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I have purchased my first diesel. 2018 GMC 2500HD. I have always used Mobil 1 synthetic in my gas trucks. I am very confused about what would be the BEST oil for my new diesel. I stress BEST because I don’t care about the cost. I see in my manuel that it needs to be 15w 40. I haven’t been able to find 15w 40 Mobil 1. Should I be using synthetic or one of the oils I am seeing that is designed for diesels? Any information would be appreciated.
 

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Welcome to the site and congratulations on the new truck.

As for the best oil, you will get many opinions. Always check to see that the oil you choose meets the requirements set by the mfg of the engine. I don't remember what the new specification is, but it was CJ-4 at one time. If they oil you choose does not meet the specifications, it may not have the proper additives to help with soot control and wear in the engine.

Lots of people like Schaeffers, Mobil Delvac, Delo, and the list goes on. Don't be surprised at how many different opinions you get. Also try searching the forum for oil recommendations.
 

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I have a 2004 Duramax LLY engine with 81,000 miles. I have always used full synthetic in it, and currently use Mobil Delvac 1 ESP synthetic oil. You can get it in either 15W-40 or 5W-40. I have been using the lighter stuff in my truck and it has been great oil. You can find it at NAPA, Pep Boys, and O’Reilley’s. It costs about $32.00 a gallon.
 

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I'm downunder in Australia.....and I use Amsoil Premium Diesel oil 15w40.

I also have a Amsoil remote head unit with bypass filtration. I have my oil analysed every 10,000klm (6,000 miles?). So far, since fitting this system @ 114,000 klm on the clock I've had two analyses done and the oil is still excellent @ 140,000klm.

Roachie,
Kadina SA
Australia
 
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I have purchased my first diesel. 2018 GMC 2500HD. I have always used Mobil 1 synthetic in my gas trucks. I am very confused about what would be the BEST oil for my new diesel. I stress BEST because I don’t care about the cost. I see in my manuel that it needs to be 15w 40. I haven’t been able to find 15w 40 Mobil 1. Should I be using synthetic or one of the oils I am seeing that is designed for diesels? Any information would be appreciated.
The full synthetics are not 15w 40. They are 5w 40. There are several to choose from. There is nothing wrong with Mobile 1 5w 40, it is a fine oil.

I use Shell Rotella T6, also full synthetic, because in my area the cost is less. As long as I am getting a comparable product, why not spend as little as possible.

There are other oils out there equally good but I find the local availability is why I went with Rotella too.

I do use Mobile 1 in my differential.
 

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Another vote for Amsoil. I have been running it in my truck since 800 miles. I run their Signature Series Max Duty 5W-40, but they also have a 15W-40 version for warmer climates. They just changed the name from Premium Diesel, which Roachie is referring to, to Signature Series (like their line of oils for gassers). They stock it at my local NAPA along with the Amsoil filter for the Duramax.
 

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Don't waste your money on the expensive snake oil brands, the Duramax is the easiest on oil out of the LT diesels and will run like clockwork regardless of the brand you use.
 

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Any name brand that you can get easily locally is best.
 

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oil is uhm oil. i have not seen or heard of any issues relating to oil brand, throw 15 40 rottela in and roll. you will not notice a different in brands.
 

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I have purchased my first diesel. 2018 GMC 2500HD. I have always used Mobil 1 synthetic in my gas trucks. I am very confused about what would be the BEST oil for my new diesel. I stress BEST because I don’t care about the cost. I see in my manuel that it needs to be 15w 40. I haven’t been able to find 15w 40 Mobil 1. Should I be using synthetic or one of the oils I am seeing that is designed for diesels? Any information would be appreciated.
I have the same truck .The dealer uses Mobil One .I can not fine 15-40 in Mobil 1 so unless ull Synthetic.The Best one the make. they know something I do not. I do it myself now. I used Ams Oil 15 /40 .The best one they put out.With a Wiks Filter,I see these new Ams Oil Filters.Like to try one.IIt cost me wityh my Super Ams Oile Dealer Discount like $165.00.00.Not Cheap. I am going to try Shell Rotella T5 as it is $17.99 a gallon wit a Fram Filter.I will change at 7500 miles instead of 10,000. I hope thos helps.If you live where it is under 30 dgrees F everyday in the winter.You can use a 5 / 40 . Over and Out.:cool:
 

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I have the same truck .The dealer uses Mobil One .I can not fine 15-40 in Mobil 1 so unless ull Synthetic.The Best one the make. they know something I do not. I do it myself now. I used Ams Oil 15 /40 .The best one they put out.With a Wiks Filter,I see these new Ams Oil Filters.Like to try one.IIt cost me wityh my Super Ams Oile Dealer Discount like $165.00.00.Not Cheap. I am going to try Shell Rotella T5 as it is $17.99 a gallon wit a Fram Filter.I will change at 7500 miles instead of 10,000. I hope thos helps.If you live where it is under 30 dgrees F everyday in the winter.You can use a 5 / 40 . Over and Out.:cool:
Sorry for the typos .Holy Cow.Dealer uses Mobil 1.I do not trust them.I used Ams Oil. Expensive . I am trying Shell Rotella 5. $ 17.99 a gallon . I hope u understand that one.Phew.o_O
 

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Shell Rotella T 6 is another Full Synthetic a step up from T5 and $ 44.98 a gallon a 3 gallons. Or two gallons and 2 plus quarts.Need a little extra for a larger filter.If you go Ams Oil . It is the Signature Series. They make a Large Capacity Filter. Supposedly keeps oil clean for a while.Like to see that. The filter is $ 45.00. Again Ams Oil runs about $ 165.00. Rotella 6 about $ 140.00 .Rotella 5 $ 65.00.
 

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You might look at the diesel oils that Hot Shot's Secret offers. Most synthetic diesel engine oils are Group III, with semi-synthetics being a mixture of Group II and Group III oils which are all refined petro crude oil.
Group IV and Group V oils are usually PAO (poly-alpha olefin) which are pure synthetic motor oils.
HSS offers different types of diesel engine oils to meet various needs. Sounds like their Blue Diamond PAO oil would be your choice. I have used their products for years and very pleased with their performance.
 

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The full synthetics are not 15w 40. They are 5w 40. There are several to choose from. There is nothing wrong with Mobile 1 5w 40, it is a fine oil.
Oh yeah?





 

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Oh yeah, the only oil brand that you have listed that has PAOs in it is the Redline. The Redline oil is a blend a not a full PAO oil like HSS Blue Diamond.
All the oils listed are great products, I have used Shell Rotella myself for decades, but decided to use a product produced by an American owned corporation.
Oh yeah?





 

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Shell Rotella T 6 is another Full Synthetic a step up from T5 and $ 44.98 a gallon a 3 gallons. Or two gallons and 2 plus quarts.Need a little extra for a larger filter.If you go Ams Oil . It is the Signature Series. They make a Large Capacity Filter. Supposedly keeps oil clean for a while.Like to see that. The filter is $ 45.00. Again Ams Oil runs about $ 165.00. Rotella 6 about $ 140.00 .Rotella 5 $ 65.00.
Not sure where you are getting oil, but you can get Rotella T6 15W-40 for $20 a gallon at Walmart. That and a Mobil 1 M1-303A filter at about $10 and my oil changes are about $70 total.
 

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Oh yeah?





Those are "synthetic" only because the USG allows them to say it due to old litigation back in the infancy of Mobil 1. In truth the ones you have listed are all super refined Dino with a lot of additives. :) :) Do not feel bad most people do not understand or care but the facts are what they are. Do the research yourself and find out.
 
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