I apparently don't understand oil weights

[LittleBill21]

yea lou , they have 2 different temperatures listed, for 40 weight, that was the point of my question.

 

[LouNY]

One is a 10W-40 the other is a 15W-40 that is the difference for the low end.
They are two different oil specs.
That chart is just listing recommended oils for different ambient temperatures.

 

[LittleBill21]

yes but the chart is showing a difference for the upper end, with both being 40 weight, thus the point of my post.

 

[LouNY]

Not really it is showing different oils for different ambient temperatures;
for an ambient range of 0F to 80F they recommend either a 10W-40 or a 10W-30;
change the ambient range to 10F to 100F they recommend a 15W-40.
For operation below 10F down to 0F then want a multi grade starting point of 10W,
for operation up to 80F the upper end can be either 30 weight or 40 weight,
once the ambient gets above 80F they desire a 40 weight.
The 40 weight is good for 80F OR 100F ambient operating temperature.

None of these temperatures are of the oisl they are the operating condition temperatures.

 

[CADplans]

The way I was taught, (was a long time ago, it may be wrong,,)
is that the multi weight oil is,,, something like the following;

5W-30 oil is 5 weight oil.
that oil is 5 weight at "room" temperature.
As the engine heats the oil,, long chain molecules that are relaxed at room temperature curl, and become more rigid, making the oil act like 30 weight as the engine temperature rises to operating temp.

If that explanation is correct, the original chart makes sense.
5W-30 oil is 5 weight oil
10W-30 oil is 10 weight oil
15W-30 is 15 weight oil
The lowest temp for an engine would be colder for 5 weight oil as compared to 15 weight.

When did I learn this stuff? I put 5W-30 oil (I am not naming the brand) in an air cooled Kohler engined garden tractor. As soon as the engine warmed to operating temp, it looked like I was fogging for mosquitoes,, smoke was billowing out of the exhaust.

Well, the 5W-30 oil modifiers could not withstand the air cooled engine operating temp..
(air cooled engines operate at higher temps than water cooled engines)
The modifier molecules broke down, the oil reverted to 5W,, the thin 5W oil went right past the piston rings,,, =smoke!! (that year was 1980,, multi-weight oil was pretty new, IIRC)

I changed the oil to the recommended Straight 30 weight that was recommended, the engine ran fine for the next 20 years.

AFAIK,, the modifier molecules are more able to withstand high temps now,,
Air cooled engines can operate with current multi-weight oils, now.

 

[BigBlue1]

The way I've always understood the numbers is like this:

The first number is the "flows like XX at winter temps". The second number is the "protects like XX at operating temperature".

Take, for example, 10W-40. So, 10W-40 flows when cold like a 10 weight oil. And protects like a 40 weight oil at operating temp. Both numbers are important because engine temps at full cold start will influence the oil flow in an engine. Using a straight 40 weight may starve the engine of oil if it was designed for 10W-40, even though they will protect the same at operating temp.

This is simplistic and I'm sure not accurate enough for the finicky fact-checkers but it gets the point across.

As for charts, refer to the manual for your vehicle or equipment to know what is required at any particular temp range. Engines are not all the same and you can't assume the effects are the same across various engines. And as Lou points out, the temp ranges in the manuals are for ambient air temps, not engine operating temps.

Rob

 

[RalphVa]

The way I was taught, (was a long time ago, it may be wrong,,)
is that the multi weight oil is,,, something like the following;

5W-30 oil is 5 weight oil.
that oil is 5 weight at "room" temperature.
As the engine heats the oil,, long chain molecules that are relaxed at room temperature curl, and become more rigid, making the oil act like 30 weight as the engine temperature rises to operating temp.

If that explanation is correct, the original chart makes sense.
5W-30 oil is 5 weight oil
10W-30 oil is 10 weight oil
15W-30 is 15 weight oil
The lowest temp for an engine would be colder for 5 weight oil as compared to 15 weight.

When did I learn this stuff? I put 5W-30 oil (I am not naming the brand) in an air cooled Kohler engined garden tractor. As soon as the engine warmed to operating temp, it looked like I was fogging for mosquitoes,, smoke was billowing out of the exhaust.

Well, the 5W-30 oil modifiers could not withstand the air cooled engine operating temp..
(air cooled engines operate at higher temps than water cooled engines)
The modifier molecules broke down, the oil reverted to 5W,, the thin 5W oil went right past the piston rings,,, =smoke!! (that year was 1980,, multi-weight oil was pretty new, IIRC)

I changed the oil to the recommended Straight 30 weight that was recommended, the engine ran fine for the next 20 years.

AFAIK,, the modifier molecules are more able to withstand high temps now,,
Air cooled engines can operate with current multi-weight oils, now.

Wrong. The lower temperature oil rating is not determined at room temperature. It's at various temperatures, generally very cold and is different for 0w, 5w, 10w, 15w.

5w30 is NOT 5 weight oil. It is 5w at its measured low (cold) temperature but is 30w at operating temperature of 212 F. And so on for the other oils mentioned. The second # is the operating temperature of the oil. The first # is the weight at some cold starting temperature, which is different for 0w, 5w, 10w, 15w.

Those upper temperatures for each oil are for air cooled engines, not water cooled ones.

Ralph

 

[RalphVa]

Here's the chart that shows what temperatures the lower # of oil viscosity is measured at. It's a rotating viscometer that measures in cP (centipoise or poise) vs. the upper (operating temperature) value that is measured in cS (centistokes) @ 100 C (212 F).

 

[CADplans]

Wrong. The lower temperature oil rating is not determined at room temperature. It's at various temperatures, generally very cold and is different for 0w, 5w, 10w, 15w.

5w30 is NOT 5 weight oil. It is 5w at its measured low (cold) temperature but is 30w at operating temperature of 212 F. And so on for the other oils mentioned. The second # is the operating temperature of the oil. The first # is the weight at some cold starting temperature, which is different for 0w, 5w, 10w, 15w.

Those upper temperatures for each oil are for air cooled engines, not water cooled ones.

Ralph

I see this as an explanation,,,,

multigrade oils are typically created by blending a low-viscosity base oil with VI improver additives (see the additives section of this book). For example, when these polymer additives are blended in the correct proportion with an SAE 15W oil, the oil flows like an SAE 15W oil at low temperatures and like an SAE 40 oil at high temperatures. The result is an SAE 15W-40 viscosity grade oil that will provide wide protection over an extended temperature range.

 

[Diggin It]

This is from my generator Install (left) and Operator's (right) manuals. If 5W30 is supposedly only good below 50F, why are they spec'ing it for all temperature ranges?

Also note, they supply 'organic' oil, but recommend synthetic.