Syntec SJ rated old bottle

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Apr 23, 2003
Ok guys. Quick question. Was Castrol Syntec ever a "True" Synthetic oil? Reason I ask is, at a walmart store, they have about 12 bottles of the older syntec 10w30 I believe. It is the older square bottles and the ratings on it were SJ. If they use to make a true synthetic is would this be it? if it is would you buy it?

One more quest. I like to run thicker oils within reason. Meaning, I wouldn't run a Dino 20w50, but I would run a Synthetic 15w50. Because the flow rate on that Mobil 1 15w50 is as good as most 5w30 Dino oils.

I know my truck calls for 5 or 10 w30 but I would assume they didn't have synthetic on their mind. I do not burn or lose any oil that I notice. But Ido have 113,000 miles on my truck. I have read some people mix like a 15w50 with 5w30. What would I have to mix for a 4 qt system to make a Mobil 1 10w40. That's about where I would like to be somewhere in that range. Thanks guys.
That Castrol Syntec SJ rated oil has been sitting on the shelf for a long time. The SL rated oils have been out for a long time. Can you find some SL-rated Castrol in the viscosity that you want?

Castrol used to use PAO in its Syntec oil. Castrol got the PAO from Mobil. But then Castrol stopped using PAO in its Syntec (in the United States) and changed the formulation. Mobil sued Castrol saying that Castrol could not call Syntec synthetic oil unless it had PAO. Castrol won the lawsuit and was given the right by a judge to call Syntec a synthetic oil.
Forget about the Castrol-even if its a true synthetic (which is daubtful-bc I think Patman's right)-it won't be as good as any SL oil.

Mixing 15W-50 and 10W-30 is a great idea (IMHO). I would go with a 25% of the 15W stuff. a 50%/50% will most certainly put you in the 40 wt. range. But I would just start with the 25% or so mixture. That puts you on the high side of 30 wt.-That's what I do.
Hey, I had the same question...and I'm not sure. I recently put in SJ 5-50 Syntec in my car because all the 4L jugs that I've seen are SJ after switching out a batch of SL Syntec I didn't want to buy 8 individual bottles.

I did find square bottles of Syntec recently. I will check, but I thought they were SH!!

Now I will re-check because I had the same question and was going to buy the old PAO stuff. But, to me it's now either too old and/or I don't really think it's better than 'newer' SL stuff.

And no, M-1 15-50 doesn't have a "flow rate" like 5-30's...the stuff is thick through and through...even at cold temps. The pour point is as low as 5-30's, but this is completetly misleading as the viscosity grade is more important than pour point and this is a 15 grade after all. However, the pumpability limit is lower because of the low pour point...and this means there is a safety margin over other, say conventinal 15 weight oils...
Meant to add that according the Syntec specs that I have for the "Old SJ" (supposed PAO), it shows that it's thicker than the current 5-50 at both 40 and 100C, which IMHO is not requied as the current HTHS is still a decent 4.5 compared to 4.8 of because of this the newer SL may provide more performance...?
I saw several (very dusty) square bottles of 0w-30 SJ Syntec this evening in a K Mart. It was A1, GF-2 rated.
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