Rumor about not using synthetic in a CTD got started years ago, when some Cummins dealers advised their customers not to use synthetics during a 15K break-in period - supposedly synthetic oil prevented the cylinder-walls from wearing past the cross-hatch bore pattern. After 15K, it was supposed to be OK to use. My understanding is that Cummins asked their dealers to stop that recommendation.

I used to run Mobil-1 at $23 a gallon, until the Mobil-Exxon merger made it hard to get, and there were strong claims that the formulation was changed to a semi-synthetic base stock. I now run Shell's Rotella from Wally World, for $15 a gallon, which did quite well in last summer's 105F heat, and last winter's -25F cold. Rotella seems to carry the soot noticeably better than Mobil-1; takes a couple of thousand more miles to foul to black. Can't see using a non-synthetic, considering that price.

 

There's no reason other than cost to avoid synthetics on a 5.9 Cummins.

I'm a big fan of synthetics, but regular oils are so good now that it's hard to make a sound financial argument in favor of synthetics in the Cummins.

That said, extreme cold temps can make the argument for syn easier to make. I'd much sooner justify it to a Canadian than a Floridian. You don't need synthetic in Miami!


Now with diff oil, trannies, etc, it's strongly in the syn camp's favor. But engine oil isn't nearly as clear an advantage, imo.

I'm a big fan of Delo 400. I run it just about every engine I have...

Justin

 

So, does anyone have a personal experience with a 100+k miles truck starting to leak if switched to synthetic?
-P

 

I'm looking to extend the life of my engine as long as possible. Synthetic handles the higher pressures found in a diesel I'm told. I use the Mobil 1 Truck/SUV in my engine and in my trans. It does make the trans shift better also.

Edwin

 

Doesnt synthetic have a higher flash point too?
Any downside (other than cost) from going from delo 400 to royal purple 15/40?

 

I us syn and do a filter change every 10,000 kms for about 3 of them. That part of the engine is good. Use syn throught the system.

 

If this happens, it's because your sludge was forming a "false seal".

 

I just got my diesel power May newsletter via email. It has some interesting stuff about oil in it. It is 3 pages long but if some of you would like to read it let me know and I can email it to you or maybe even post it.

 

I put it in my 89 at 85000 miles. The side covers that had been leaking with Rotella sealed up and never leaked again.

 

I'd liek to read it if you'd email it to me...

 

pm me your email and I will send it over.

 

Anyone living in an area that gets below 30F, SYNTHETIC is the way to go, hands down. The flow is much better than conventional and cranking times is reduced.

I am going to Mobil 1 Synthetic once I hit 15K.

 

I went with amsoil 15-40wt just as soon as I brought my new used 94 CTD home..at 205,011 miles ..NO problem...and if it did start to leak I'd just fix it anyway..I hate oil leaks..!!! been using synthetic's since 1978..every thing I own that runs on diesel or gas has amsoil..lawn mowers,chain saws,snowthrower..!! Mobil 1 is great too !

 

I use Schaeffer Supreme 7000 15w40 but I change my about 18,000 miles and no problems,

 

354,000 here running Amsoil synthetic, no leaks that I would attribute to the syn... Did replace the valve cover seals 100,000 miles or so ago, but then again they had been reused several times after valve adjustments.

As many others have stated already, if you're in a cold climate syn is the way to go. Those snowmobile trips to Northern Maine with -30 degrees F starts without a block heater need all the help we can get.