:30 PM   #15
Jon Bogert
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Yeah, I was a Pocono last Friday. Even with the turbo, the oil temp was steady at 210. Pressure was fine, even on the straight. If it was warm out, I would have put in some 20W50 just to be safe.
Quote:
Speak for yourself.
I was speaking for the average driver, who shouldn't have to worry too much driving 70 on the freeway.
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