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Old 04-26-2001, 12:16 PM   #1
Scooby Newbie
Member#: 1865
Join Date: Jul 2000
Location: Columbus, Ohio, USA
Post Oil switching/mixing question

Okay, here's the deal. I'm an idiot apparently, and forgot to remove the o-ring from the drain plug when I changed the oil on the RS back in October. Anyways, a few weeks ago it started to leak down at the seal, so I took it in (unaware that I had forgoteen to remove the first o-ring) and dropped it off at the dealer. When I picked it up that night, they told me what the problem was and that they had gone ahead and done an oil change since they had drained the oil taking off the plug to find out that I had two o-rings on. They didn't, however, replace the filter.

So here's my question - when I changed the oil I switched over from whatever dino oil Subaru uses to Mobil 1 10W-30 synthetic. When they "changed" my oil when I took it in, they presumably replaced by Mobil 1 w/ regular dino oil. Since they didn't replace the filter, there was surely a good amount of the Mobil 1 in the filter. Now, the Mobil 1 has mixed with the dino oil. Is this mixing bad? Can it cause problems? Just wondering. TIA!
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Old 04-26-2001, 12:23 PM   #2
Scooby Newbie
Member#: 1367
Join Date: Apr 2000
Chapter/Region: MWSOC
Location: Cleveland, OH, USA
2000 Impreza 2.5RS
Blue Ridge Pearl


Mixing synth oil with dino oil is not recommended by any oil producer that I can think of. Your safest bet if to just go ahead and change the oil and the filter again.
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Old 04-26-2001, 12:32 PM   #3
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Chapter/Region: Tri-State
Location: N.J.
04 FXT


IMO, it wouldn't be a problem. A lot of companies offer a synthetic/dino blend anyway. Mobil is one of them. Since it probably had 5W30 before, I guess you have a 9.5W30 now. I wouldn't worry especially if you change it within 3-6000 miles.


[This message has been edited by bluesubie (edited April 26, 2001).]
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Old 04-26-2001, 12:34 PM   #4
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Member#: 3584
Join Date: Jan 2001
Location: USA

I don't see any reason why dino and synthetics cannot be mixed. Any urls from a reputable place that says this? Any time you switch from dino to synth, there will be a bit of a mixing as you cannot completely drain the oil out entirely.

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Old 04-26-2001, 12:34 PM   #5
Scooby Specialist
Member#: 2817
Join Date: Nov 2000
Location: NYC and Troy, NY
2001 Impreza 2.5RS


I had synthetic in the engine, but added 1/2 quart of regular oil by accident. No problems.

But, it is not recommended to mix 2 different oil.
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Old 04-26-2001, 02:59 PM   #6
mike moniot
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Member#: 5999
Join Date: Apr 2001
Location: San Miguel de Allende, Gto.
'02 wrx spt wagon


I would agree, but I don't think I would use extra virgin olive oil in an emergency - otherwise anything is fine. I use Castrol 5-50 Synth in my '90 325 is and Valvoline 20-50 Synth in my M 6 here in Dallas. I plan to use Mobil One 15-50 in the '02 REX 5sp wagon (I'm a XOM shareholder). Any thoughts? M
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Old 04-26-2001, 03:07 PM   #7
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Join Date: Dec 2000
Location: Portland, OR USA
2005 GT LTD Wagon
Garnet Red


OK, here's the deal. Mixing types of oil, even between manufacturers isn't going to do any harm, but it's likely going to shorten the life of the oil.

Depending on the quality of the petroleum base that is used, and the desired properties of the oil, a different set of additives will be used to either stabilize the base, or change the operating characteristics of oil. So, the set of additives in one brand/type of oil, may defeat the additives in another.

So, if you mix oil - synth and dino, or even the same type, but different manufacturers, don't count on whatever 'special' properties one brand markets. Assume it's just plain old generic oil and change it at 3k, like a good boy.
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Old 04-26-2001, 03:18 PM   #8
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2002 WRX Sedan
2006 Outback 3.0R


Every synthetic I know of is fully compatible with dyno oils. Don't worry about it.
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Old 04-27-2001, 01:02 AM   #9
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Member#: 1865
Join Date: Jul 2000
Location: Columbus, Ohio, USA

Thanks, guys. I'm actually going to do an oil and filter change tonight.

FWIW - I've noticed some rougher taking off out of 1st gear since the "change" by the dealer . . . to the point of almost stalling out. I'd like to think it wasn't my driving that was causing this.
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Old 04-27-2001, 01:07 AM   #10
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Join Date: Sep 1999
Chapter/Region: Tri-State
Location: Long Island, NY USA
2004 Impreza WRX
Java Black Pearl


Synthetic blend oil = Regular plus pure synthetic.

So it shouldn't be a problem. The only concern should be mixing oils of different service ratings. IIRC the newest is "SJ". You'll find it on the back of the container.
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Old 04-27-2001, 01:23 AM   #11
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Member#: 2060
Join Date: Aug 2000
Chapter/Region: BAIC
Location: Bay Area
00 2.5RS Coupe
01 black boxster hardtop


Where do you guys get this infomation? Mixing synthetic and regular oil is not a problem. I would like to see anything you can find that says otherwise. As for any strange running/stalling of the engine, its most likely the ECU/knock sensor problem of when the oil is first pumped through a new oil filter. Do a ECU reset and you should be good.

Chris Brunell

[This message has been edited by A4Killer (edited April 26, 2001).]
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