EP is said to have 50% more additives and should have a higher TBN.
EP is for extended OCI's. Regular Mobil 1 is not.
One is targeted for regular users and the other is for people who want to run long OCI's.
The standard 5w-30 meets some specific manufacturers requirements, like Honda HTO-06. It does seem odd to have so many versions, but if someone is going by the book, they have it covered and make a sale. They are good marketers as I am considering the advanced fuel economy 0-30 even though it realy isn't necessary.
We have used "regular" M1 for extended OCIs, backed with UOA, very successfully. M1 0w-40, which is not an "EP" oil, is designed for use at up to 18000 mile OCIs in certain saab vehicles - and works very successfully.
EP is nice for having reassurance of long-life, without UOA or thinking about it. It doesnt mean that standard M1 can't do it. I'd equate it to paying a premium for M1 EP to ensure the extended OCI.
Yes they used to do that but now they don't. Maybe that is when they cheapened their formula as they used to claim 25,000 mile oil changes were possible.
Their Mobil 1 warranty claims protection during manufacturers recommended OCI...the Mobil 1 EP claims good to 15,000 miles.
ZZ, I would agree they've retracted the 25k statement. But if I remember correctly, even that "retraction" was not a retraction - they simply claimed they didn't want to go that far against OEM statements. Since then, they seem to have pulled reg. M1 into the camp of respecting the OEMs, but they caveat that by stating it's due to the warranty issues owners are facing - not based on an inadequate reformulation of M1 (which is conjecture).
On a slightly related note - I remember reading a FAQ on Mobil 5000 - driver asked "what if my OEM OCI is 10k miles". Mobil's response - "rest assured Mobil 5000 can handle it" (paraphrased, but near quote).
And another note - a FAQ on M1 HM - back when it first came out, they stated, "when first using M1 HM you might want to do a short OCI of 4 or 5k miles". They called 5k a "short OCI". I think they've since abbreviated that to a shorter distance, but it still showed their confidence in non-EP lines.
And money where my mouth is, M1 0w20 is at ~10.5k in my Mazda - with zero consumption. Will soon dipstick sample for a UOA. If the iron is > 50ppm and the TBN is < 1.0, I will retract my above post. :)
I also use M1 0w20 in my Mazda6 with no oil consumption either. I also plan on leaving it in for an extended OCI. I'll wait and see how yours did. My car loves this thin stuff, and runs so smooth with it.
There seems to be a lot a confusion about M1 EP, which is understandable. I am just a consumer, but was interested in this subject since Advance Auto Parts had them on sale for the same price, so I did some research and here is what I found out (or what I suspect):
1. The M1 EP formula changed a few years ago. Originally it was suggested by Mobil that EP could go up to 25,000 miles, but it was not API certified for most new car warranties, and Mobil specifically recommended against using it for engines still under warranty. After they changed the formula it now does meet GF-4 and API SL/CF specifications required by most new car warranties (except for M1 EP 15-50 which is a different animal), and of course it is guaranteed up to 15,000 miles (interesting to note that some other boutique oils that are guaranteed to 25,000 miles are not GF-4 and API SL/CF certified).
2. Mobil 1 EP contains 50 percent more SuperSyn than regular Mobil 1. What is SuperSyn? That is obviously proprietary, but I think it means that EP has a little more PAO/Ester and other boosted additives that are part of the SuperSyn package. The term "boosted" comes from this spec sheet:
3. There are the usual M1 bashers on this thread who say the difference is only marketing, but that is obviously bunk. The difference is not huge, and the price difference of a 5-quart jug at Walmart is not huge either, only $4 (used to be only $2.50 difference before the recent Walmart price drops). But if you are going for a extended OCI (or are willing to skip a few Biggie Fries and Biggie Drinks), it probably is worth the difference in price.