Mobil 1 0w-40 vs German Castrol GC 0w-30

[brian]

I am comparing these two oils and cannot find a thread that already summarizes the differences. From what I have read they are comparable. In my experience GC 0w-30 is shear stable. It makes it 10,000 miles in my Jeep 4.0 and stays in grade. I have read that Mobil 1 0w-40 shears down until it is slightly thicker than the GC 0w-30. Do both turn in comparable UOA's? Has anyone tried them back to back in the same engine to compare? Regards,

 

[buickmaster]

i went thru the same dilemma recently and one major diff is that m1 has moly and gc doesn't. not sure the significance. i chose the gc 0w30 just to try something new. i had m1 0w40 in another car before. everyone told me that either will be good.

 

[Audi Junkie]

I use GC. If you need 10k oil changes, yeah...synth. Either oil is great for extended changes, but I actually prefer more changes of dino oil. Say 5k on dino vs 10k on ANY synth, I think dino gives a better result for the same money. You might want to look at Pennzoil Platinum too, unless you need the thicker visc of the two you mentioned. Bottom line is try them yourself, and compare and consider plain yellow bottle Pennzoil...there is no shame in that.

 

[wapacz]

Choose which ever one you can find the cheapest . They are both good oils.

 

[Gary Allan]

 Quote:

In my experience GC 0w-30 is shear stable.

appears to be

 Quote:

I have read that Mobil 1 0w-40 shears down

appears to. I don't know why they make it. It has to be a marketing designation to distinguish itself from other 0w-30 M1 products.

 

[brian]

Gary, One difference is that Mobil 1 0w-40 is formulated in order to meet the A4/B4 specs which mandate a higher HT/HS. GC 0w-30 also meets the A4/B4 specs. Brian

 

[Audi Junkie]

"A4"?

 

[Gary Allan]

 Originally Posted By: brian

Gary, One difference is that Mobil 1 0w-40 is formulated in order to meet the A4/B4 specs which mandate a higher HT/HS. GC 0w-30 also meets the A4/B4 specs. Brian

Yes. So ... No one seems to be bothered by the fact that it's marketed as a 0w-40 ..yet never remains a 40 weight for more than 5 minutes in anything that spec's it. So it's a 0w-30 that meets all those spec's ..but is tweaked to allow it to wear a 0w-40 label ...100% for marketing purposes. Do I have it wrong? It's the greatest 0w-40 that barely was I keep thinking that I dialed that wrong portal address and landed in that slightly different parallel universe again. It's sooooooooo close to right.

 

[Doug Hillary]

Hi, Gary - Referring to M1 0W-40 you said: "I don't know why they make it. It has to be a marketing designation to distinguish itself from other 0w-30 M1 products. M1 0W-40 is not in the same formulation realm as "other 0W-30 M1 products". Many Euro engine makers have extended viscosity test protocols usually based on ACEA's A3/B3. In the case of Porsche their requirement is that the lubricant remain in the SAE30 realm after these extended tests. That is why no SAE30 lubricants are Approved - Castrol Formula SLX 0W-30 (GC) was up until 1999 That is why they make it - and that is just one reason why it is in so many expensive engines as a Factory fill

 

[pickled]

Hi Doug, Now I am curious. If a XW30 did not sheer down, and met the other stated requirements of the OEM could we assume that it would be a decent performer over the prescribed OCI even though it didn't bear the "approval" or was a "factory" filled oil. Just trying to see if I can help some folks save some grief here.

 

[Audi Junkie]

GC makes a +150c HT/HS of 3.5cP with a 12cSt (+100c) base. Mobil 1 0w-40 needs a 14cSt oil to make the same HT/HS. GC = better and a more exotic base.

 

[Gary Allan]

 Quote:

That is why no SAE30 lubricants are Approved - Castrol Formula SLX 0W-30 (GC) was up until 1999 That is why they make it - and that is just one reason why it is in so many expensive engines as a Factory fill

Okay ..so they overshoot their target "final visc" so that they can jump through those hoops ..even though it fails to remain in a 40 grade in every engine I've seen UOA on. So they don't bother just tweaking it up a Cst or half to allow it to be a 40 grade when you turn the key for the 10th time? Why am I the only one that sees this as a the last thing I'd boast about? It appears to be a well managed failure (if for nothing more than getting the 0w-40 label). We aim just a little high because we really can't go the distance! Now that would be a real marketing slogan to capture the essence the unique advantages of this fluid Now ...hmmm...I'm surely perseverating on this here ...but (again) I find it most odd that the most raved about 0w-40 never ends up a 40 weight. No one seems to pay that any mind. Any other oil it would be a serious flaw...but not M1 0w-40. It's up there with Helix Ultra Xw-60.

