Amazon has
5-Quart Castrol Edge High Mileage Advanced Full Synthetic Motor Oil (0W-20) for $22.32 - 5% when you check out via Subscribe & Save =
$21.20.
Shipping is free w/ Prime or on $35+ orders.
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SUCHaDEAL for finding this deal.
About this item:
- Phosphorus Replacement Technology to help extend the life of the emission system
- Reduces leaks, oil burnoff and power robbing deposits
- 15,000 miles between oil changes*
- Meets or exceeds the following specifications: API SP/SN PLUS/SN/SM | ILSAC GF-6 | Meets engine test requirements of Chrysler MS 6395 | Meets Ford WSS-M2C947-B1 | Meets Ford WSS-M2C962-A2
- *Or one year, whichever comes first
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That all goes back to a famous lawsuit between Mobil and Castrol in the 1990s (yes, that Castrol).
Base oils are traditionally classified into five groups. Groups I, II, and III are derived from conventional crude oil. Groups IV and V are what were originally considered real synthetics — chemically engineered hydrocarbons like PAO, esters, polyglycols, or silicone. Mobil pioneered much of this technology.
For a long time, only Group IV and V oils could legally be labeled "synthetic," and they commanded a premium because they retained their physical properties far better.
In the 1990s, Castrol started using highly processed Group III base oils and marketing them as synthetic. Mobil sued, arguing that Group III was still conventional oil. Mobil lost. Castrol's argument was that Group III oils are so heavily processed that calling them synthetic was justified.
Fast forward to today: in the U.S. (but not in places like Germany or Japan), "synthetic" can legally mean Group III, IV, or V. So "100% synthetic" can be 100% Group III — which pre-1990 would not have been considered synthetic at all.
"Synthetic blend," meanwhile, can be basically any mix of Group I–II with Group III–V.
So yes — Castrol Edge High Mileage Advanced Full Synthetic made in the U.S. is, you guessed it, Group III. But Castrol Edge Full Synthetic made in Germany (even with the same name) is typically a true Group IV oil.
Given how screwed up the labeling system is, I just stick with Costco.
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That all goes back to a famous lawsuit between Mobil and Castrol in the 1990s (yes, that Castrol).
Base oils are traditionally classified into five groups. Groups I, II, and III are derived from conventional crude oil. Groups IV and V are what were originally considered real synthetics — chemically engineered hydrocarbons like PAO, esters, polyglycols, or silicone. Mobil pioneered much of this technology.
For a long time, only Group IV and V oils could legally be labeled "synthetic," and they commanded a premium because they retained their physical properties far better.
In the 1990s, Castrol started using highly processed Group III base oils and marketing them as synthetic. Mobil sued, arguing that Group III was still conventional oil. Mobil lost. Castrol's argument was that Group III oils are so heavily processed that calling them synthetic was justified.
Fast forward to today: in the U.S. (but not in places like Germany or Japan), "synthetic" can legally mean Group III, IV, or V. So "100% synthetic" can be 100% Group III — which pre-1990 would not have been considered synthetic at all.
"Synthetic blend," meanwhile, can be basically any mix of Group I–II with Group III–V.
So yes — Castrol Edge High Mileage Advanced Full Synthetic made in the U.S. is, you guessed it, Group III. But Castrol Edge Full Synthetic made in Germany (even with the same name) is typically a true Group IV oil.
Given how screwed up the labeling system is, I just stick with Costco.
That all goes back to a famous lawsuit between Mobil and Castrol in the 1990s (yes, that Castrol).
Base oils are traditionally classified into five groups. Groups I, II, and III are derived from conventional crude oil. Groups IV and V are what were originally considered real synthetics — chemically engineered hydrocarbons like PAO, esters, polyglycols, or silicone. Mobil pioneered much of this technology.
For a long time, only Group IV and V oils could legally be labeled "synthetic," and they commanded a premium because they retained their physical properties far better.
In the 1990s, Castrol started using highly processed Group III base oils and marketing them as synthetic. Mobil sued, arguing that Group III was still conventional oil. Mobil lost. Castrol's argument was that Group III oils are so heavily processed that calling them synthetic was justified.
Fast forward to today: in the U.S. (but not in places like Germany or Japan), "synthetic" can legally mean Group III, IV, or V. So "100% synthetic" can be 100% Group III — which pre-1990 would not have been considered synthetic at all.
"Synthetic blend," meanwhile, can be basically any mix of Group I–II with Group III–V.
So yes — Castrol Edge High Mileage Advanced Full Synthetic made in the U.S. is, you guessed it, Group III. But Castrol Edge Full Synthetic made in Germany (even with the same name) is typically a true Group IV oil.
Given how screwed up the labeling system is, I just stick with Costco.
https://www.mobil.com/en/lubrican...il-1-0w-20
https://a.co/d/0hbsdr85
Both Castrol EDGE High Mileage 5W-30 and Pennzoil Ultra Platinum 5W-30 are marketed as full synthetics in the US, but as you correctly pointed out (referencing the Mobil vs. Castrol lawsuit and the resulting NAD/NARB ruling in 1999), the term "synthetic" here legally encompasses Group III base stocks derived from highly hydroprocessed crude oil or equivalent processes. Neither oil qualifies as a "true synthetic" under the pre-1990s definition (i.e., primarily Group IV PAO or Group V esters/polyglycols, which are chemically synthesized from non-crude sources like ethylene). At their typical retail price point (~$25–$35 for 5 quarts), this is standard—true Group IV/V oils like Amsoil Signature Series, Red Line, or certain Mobil 1 formulations (which often blend PAO with Group III) command a premium and aren't commonly found in big-box stores without upcharges.
