Synthetic oil or Conventional oil?

[H2Oman]

What do you recommend and why?

I have had problems with Turbo cars in the past when using Conventional oil and so I am thinking about using Synthetic oil in my 6.4.

[OMCUSNR]

I can't justify the cost of synthetic w/out going to extended drain intervals. I live in a relatively mild area, and I run 15W40 all year in my 6.0. It doesn't have any problems, and I've been changing at 7 to 7.5k over the 66k life of the truck. I use Delo 400 CI (now CJ) and pull OAs at every change to track fuel dilution. It shears, but the truck runs great, and the OAs have come back with good wear numbers. I don't think the 6.4s are having the romping / surging problems the 6.0s have, but in cold weather it might be good to drop to a 5W40 syn.

There's nothing wrong with either type of oil, just depends on what your needs are, and how much money you have to spend on maintenance. The modern "conventional" oils are great for turbos (give them about three minutes to cool down after a hard run), and the new CJ is formulated to carry the soot w/out problems.

Regular oil is about 1/3 the cost of synthetic though.

[montanafan]

The "Chief" is right. Your turbo problems were not oil related unless the turbo was not getting proper oil delivery. There are thousands and thousands of turbocharged trucks, large and small, plus many cars on the roads that have never used anything but conventional oils and have had 0 problems.
Oil choice is personal. All the oils that meet your engine's required API and viscosity are great oils.
Many here use syn 5-40 in the winter for easier cold weather starts.

[JOHNNYWEB]

all oils are not created equally. other wise they would all be the same price. i am i big fan of the amsoil 15/40 h.d. diesel oil i run it in both my super dutys and have had alot of trouble free miles. usually a synthetic oil will stand up better to high heat situations (like turbo lubrication) and mantain there viscosity in high heat.i also like the 15k drain intervales 14 qrts of oil sucks to drain and get rid of. the rest of the fluids specified for your truck are synthetic so why not do the engine as well. im not sure what dello cost these days but im paying like $16-17 per gallon for synthetic. that is also because i have a wholesale account set up at amsoil but any way i use my truck pretty hard and like the fact i put the best oil i can in there to protect it. just my 2 cents on the sublect.

[RNGMSTR]

I wouldn't use the 15/40 in your 6.4, if you choose amsoil, they have a 5/40 (deo) oil for the cj-4 requirements.

[Gary Hill]

I have asked before and never heard a comment. Growing up my dad and grandfather always used Marvels Mystery Oil in their crankcase and fuel. I see the label saying it does not meet new emmisions. Is it a problem to mix into the crankcases anymore on these new trucks. I have used it for years in my own stuff. Comments...........

[Stealth03TDI]

Mobil now has a full synthetic Delvac 1 ESP 5-40 that is CJ-4 certified. It meets the major engine msg specs (cummins, cat) but I didn't see interntional. Anyone have any experience running or hear anything? Hate to cause damage to the engine and find later it was an unapproved lube.