high end on R syn 5/40

[big bubba]

Members: Every morning I'm amazed at the ignorance of the person standing in front of the mirror, so here goes another......Am considering swithching to Rotella synthetic 5/40 from R 15/40 because of the flow char. in cold weather. But @ 90 degrees for 8 hrs in a hayfield, does the synthetic have comparable cushion on the 40 viscosity end comared to the dyno? After all the dyno rating is "heavier". I'll leave it to the experts. thanks bb

 

[Sully2]

Bottom line? When its "hot" a 40 weight is a 40 weight is a 40 weight.
5W-40....10W-40....15W-40.

 

[RalphVa]

A 5w40 oil will be more viscous at operating temperature than a 15w40. This is because the viscosity temperature line (or plot) on a 15w40 is steeper. Viscosity drops as temperature goes up.

This would only be true on metal surfaces that are hotter than about 212 F. At 212 F, both the 5w40 and 15w40 will have the same viscosity. The most significant difference would be at say, -40 F/C. The 15w would be like molasses; hereas the the 5w would be like a regular syrup.

Ralph

 

[big bubba]

Thanks Ralph for info...so are you saying that after warm up in summer conditions, both 15/40 and 5/40 will have the same viscosity & cushioning properties, and that the only difference will be in the winter when the 5/40 will have better flow properties? R 15/40 is proven and have broken in my new 70 HP diesel with it. I have also changed the oil at 40 degrees, and it definately is a slow flow....but the local dealer says it's okay all year round....Want to do this new engine thing right and have mortgaged 2 years of my life to purchase it....motor oils are like religion, don't know if you've chosed the right one until it's too late. thanks again bb

 

[JSharp]

Here are the datasheets for the Rotella 15W-40 conventional and 5W-40 synthetic.

http://www.shellusserver.com/products/pdf/RotellaT(CJ-4).pdf

http://www.shellusserver.com/products/pdf/RotellaTSynthetic.pdf

The synthetic is a tiny bit thinner at 100C, not enough to matter. But it has much better properties when cold. And the synthetic should hold it's viscosity better at elevated temperatures. I'd use it and not give it a second thought. The only advantage the conventional has is cost...

 

[Reg]

Ahhh, the case for a 40 weight oil...
Is there one ?

I s'pose if you have something that leaks out 30 weight oil... maybe.
I prefer an oil that flows when cold and "hurries on down" to the pan again and not hang around high in the engine.

I should add that higher viscosity does NOT necessarily indicate higher film strength, butYa all knew that already, right ?

 

[JSharp]

In engines that were designed for a 40 weight there is a case for it. But more often it seems people use it as a way to maintain oil pressure and extend the life of worn engines, or because they fall into the "thicker must be better" camp.

I'm a believer in running as thin an oil as works properly, and using synthetics any chance I can. But, that's just me...

 

[saparks10]

In engines that were designed for a 40 weight there is a case for it. But more often it seems people use it as a way to maintain oil pressure and extend the life of worn engines, or because they fall into the "thicker must be better" camp.

I'm a believer in running as thin an oil as works properly, and using synthetics any chance I can. But, that's just me...

I agree with you on the synthetics. I use Hydrotex's hyfilm max 15w-40 and average around 55k between oil change intervals, with an oil analysis program of course. I also have several truckers that swear by it and average over 60k. I pull an oil sample for them as well. It's a group 3 severly hydrocracked and hydrotreated synthetic oil, vs. rotella which is a group 2 synthetic.

 

[DieselPower]

Where might you have heard that Rotella synthetic is group 2? By the way, group 2 base stocks are NOT synthetic. Synthetics start at group 3.

 

[rdam]

Bubba,

Does the owners manual call for a 40 weight? I have a much smaller Kubota tractor, but the owners manual calls for 10W 30, and that's what she gets. Dino until 100 hours, then I'll switch to a quality synthetic 30 weight which meets the specs in the manual.