Here is the question I would like help with. Will synthetic oil allow a diesel engine to run a lower rpm’s at a gives speed in a Dodge 2500 do to its use?


Example engine is a new 2006 CTD engine, auto that use to run at 2000 rpm’s @ 70 MPH and had done so for 10,000 miles of it being driven. Now with the use of off the shelf 5w40 synthetic it now runs between 1900-1925 rpm’s @ 70 MPH. The only thing that has been done to the engine prior to this was that it the oil changed 20 minutes before it was noticed that the rpm’ had dropped between 75 and 100 rpm’s @ 70 mph. Nothing else was done to the engine or drive train to change or alter it in any way just the oil change.


So was it because of the use of the new synthetic oil that allowed it to run at the lower rpm’s or some thing else, unexplainable, BS or is it [sm=ts.gif]


[sm=thanx.gif] for any help with this question and have a very Merry Christmas,
Charles

 

I am not an expert by any means but I noticed the same thing. I have an 06 CTD with the 48RE trans and 3.73 gears. After I switiced to the Valvoline 5w-40 I noticed my RPM's dropped to 1925-1950 at 70 MPH too. I don't know if it is the difference in viscosity between the 5w-40 and 15w-40 or the difference between dino oil andsynthetic.

 

Being easier for the rotating assembly to spin due to less drag it makes sense. I will have to try that when I get enough miles on the motor ...

 

That's crazy information. I wouldnt have figured that but it sounds like it could happen.

Rudy

 

Looking at race cars, they run a windage tray to keep oil from slinging up onto the crank while its spinning which would slow it down. The synthetic being thinner and easier to sling off would in turn put less "grip" on the crank allowing it to turn easier making for easier rpm's? Im no rocket scientist and could be completely wrong (not the first time LOL) but it sounds feesable.

 

I think that there is some CTD voo doo going on here. Highway speed is a fuction of engine RPMs with constants of tire diameter, trans overdrive ratio, and rear gear ratio. The only loss is through the converter, but even in this situation, the converter is "locked" at high speed cruising.If the engine RPMs drop, then the speed of the vehicle MUST drop.

 

I'm not gonna call anyone a name..... but I can not imagine any way engine oil could effect fianl drive ratio.

 

I‘ve been called all kinds of names with this question so I’m glad you at least refrained for doing so. I too have been told it’s not possible, yet it has happened and I have seen it with my own 2 eyes. I had another person feel it was closer to a 50-75 rpm drop @ 70 mph. This is why I was asking the question if it was not from the use of the synthetic oil then what would cause it to happen when nothing else had changed to the truck?

 

Has economy increased? Could it be that the torque is staying high enough at the lower rpm tomaintain speed? I don't know either, just another guess. I'm using 15-40 Valvoline dino and I'm right 1950/70mph.

 

would if be safe to run that thin of an oil in the truck? just a thought?