Oil Change on a LML [Archive] - Duramax Diesels Forum


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brown bear
08-06-2015, 10:05 PM
I'm about to do my oil change, and I'm gonna use 15-40 regular oil
So I went to the store and the guy there told me that I need synthetic oil
because that's what's in my truck. I just wanted to know if that was true ? I have always use regular oil I'm my diesel trucks before so my questions is what type of oil is in the LML trucks? Also I want to change the oil in the transmission, is it worth to do a two flush meth so put synthetic in it? If so what transmission oil would be good for it? Thank you.

08-07-2015, 01:04 AM

08-07-2015, 06:46 AM
I run the synthetic, to get more miles between changes, but you can run regular oil. On the trans, just change the external filter every 5k and add a 1/4 quart of dex 6 to top off what came out in the filter. No need for a fluid change before 50 k unless you have overheated the trans

08-07-2015, 08:35 AM
I ran non syn. motor oil in my truck for first 20k for good break-in then switched to syn. to help in the colder temps of central Alaska. Fred

brown bear
08-08-2015, 09:10 AM
Thank you. I'm planning on using the 15-40 Mobil 1300
And gonna try the transynd transmission fluid.

08-17-2015, 08:27 PM
Do they run synthetic in lml's from the factory? I'm pretty sure that's what they told my dad when he bought his. He always get it changed at the dealer (first few are free), so I don't know what's actually in it.

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08-18-2015, 04:05 AM
More miles between oil changes reads like a good idea with synthetics, but, it does have it's drawbacks. All the greasable joints were designed in an era when you changed your oil about every 3-4 thousand miles and greased you front end etc. at that time. Going to 7-10 thousands miles intervals you are accelerating the wear of these items which need a squirt grease more often than 7-10 thousand miles...