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Discussion Starter #1
This is probably not a new question but since I Am new to the forum and new to diesels and want this thing to last a very long time. The question is--Should I use synthetic oil to prolong engine life or should I stick with GMC recommended regular oil?


Then--what kind of oil is best for the Duramax? Thanks in advance for the information.
 

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Synthetic after about 5,000 miles. I like Amsoil full synthetic 15w40 diesel oil. I ran synthetic in my last 350/5.7L gasser and had zero blue smoke at 170,000 miles. Also, change rear differential to synthetic at about 5,000 miles.


Others with more knowledge will chime in I'm sure....
 

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Syn oils are better, there is no debate.


However, the more type A among us still feel better chnaging the oil at "low" mileage intervals. It's fine if you feel that way, you have invested a lot of money and there is no such thing as maintenance that was done too well, but don't waste your money on a syn oil.


Syns are designed to run longer in engines and with a good regiment of oil analysis you can double the recommended oil change interval. Oil analysis is also a good idea because it can spot other maintenance problems early such as head gasket leaks and air filter problems.


Let all the components of your Dmax break in to the proper levels and then syn from bumper to bumper!
 

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The thing with diesels is they tend to load up oil with soot. A good syn oil will be no where near breakdown by the time it's loaded with soot to the point where it should be changed. I run Dyno oil and change it every 5,000 myself. IMHO to get the full benefit of syn oil you need to have better than stock filtration to allow the oil to remain in the crankcase long enough for it to make economic sense.


But then I live in the south and do not need syn's cold flow charcteristics.
 

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Discussion Starter #6
Thanks for the help guys,
It appears that going syn is the way to longevity. I have 13,000 on my rig so far, so better get the changes done.


Still confused as to what kind of syn to put in the engine. I like to change at least every 5,000. 4,000 usually. Thanks again for the infor. This forum is great for us newbies.
 

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While the oil in my 20 year old Mercedes sedan gets very sooty very fast, the modern Bosch FI system in my Duramax leaves the oil no sootier in appearance than oil in a gasser at equivalent mileage.


I am using Shell Rotella synthetic 5w-40 and changing every 6K miles.
 
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