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1994 GMC 6.5L Naturally Aspirated Diesel K1500
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Discussion Starter #1
When I got to the parts store for oil the tell me to get 10w-30 for my 6.5L diesel but thd oil cap says 15w-40 which would be best option
 

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Don't trust that parts store person for anything. 15w-40 was the original and still a good choice since it look like you are in Arizona where you don't have to deal with below freezing temps. If you like synthetics or synthetic blends then 5w-40 is what those come in and are also a fine choice but only required IMHO if you need to run below freezing. Should be plenty of options at parts stores or even wally world carries quite a few options and will usually be the best prices. I think they carry Rotella and Delo which are popular big brands.
 
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1995 GMC Suburban
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There is 15w-40 Full Synthetic now available which if you are in AZ, I would suggest this one.
Check WM, they have more choices and cheaper than the part store.
 

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15W40 seems to be the choice but any brand will do.I used to use rotella T6 a lot in the past but have been buying up some mobil 1300 super 15W40 as of late.
 

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15W40 and my preference is rotella T4 + lucas or rotella T6 full synthetic.
 

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They make a 10-30 Diesel rated Rotella T5 Synthetic blend. Ive used it a couple times. Its wet just the same as the other oils...
 

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Seems like I remember being told that the 30 weights were for the Detroit 2 strokes which at one time were pretty common.
 
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The best kind of oil is CLEAN oil of the right viscosity......no matter what brand you use, it will need to be changed regularly due to soot buildup. Synthetic for extreme cold or heat, otherwise regular conventional oil is fine IMHO......
 

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2004 Chevy K3500 Crew cab DRW 6.6 Duramax
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I switched to Rotella full synthetic. I seen better mileage with it and when I had the head gaskets go, I was told that is what saved my motor from the coolant damage. I was changing it every 7000 miles. Then had the oil tested at 6000, 8000 and again at 10,000 and it came back good each time. They said I could go around 20,000 miles. I stuck with the 7000. I can tell you that if you use the Rotella T from Wallies, don't let it puddle on a smooth garage floor and step in it. There are some body parts that don't like being slammed onto a concrete floor that hard.
 
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I switched to Rotella full synthetic. I seen better mileage with it and when I had the head gaskets go, I was told that is what saved my motor from the coolant damage. I was changing it every 7000 miles. Then had the oil tested at 6000, 8000 and again at 10,000 and it came back good each time. They said I could go around 20,000 miles. I stuck with the 7000. I can tell you that if you use the Rotella T from Wallies, don't let it puddle on a smooth garage floor and step in it. There are some body parts that don't like being slammed onto a concrete floor that hard.
I run Rotella 5-40 synthetic in almost everything I own!
 

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1995 Chevrolet Silverado Z71 6.5 TD
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I run Rotella T6 in my 6.5 and Mobil 1 5-30 synthetic in my non diesel vehicles.
 

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Rotella T6 in both my diesels. My Can-am side by side likes it also
 
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