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This thought has crossed my mind a few times and decided to toss it out on this site for your opinions. I see a number of people (on BITOG) switch to M1 products (gear oil, syn. PCMO, etc) and they run it for a short interval but when they do their first drain they are horrified by the darkened color. I've seen a lot of people talk about trying M1 gear oil once and saying it oxidizes fast. Being it was a 'used' system there is some build up of slugde and other material, what if it's just the ester co-base in many of their products doing some cleaning and not really oxidation? I would imagine if this is the case they could ran the oil over a few intervals and it would start to clear up. I haven't seen any UOA's with an oxidation (and TAN) test to prove otherwise. If someone added (here's where I would get slapped around on the other site) ARX in their gearbox or rear end they would expect the oil to come out dirty. I'm just wondering if some people are jumping to conclusions because of what expectations they have. I might switch the gearoil in my truck to M1 and have the local lab run a test on it. It will be awhile but I might go ahead with that.

What are your thoughts on people jumping to conclusions about M1?
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I think you are correct in your assumption. Mobil 1 uses Group III/IV and V base oils. Varying amounts for different grades. Mobil 1 EP was the only grade to show Group III. Mobil 1 keeps an engine VERY clean.

Here is the kicker, Amsoil's own testing of PCMO's, MC oils and Gear oils has Mobil 1 at #2 for all three tests. In some of the tests, they scored 1st.

I want the oil to get dark, it means it's doing it's job. I was told by someone familiar with Delvac 1 and Mobil 1 0w-40 that both contain significant group V content fwiw.
I've been running Mobil 1 for extended drains in two of our vehicles for years with excellent results. The 5.2 in the 2000 Ram 1500 recently returned an excellent UOA after 10k miles with 5w-40 TSUV. Blackstone's significant comment was "we're glad you didn't drain the oil yet..." It'll be going to 15k miles.

The 5w-30 EP in my wife's Sebring 2.7 went 15k miles, recently changed at that interval. No issues, lower than average wear #s on the UOA, although it was almost time to change.

No complaints about Mobil-1 here. I'd say it is rated well for my purposes.
I don't doubt Mobil is a good product. I think people know just enough to put blinders on or not be able to see the whole picture. To me the first time I heard about M1 gear oil oxidizing under 10k in a truck seemed strange when their conventional was just fine. The first thing I thought of was the esters doing cleaning and second I know it is tougher to oxidize a PAO/di-ester based product than conventional. So I was skeptical of the 'color' test and of course some use their nose which is a bad test all around.

Thanks for the feedback...
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