Castrol Syntec 10W-40

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Dec 18, 2002
You have one chance to convince me NOT to put Castrol Syntec 10W-40 in my engine. I have a 1998 Subaru Impreza 2.5RS with almost 80k miles. The manual allows for a range of viscosities. I would like to use 10W-40 this summer. I would also prefer the oil to have ACEA A3 rating. Out of the oil available to me locally I can only find Castrol Syntec, Castrol Synthetic Blend and Valvoline Durablend to fit these requirements. I looked at Castrol Synthetic Blend and it seems to be a little too thick for my liking. Syntec, on the other hand, is on the thin side of 40 weight, which is what I prefer. The car has been run on Mobil 1 5W-30 since new. I almost decided to try Castrol Syntec 10W-40. I knw it's Group III. But it's cheaper than Mobil 1, so the price seems to reflect the cheaper base stock. Well, actually with the 5 quart canisters at my local WalMart Mobil 1 is slightly cheaper. But it is not available in 10W-40. 15W-50 is way too thick to my liking and 10W-30 does not have ACEA A3 rating. Maybe I should just use Mobil 1 10W-30? Or maybe I should use a quality non-synthetic, such as Motorcraft 10W-40. I use it in my other Impreza and it seems to like it a lot. What do you say? Syntec, Mobil 1 or just a quality non-synthetic? I don't mind changing it at 3k miles. For winter I plan to use Castrol SLX 0W-30.
If it were mine, I'd stick with the Mobil 1, or maybe switch to the German Syntec 0w30. As far as "protection," I can see absolutely no advantage to using Syntec 10w40 over either of these two oils for summer driving.
I agree, go with the Syntec 0w30 since it's probably roughly the same price, but is definitely a full synthetic (the German version that is) And the 0w30 is almost a 0w40 anyways, and that Syntec 10w40 would turn into 10w30 pretty rapidly most likely. So after 2000 miles in your engine the 0w30 would end up having a thicker viscosity at 100c. If you were planning on using this oil in the winter, you might as well use it in the summer too.
Go for it. Better yet, give us a UOA when you're finished with it. You may even prefer it over the M-1 have. Certainly won't miss the consumption (if you have any)...
Originally posted by Dr. T: Go for it. Better yet, give us a UOA when you're finished with it. You may even prefer it over the M-1 have. Certainly won't miss the consumption (if you have any)...
That's exactly the thing. I do, and it seems to have something to do with PCV system. Some day I will fix it but at this point I just want to get rid of consumption. I want to try something a little thicker, especially since the owner's manual allows for as much as 20W-50. I am struggling between using Motorcraft 10W-40 for 3 months or Syntec 10W-40 for maybe a little longer, maybe not. I usually go 6 month between changes with Mobil 1 and plan to do the same with Castrol SLX when I put it in for the winter. I am convinced at this point that Mobil 1 5W-30 will eventually cause consumption if used for a long time. Not so sure about 10W-30. 5W-30 seems to thin out a lot and that is what causes consumption, eventually. Mobil 1 10W-30 seems to be much better in this regard. It is tempting to put Castrol SLX in it now but I only have 6 liters of it and who knows when I will be able to buy more, since local AutoZone store does not carry it yet. They have about 20 bottles of old non-SLX 0W-30 on the shelf and I am guessing that will last a very long time there [Frown] And who know when I will be in Toronto next time, with SARS and all... [I dont know] So I have to save my SLX for the winter...
I would use Mobil 1 10w-30. It may not be the absolute best, but UOA's as a rule have been very good. And it is available everywhere.
For Pete's sake quit worrying about SARS. Sheesh. Use the 0w-30 now. And take a nice drive in the beautiful Fall colors across the frontier and get some more for the Winter.
Go for it and please post a UOA. It is one of the very few ACEA A3 synthetics that I can find OTC. BMW North America discontinued the 5W-40 Syntec, so the 10W-40 may be a good replacement. I know that the 0W-30 has a lot of fans here, but the German stuff is not stocked everywhere and is too thin for some applications.
1) As far as grade, anything from 0W-30 to 20W-50 has good UOA's in Subaru engines. 2) If you want peak performance at all times and long engine life, stick with synthetic. If you want economically priced oil, go with a mineral oil. If you want a combination of the two, get a blend. 3) I am certain the syntec will work fine at least for regular drain intervals. But since Mobil 1 is cheaper that Syntec where I live, Syntec would be the big loser in my pick. 4) Do at least 1 or 2 oil analyses with whatever you chose to see how the oil works in your car, and how long is reasonable to run it. 5) Bottom line; Mobil 1 10W-30, 15W-50, or a mix of the two would be my choice. My opinion is based on this:
Well, according to Kelley Blue Book, you're car has a trade-in value of about $7300, assuming it's in excellent condition. Thus, I'd suggest just going for something simple like Chevron Supreme 10W-30 (which this board tends to approve in the 'dino' category) at 3000 mile change intervals, skipping the UOA and enjoying all of the time and money you'll save.
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