5w40 Syn and 15w40 any type.

[Sushibar]

Why do most "big oil" companies have a 5w40 syn and not a 15w40 synthetic. I have delvac1 5w40 right now in my ford 6.0l and runs the best ever. Am I hurting anything by using this weight. I understand it is still a 40 weight at operating temp. But why the different weights when cold. Synthetic vs dino. And I know others make a 15w40 Syn. but could someone explain to me why the they use the 5w40.

 

[Stewart Fan]

A 5w is going to flow better than a 15w when its cold. Synthetic or otherwise.

I have a Cummins in my Dodge. Cummins recommends a conventional 15w40 for all but the coldest conditions. IIRC anything lower than 0 degrees they recommend a 5w-40 synthetic.

If you want to run synthetic year round it won't hurt anything. I've seen a bunch of UOAs for the CTD and it seems the be pretty easy on oil.

Since a cold night down here near Seattle is about 25-30 degrees I won't be running synthetic.

 

[Terry]

Because a 5w40 syn could be a 15w40 if tested that way. Dirty little secret that many here don't seem to remember is that a syn oil can be technically a straight weight and a 10w30 ( amsoil) or many other combos and be sold as different products for PROFIT....

I note a popular fuel additive seems to have started doing that here recently...

 

[Steve S]

Quote:

---

Because a 5w40 syn could be a 15w40 if tested that way. Dirty little secret that many here don't seem to remember is that a syn oil can be technically a straight weight and a 10w30 ( amsoil) or many other combos and be sold as different products for PROFIT....

I note a popular fuel additive seems to have started doing that here recently...

---

'splain the fuel additive thing to us.

 

[simple_gifts]

Quote:

---

splain the fuel additive thing to us.

---

Perhaps he is referring to FP3K, FP+ for diesel, FP+ for gas

???

 

[another Todd]

Unless you check the specs, you don't know what you are getting anyhow. Case in point---Amsoil 15-40 vs. Rotella T Synthetic:
Amsoil Vis. @ 40 C. is 89.7
Rotella Vis @ 40 C. is 90

Amsoil Vis @ 100 C. is 14.4
Rotella Vis @ 100 C. is 15

They are basically the same weights yet one is a 15-40 the other is a 5-40.

 

[beanoil]

Interesting observation Todd. I did a little checking, for example:
QS 5-30 has very similar rates to another vendors 10-30, and similar rates again to another vendors 5-20. I assume base stock has a lot to do with both the viscosity rating, and it's spread across the temperature scale. I wish there was a better way of determining what happens outside of the scale?