Oil Flow Rate / Viscosity and Temp

[7schulz]

How much difference in viscosity and flow rate is there between a 0w-40 and a 15w40 Syn oil @ an ambient outside temp of 50-70 deg F. This temp range is well above where both oils need to be for cold weather starts. Wouldn't they be virtually the same at that start up temp? The range for each oils usage over laps and should be the same in the overlap temp area? Or am I missing something that someone can explain to me?

So @ 0 deg one acts like a 5w and the other a 15w, and at 100 deg they both act like 40w. so at 50 deg they should both act like 20w-ish?

 

[[RT] ProjUltraZ]

but it acts like a 0W or 15W at room temperature, about 8X thicker (higher visc) than the 40W at operating temp. but that's still better than a straight 40 at room temp, which would be 30X thicker (a guess)

Widman viscosity calc

 

[BobFout]

Originally Posted By: 7schulz
How much difference in viscosity and flow rate is there between a 0w-40 and a 15w40 Syn oil @ an ambient outside temp of 50-70 deg F. This temp range is well above where both oils need to be for cold weather starts. Wouldn't they be virtually the same at that start up temp? The range for each oils usage over laps and should be the same in the overlap temp area? Or am I missing something that someone can explain to me?

So @ 0 deg one acts like a 5w and the other a 15w, and at 100 deg they both act like 40w. so at 50 deg they should both act like 20w-ish?


Essentially no meaningful difference between the two at 50 to 70*F.

Which two oils are in question? We can graph the visco at those temps to get an accurate comparison.

 

[bepperb]

"o @ 0 deg one acts like a 5w and the other a 15w, "

That's not what the W number is or how winter ratings work.

But, Bob is right "Essentially no meaningful difference between the two at 50 to 70*F."

 

[7schulz]

Like a M1 0w-40 and a Shell Rotella T 15w40 syn. Just trying to understand better. I like a thicker oil for better wear and bearing stability. Not worried about mileage implications.
If there is no difference then why would people tell me to use the 0w and not a 15w in the summer?

 

[JSP]

Here is an example:

Mobil 1 0W-40 78.3 cst @ 40C(104F) / 14.0 cst @ 100C(212F)
Redline 15w40 97.0 cst @ 40C(104F) / 14.5 cst @ 100C(212F)

At 50F I assume that difference will only be greater. Is that enough of a difference that you or your motor will notice, probably not.

 

[JSP]

For most applications you can find a 5W-40 or 10W-40 that is stable viscosity wise and that performs well, so a 15w40 really doesn't offer any benefits in most applications.

Here are the stats for Rotella T 15w40: 120 cst @ 40C / 15.5 cst @ 100C

 

[BobFout]

Originally Posted By: 7schulz
Like a M1 0w-40 and a Shell Rotella T 15w40 syn. Just trying to understand better. I like a thicker oil for better wear and bearing stability. Not worried about mileage implications.
If there is no difference then why would people tell me to use the 0w and not a 15w in the summer?


What vehicle are we talking about?

 

[labman]

If I remember correctly a purely Newtonian fluid will give a straight line plotting the log of the viscosity against the reciprocal of the absolute temperature. At lower temperatures, a small change in temperature causes a large change in viscosity. Pure base stocks are fairly close to that. Synthetics naturally won't have as steep of a curve. However, as you add VII's and other additives to one, or even a different base stock, who only knows what shape of a curve you will get. The intent is to make the curve as flat as possible, but the viscosity will still go down with temperature, but slowly with zigs and zags. With the figures JSP gave for 40 C, and the W rating, at ambient summer temperatures, I think the 0w is still going to be thinner than the 15w. It does come down to which ones. Not all 0W's are going to be the same, nor all 15W's.

 

[il_signore97]

I agree with labman. There will be a difference, and it may very well be a significant difference.

However, there will obviously be MUCH less of a difference at 50F compared to 0F, but still a difference nonetheless.

 

[Gary Allan]

If your pump doesn't slam against the relief, there will be no difference. XX cc's of fluid/sec. will be pumped. This can't account for any losses in the pump itself to whatever degree they would vary.

1) 1/2 gpm with a 100 cSt fluid

2) 1/2 gpm with a 125 cSt fluid

Both) 1/2gpm. pressure will vary.

 

[labman]

I think bypass is fairly common. Even with M1 5w30 in my truck, on a cold start up, it holds 80 psi at much above idle, but doesn't go above it as the engine speeds up. Once the engine warms up, the oil pressure goes up with engine speed. It holds about 60 psi running a steady 70.

 

[Gary Allan]

It can be for some. YMMV ..but since his question was unqualified other than temp of the fluid ..it's the answer that most fit.

 

[7schulz]

Lexus LS400 4L V8 155K Dealer maintained from new and doesn't burn.
Land Cruiser 4.5L I6 130K This engine is prone to burn oil.
Would like to get 300K-400K for both.
Looking at 5K OCI

 

[labman]

Unless you do a lot of short trips, I don't think the XW has much effect on the oil burning.

 

[daman]

Originally Posted By: il_signore97
I agree with labman. There will be a difference, and it may very well be a significant difference.
However, there will obviously be MUCH less of a difference at 50F compared to 0F, but still a difference nonetheless.

I also agree there would have to be some sort of difference at any temp,one is a syn base one is not
Originally Posted By: Gary Allan
If your pump doesn't slam against the relief, there will be no difference. XX cc's of fluid/sec. will be pumped.

again agree BUT... it's just there will be less rotating torque/power required to turn pump shaft.

 

[Gary Allan]

Yes. One will tend to pump easier. The rate will be the same (assuming aforementioned qualifiers).

 

[mechtech2]

7shultz - Your thinking is correct. At those temps, they are similar - not like at 0F or below.

Exact viscosity graphs are needed for individual oils.
Of course there will be some difference, but we are talking generalities here.

 

[CATERHAM]

The difference will be very noticeable.
While the Shell Rotella will be 53% thicker at 40C, which is a lot, the difference increases markedly as the temps drop.
At 20C (68F) the Rotella will be 90% thicker, 117% at 50F and a whopping 156% at 32F.

 

[CATERHAM]

That's a comparison between Rotella T 15w40 and M1 0W-40.