 

[buster]

 Quote:

GC = better and a more exotic base

Nah, M1 0w-40 is better. This oil is designed to shear to some extent and hover the 12-14 cSt range over the course of longer drain intervals, which it does. Many oils are shear stable, but will thicken due to poor oxidation resistance. M1 is very stable. The oil has to be excellent based on the specs it meets IMO, for a 0w-40. I don't know of another oil that meets/exceeds so many engine specifications. Their are certainly weaknesses and they are the VII's and large spread. But, from what I have been reading they want to use these for other reasons. They could have easily used thicker base oils and made the oil more shear stable, but for better fuel efficiency among other things, they allow it to shear down a bit. *Notice Amsoil AFL went from 4.2 to 3.7 for HT/HS to meed the MB spec. It may not be the best in "your world", but for what is being called for right now it satisfies the OEM engine builders. This oil also has very low volatility compared to others and it will clean soft deposits. Probably from the esters in the oil. I do follow the money trail and put some amount of value on who is using this product as factory fill. I do believe that says a lot. My .02

 

[brian]

Gary, I wasn't looking towards the 0w-40 because it was touted as a 40 weight. I was looking at it because it met the A4/B4 specs. Generally anything A4/B4 will stay on the higher side of a 30 weight oil and at least be rated 30 weight or 40 weight. I was considering returning the Mobil 1 0w-40 oil that I purchased and using Mobil Delvac 1 5w-40. But now I am more curious than ever to run GC 0w-30 and the M1 0w-40 back-to-back and compare in 10,000 mile drains.

 

[Gary Allan]

Oh ..don't get me wrong. I surely don't doubt Doug, buster ..or anyone else. I'm not "attacking" the oil for its lack of merit. I'm just stuck on this inevitable shearing that is very counterintuitive to me as being "right". When something is "unright" ..regardless of the environment/topic/whatever, I need to have it rationalized/reasoned. So far I haven't gotten an authoritative "why" you make an oil that shears by design. I've heard that it does and that it meets all kinds of great spec's and is OEM for many fine exotic engines ..and that's about it. ..but take a look at Dr. Haas's factory fill of Helix Ultra (Ultra Helix?) 10w-60. His UOA showed that it sheared to a 30 grade, iirc. It's kinda like refried beans ..why not just fry them proper the first time around So, for me, this spells a new limbo/mombo. Oils with preferred and managed and designed decay features. I'll adopt a new term if one is offered. Again, ..no one seems to pay it any mind. That's probably the real thing that causes me to

 

[Eddie]

I vote for the Mobil 1 0w40. If you do try to compare UOAs, run two fills in sucession on each oil and use the second run for the UOA. For some reason the first UOA is not representative, possibly due to not being able to drain 100% of previous fill. JMO Ed

 

[Volvohead]

I've run 'em both. No UOAs, but both are very good performers with good base oils. The M1 starts at a 40 but is quick to shear down (sometimes way down) into the 30s. I can't say I agree with Buster that it's a good oil design, as some engines like a stable 40 and that's its advertised vis. IIRC, one of the high priests here once opined that it meets test sequences by oxidizing back out to a 40 by the end of the test interval. Very creative. In a high stress environment, it is not necessarily a long interval oil unless you've got sufficient sump capacity. One UOA from a fellow R owner several years ago showed it pretty much used up by 4k. GC starts at a near 40 and seems to hold its vis, however, with some thickening under heavier thermal stresses (tracking). If you offered me a case of either, I'd take the GC. But I wouldn't be upset with the M1. Delvac 1 is still one of my favorites, and I'd take it over the 0W-40, too. At this level, you are talking nuances among caviar. None of them will hurt an engine under sane usage.

 

[buster]

I understand where you are coming from Gary. I tend to be on the fence with this oil, but the endorsements have swayed me to believe that it's a decent oil. However, it could just be an oil that is average, and not great. A global formulation that is "adequate", rather than stellar, for the OEM cars it's filled in. XOM does have shareholders to answer too and they could potentially cut corners. It's complicated. Hard to really know.

 

[JAG]

 Originally Posted By: Gary Allan

Again, ..no one seems to pay it any mind. That's probably the real thing that causes me to

I pay it a lot of mind. Those polymers add viscoelastic properties to the oil which can benefit bearings even when sheared. Those polymers also tick me off for other reasons like: - Decreasing oxidative/thermal stability - Increasing propensity toward deposits - Possibly decreasing ring seal due to deposits on rings and piston grooves. This gives rise to all sorts of negatives like increased fuel dilution, more flow of nasties through the PCV system, increased oxidation and nitration, etc. I think I could tell the formulators how to make a variation of this oil that would be better in some ways but it would get maybe no longer be a 0W oil and it may not pass the fuel economy requirements of MB 229.5. It probably would pass it for MB 229.3 though, as some 5W-40 oils do. BTW, I've had bad experiences with Gold GC in both my vehicles. I think it gets its high viscosity index from a high viscosity index FLUID rather than a high load or polymeric VIIs. That gives the high shear stability but my testing did show that it is more volatile than M1 0W-40, which is interesting to ponder why. Clearly there is a relatively volatile fluid in GC but the details beyond that are what's interesting. M1 0W-40 has more virgin TBN than GC, FWIW.

 

[buster]

Good summary JAG.