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: new duramax owner w/questions!! dieselkidd05 10-06-2004, 11:08 PM I just ordered a 2005 gmc sierra 2500hd w/ the duramax/allison combo. i was curious as to when i should switch the oil over to synthetic? what weight should i use? i live in northern MN and it already has been dropping below freezing. this is my first diesel and i want to do it right, so could you guys out there give me some advice. thanks a lot! skoryaro2 10-07-2004, 10:23 AM I'll take this one guys - Do some searching on this site as the same question has been asked a million times (even by me in the past). You'll find lots of info. Recommended oil is 15W-40 but 5W-40 can also be used. Consensus here is to wait until about 3K miles before synthetic. That's what I'm doing with my '05. Others say you can make the switch right away but you'd be wasting synthetic oil because you should change it often during initial break-in. Bill Gisse 10-08-2004, 02:04 PM I waited to 12K and then switched to 15-40 blended synthetic/dino. Using Schaeffer's oil and fuel additive. jpekarek 10-08-2004, 06:43 PM Actually the main problem is that the engine wil not break in properly with synthetic, the lubricating properties are so good that the internals will not have enough friction to wear correctly during the first few thousand miles. That was told to me by Archie Sommer of Sommer's racing engines in Vancouver. WA. He builds the engines in my street rods and forbids the use of synthetic oils until 3-5K miles. JJs DuMax 10-09-2004, 08:01 AM He builds the engines in my street rods... jpekarek, are you turning your truck into a street rod to? Hang on baby! DK05, there is considerable discussion on syns versus dino on this and other sites. One site is bobstheoilguy.com, interesting reading. Before I forget stay away from Fram filters, you'll find intel on that as well. I have always heard and followed jpekarek's mechanics philosophy. I'm at 8700 miles on my truck, ssssssssssoooooonnnnnnnnn! I'm considering a synblend to get the best of both, better lubrication and more frequent changes at a lower cost. Still doing research though. JJ http://www.dieselplace.com/forum/smileys/smiley36.gif jpekarek 10-10-2004, 08:15 PM It's been my street rod since I bought it a few weeks ago, the Challenger and the '55 get driven a lot less now since I bought the Silverado! It pulls them to and from the dragstrip pretty well though! Edited by: jpekarek | ||