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Hey all . At 1200 miles now on my L5P and looking to do my first oil change pretty soon. I heard a lot of mixed things about whether or not to switch to synthetics this early in engine life.

Due to Connecticut semi-cold winter coming , I figure a 5-40 would help me out with those cold starts (especially considered they cut my block heater cord out and don’t have a resolution yet) Only problem is I can’t find it in a non synthetic. Or would the synthetic be fine? I know how some of you old school guys are lol. Thanks !


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Back when synthetics first came out for automotive use the manufacturers wanted you to run conventional oil for what they called the break-in period and the things you hear are a hold-over from those days. With changes in manufacturing procedures, materials used and so on many vehicles now come off the assembly line with synthetics in them and if you're doing a factory order you can usually order your vehicle with synthetics. I run what came in the engine until the first oil change and then change over to synthetics and have been doing that for years and have never had a bit of trouble. My vehicles last forever. I have a 1987 Chevy van that I handed down to my kids and when I had it I drove all over the world with it, including 5 years in Germany and autobahn driving. It has never had a wrench on the engine other than a water pump change. I use oil analysis (and used to run an oil analysis lab) and if there was a problem like the old days where rings might not seat I'd see it in the oil. I haven't checked on the newer trucks but when I changed over in my LBZ the warranty wasn't impacted - as a matter of fact the changeover to synthetics was a service the dealer offered. If you want to be 100% sure, check your owners manual and warranty info and check with your dealer to verify the warranty won't be impacted by synthetics.
 

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My first Dmax never would get any fuel mileage. Conventional wisdom on the forums said I should not have put synthetic in it on the first oil change like I did. Sure you can run synthetic from brand new and the protection is there but will everything break in properly? I run plain jane old Rotella 15W-40 now and just had my LML apart for a burnt piston at 244k miles. Everything inside looked like new. All the original hone marks were still in the cylinders, clear to the top of the bores. The rod bearings and crank still looked like new. So if these things won't even break in properly with conventional oil, synthetic may only exacerbate the issue. After what I just saw in my high mileage engine, I don't know if I'll ever switch to synthetic since my oil is less than $10 a gallon. The synthetic oil will gain you some fuel mileage but maybe or maybe not enough to offset the additional cost. It should also allow you to extend oil change intervals if that's your intent. As for cold weather starting on 15W-40, as long as the glow plugs are working, you won't have anything to worry about it, especially if you intend to plug it in. My old LML was starting down to about zero last winter with 3 bad glow plugs. It was a bit rough for a few seconds but still started, no problem. Looking forward to this winter with 8 good plugs, should start like a new one!

Oh, just saw you don't have a block heater. Still don't think you'll have an issue.
 

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"Starting" in cold weather isnt the issue.

Oil flowing in cold weather is.....

https://www.youtube.com/watch?v=paXIdeB75V8
Oh I hear ya. 15W-40 will flow well enough in the lower 48, it's been doing it in HD diesels for decades with Rotella having been the go-to oil in millions of trucks that ran hundreds of thousands of trouble free miles on it. I start mine nearly every day whether it's 115 degrees out of 30 below and at a quarter million miles the bearings were beautiful. Real world results.

But hey, it's America. If guys want to spring for the synthetic, more power to them! I'd run it for improved fuel mileage and extended oil change intervals except for one other issue. I got tired of finding the foam rubber seal on my air filter sucked in and allowing unfiltered air into the intake. I haven't said it for a few days so here goes again - the stock air filter boxes are junk! Also, an air filter wouldn't last a 10k mile oil change without substantially affecting my fuel mileage so I changed to an oiled filter. It improved my fuel mileage, requires less maintenance and saves me money on air filters. However, I'll allow that it doesn't filter as well as the OEM paper filter. So I elected to keep running conventional oil due to the cost and stay with 10k mile oil changes to keep the Si levels in my oil from building up too high. Which reminds me, it's about time to run an oil analysis.
 
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