Here's how they stack up specifically in terms of base oil composition, performance implications, and overall ranking based on the criteria you raised (focusing on "true synthetic" purity, thermal stability, and long-term engine health). This draws from manufacturer data sheets, MSDS, independent lab analyses (e.g., from forums like Bob Is The Oil Guy), and industry testing standards like ASTM D5800 (volatility) and Sequence IIIH (oxidation stability).
### Base Oil Composition
- **Castrol EDGE High Mileage 5W-30**: Primarily Group III hydrocracked base stock from crude oil (80–85% highly refined mineral oil per MSDS). It includes some synthetic additives for high-mileage benefits (e.g., seal conditioners like elastomers to reduce leaks and oil consumption in engines over 75,000 miles). No significant Group IV PAO content in the US formulation—confirmed by viscosity index (~160–170) and pour points (-39°C) that align with advanced Group III rather than PAO's superior low-temp flow. The German/European version (often labeled as Castrol EDGE Professional) does incorporate more Group IV for stricter ACEA standards, but the US product is optimized for cost and API/ILSAC compliance. This makes it a solid "legal synthetic" but not a standout in purity or resistance to breakdown compared to pre-lawsuit benchmarks.
- **Pennzoil Ultra Platinum 5W-30**: 100% Group III+ base stock via Shell's patented PurePlus Gas-to-Liquid (GTL) process, converting natural gas (methane) into a crystal-clear synthetic base oil. MSDS lists it as "synthetic base oil and additives" with highly refined components (<3% DMSO extractables, indicating ultra-low impurities). GTL isn't classified as Group IV (which requires PAO from ethylene oligomerization), but its molecular structure is more uniform and impurity-free (99.5% pure per Pennzoil claims) than traditional crude-based Group III. This results in performance metrics closer to Group IV: lower volatility (Noack ~6–8%), better oxidation resistance, and superior cleanliness (e.g., 40% cleaner pistons in Sequence IIIH tests). It's not a "true synthetic" by strict definition, but it's a step above standard hydrocracked Group III in real-world durability.
Both will outperform conventional or blend oils in your V6, providing strong LSPI protection and up to 10,000-mile intervals via the oil life monitor. However, if you're disillusioned with the labeling (as per the lawsuit), consider stepping up to a confirmed PAO-based oil like Mobil 1 Extended Performance 5W-30 (dexos1-approved, ~50% Group IV blend) or Amsoil (pure Group IV, but pricier at $40–50/5qt). Your Costco preference aligns—Kirkland Signature Full Synthetic is typically a Group III hydrocracked oil (rebranded Warren or Mobil), similar to Castrol, and a budget-friendly dexos1 option at ~$20/5qt.
That all goes back to a famous lawsuit between Mobil and Castrol in the 1990s (yes, that Castrol).
Base oils are traditionally classified into five groups. Groups I, II, and III are derived from conventional crude oil. Groups IV and V are what were originally considered real synthetics — chemically engineered hydrocarbons like PAO, esters, polyglycols, or silicone. Mobil pioneered much of this technology.
For a long time, only Group IV and V oils could legally be labeled "synthetic," and they commanded a premium because they retained their physical properties far better.
In the 1990s, Castrol started using highly processed Group III base oils and marketing them as synthetic. Mobil sued, arguing that Group III was still conventional oil. Mobil lost. Castrol's argument was that Group III oils are so heavily processed that calling them synthetic was justified.
Fast forward to today: in the U.S. (but not in places like Germany or Japan), "synthetic" can legally mean Group III, IV, or V. So "100% synthetic" can be 100% Group III — which pre-1990 would not have been considered synthetic at all.
"Synthetic blend," meanwhile, can be basically any mix of Group I–II with Group III–V.
So yes — Castrol Edge High Mileage Advanced Full Synthetic made in the U.S. is, you guessed it, Group III. But Castrol Edge Full Synthetic made in Germany (even with the same name) is typically a true Group IV oil.
Given how screwed up the labeling system is, I just stick with Costco.
Review on costco says their's are group 3 too.
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FYI Castrol Edge 5w 30 is $70 FOR ONE LITER in Germany! You DO NOT want to go there on this hot button topic, Europe is killing car enthusiasts with their stupid green and carbon laws, taxes, et...
Labelling conventions or not, you can get superior, top-level oil here in the U. S. for FAR less. Just do some basic research. This Castrol oil is fine for many people, but it isn't a top tier synthetic.
Try not to get caught up in the "my-base-oil-versus-your-base-oil" cage match. The base oils that go into the oil aren't as important to your engine as the performance that comes out of the oil. Look for motor oils that offer performance claims backed by industry-standard testing or real-world results. That's what's really important.
Generally speaking, Group IV base oils offer the best performance, Group III second best, and so on in reverse order. But be forewarned – there are exceptions. And, you can't judge motor oil performance solely on base oil type.
Some motor oils made from Group III oils can outperform some Group IV motor oils. That's because the final formulation is a function of the base oils and additives working in tandem. Like base oils, additives come in a range of qualities. So you could have a Group III oil with top-shelf anti-wear, anti-oxidant and other additives that outperforms a Group IV motor oil, even though Group IV base oils provide more pronounced benefits than Group III base oils. The point is, a motor oil can't be judged solely by its base oils – you need to take the entire formulation into account.
Yours truly. AMSOIL https://blog.amsoil.com/are-all-s...s-iv-vs-v/
The original thread the op posted shows "high mileage".
Don't you think this is a marketing ploy since fleet vehicle owners don't pay for that advertising nonsense to make you feel all nice?
They buy it by the barrel.
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