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2021 Outback Limited 2.5L - 馃崷The Ice Cream Man馃崷
5,506 Posts
Discussion Starter #1
Well after spending way too much time looking through the seemingly endless (and sometimes brainless) discussions over over the past couple days and I thought I'd start up some talk here other than in the Favorite Oil poll.

Anyway for me I've always been a fan of Castrol petroleum oils although not of Castrol Syntec. I have used Castrol Semi-Syn although I've actually read reports that the standard Castrol GTX outperforms Semi-Syn as well as Syntec is most categories. That being said there are also many reports that show that Castrol GTX High Mileage outperforms the standard GTX. Blah Blah Blah... anyway I'll stick to my dino guns with Castrols petro oils.

As far as synthetic's go, I've been pretty conflicted as of late. The two leading synthetic oil producers are Mobil 1 and AMSOIL, here's my take on the two:

1. Mobil 1 is a TRUE full synthetic, one of the cheapest and most readily available oils on the market today. Comes as a factory fill in many higher end cars, endorsed and commended by many.

2. AMSOIL is one of the first synthetic oils, IT IS NOT a True full synthetic (as many tests show) although it outpeforms Mobil 1 and every other oil in about every category. More expensive than most oils (including Mobil 1) and somewhat hard to find. AMSOIL users typically stand religiously behind the product, other AMSOIL products (filters, other lubes) are of the highest quality available.

Chat on about whatever oil related stuff you want, feel free to reference or bring in any info form Bob's site as well :D

Superb Moderator, ,
6,185 Posts
I use Mobil 1 in my engine. I like it. It is readily available and if you get it at Wal Mart it doesn't break the bank. Regarding Amsoil, I researched it and due to the availability and price, I went with Mobil 1. Now, I've said it before, and I'll say it again-my opinion ---If Amsoil is so great, how come not one car comes with it from the factory? Mobil 1 has a couple to say the least. I, like Kevin, am going to try the Mobil 1 in my rear diff sometime soon, so I can give you another objective. But as for engine oil, Mobil 1 has treated me fine so I don't foresee a switch in the future. Brian

MY99 3rd Gen Outback GX, 2004 Lexus RX330 Sport Luxury
241 Posts
Well, as discussed over at BITOG too, "most" Castrol oils are NOT synthetic, even though they may be marketed as such. Some of the Syntec/Formula/Formula R Synthetic (branding depending on market) are Group 3 Hyrdocracked oils (ie, semi synthetic). The exception are a few European and Asian Castrol oils like the infamous "German Castrol" SLX 0w30, 10w60 and 0w40.

Both my Outback and Mazda specifiy a 5w30 oil in the owners manual. However, a 5w30 full synthetic is basically non-existent here in Australia, with the exception of Redline. I'm very anal about caring for my cars, but even Redline's prices in this country are a little hard to swallow. :(

I have chosen Motul 8100 0w40 for the Outback, and Mobil 1 0w40 for the Mazda. Both are full synthetic - PAO group 4 (M1) and Group 4 / 5 Ester (Motul). Most at BITOG claim that 0w40s aren't shear stable, but "so what", if it shears down it'll still be a 30w, which is what the manufacturer recommends anyway.

Mobil 1 10w30 is available in Oz, but with a CST of 10, it's a little too "thin" for my liking in this temperature and climate.

194 Posts
Well, I use Amsoil in all my vehicles. The higher cost is normally offset by the longer drain intervals. Plus in this day and age, getting the oil is almost as easy as reading the forums.

BTW, just got a shipment in today. Fresh gear oil, fresh motor oil and some filters. Founder
2021 Outback Limited 2.5L - 馃崷The Ice Cream Man馃崷
5,506 Posts
Discussion Starter #5
Uhg! I just spent 2 hours of my early morning last night drudging through some more threads at BITOG. That place is like a black hole, it just sucks you in and you can't get away! :eek: Well after doing multiple searches on different topics and doing excessive research here are the conclusions I've come to:


95% of people switching to synthetic meet their needs with Mobil 1

The other 5% will use AMSOIL, Redline, Royal Purple, etc due to their specific requirements


Probably the best petro oil is Schaffer's, although because its pretty **** hard to get ahold of my vote goes to Castrol GTX or Castrol GTX High Mileage

When talking about synthetics Mobil 1 is the best value for your money. Many other more premium (priced) oils are certainly better for certain types of drivers or situations. I'll list some examples below:

AMSOIL: The only real benefit I can see with this oil over Mobil 1 is their great oil change intervals. This is ideal for persons who do a lot of highway driving or take long distance trips on a regular basis. A good example would be Mericet

Redline: Probably the best high performance oil you can buy, period. The heat capacity for this oil is simply incredible, along with having the largest and possibly best additive package of any oil available it definately sets the standard for all racing oils. To get all this you have to pay a serious premium, the lowest I've seen it was $7/quart although most places usually sell it for $8-10+/quart

Lord of ScoobyMods, ,
19' Impreza Sport 5 dr / 01' Forester S / 13' OB CVT / 10' Legacy 3.6R / 99 Mita MX-5
1,213 Posts
Here is a post that was on a list I belonged to a while back. I always take stuff I read on the net w/ a grain of salt but I thought it was informative:


Dear Peter and list subscribers,

I am a chemist who used to work for one of the large chemical companies who supplied the basestocks for synthetic lubricants; one of my customers was Redline; I helped them design the basestock combinations for a number of synthetic applications. Based my my extensive experience with synthetics, I would recommend at least 5,000 mis prior to changeover to synthetic. You WANT wear in the first few thousand miles so that the metal is completely smooth. The lubrication qualities of synthetic will keep the molecular "peaks and valleys" that result from even the best of machined surfaces. Use of a synthetic before this microscopic wear happens will result in incomplete seating of rings, bearings,etc. which will decrease long-term efficiency and performance.

After a 5-10K breaking with ideally "cheap" oil, you then "stop" wear with the better lubricity of the synthetic. I stick with the factory drain intervals at 5K, even at first oil change, although the basestocks for synthetic hold up for much longer, the additives do become depleted.

The small amount of mineral present after change will entirely mix, and be surrounded by synthetic basestock so there is a minimal need to "flush" the crankcase. The darker color is due to the affinity for the synthetic to solubilize varnish and sludge deposits throughout the engine. Synthetic can support about 10x the dirt, varnish, etc. compared to mineral oil without damage to engine. Oil filters do tend to get loaded up faster w/synthetic.

Regarding the use of synthetic in the manual tranny, the pour point of the PAO basestocks used in redline, Amsoil, and Mobil 1 is approximately minus 80F; certainly low enough to improve lubricity at temps encountered in US and most of Canada. The EP additive makes sense to enhance extreme pressure antiwear performance in a manual trans, since there are many points where the oil is being "squeezed" metal to metal in the transmission; the EP additives provide a sacrificial microscopic film of phosphate-sulphur additive to keep the metal from contacting, even when the oil is completely squeezed out of the space. Since it is sacrificial, you should change out oil with new additive every 40K miles, just to make sure. I don't believe that you will find that the EP additive will contribute to improved shifting while cold,
it will only reduce gear wear over the long run.


MY99 3rd Gen Outback GX, 2004 Lexus RX330 Sport Luxury
241 Posts
Interesting reading Peaty. :)
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