FAQ - Thin Oil Myth

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FD777

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I created this to clarify the myth that "5w-30 and 0w-30 are too thin!"
This was originally a supplementary write-up for my GC FAQ.

If you see any errors or have suggestions, please PM me.
(I'm sure there's room for lots of improvement.)


Thin Oil Myth
Created: April 10, 2006
Last Edited: Never

Disclaimer:
All the temperatures here are in celcius.

Short answer:
0w-30 and 5w-30 can be thicker than 10w-30.

Long answer: Read below.

Really Basic (but not so intuitive) information:
  • I'm sure we have all seen 5w-30, 10w-30, 10w-40, 20w-50, but what does it mean?
    When talking about viscosities, you must state the temperature.

    Lets break this up into two categories: hot and cold.
    • Xw-20, Xw-30, Xw-40, etc (HOT!)
      This is your oil's hot viscosity. The viscosity is measured @ 100c.
      This number is relative when the engine is warmed up.
      The most common unit is cST. The larger the number, the "thicker" the oil.
      • Examples
        A "30" weight is between 9.30-12.49 cST @ 100c.
        A "40" weight is between 12.50-16.29 cST @ 100c.

      Here's a table.
    • 0w-XX 5w-XX 10w-XX, etc (COLD!)
      This is your oil's cold viscosity. A 0w, 5w, 10w, etc, are not measured at the same temperature!
      This is number relative when starting your engine.
      The most common unit is cP. The larger the number, the "thicker" the oil.
      • Examples
        A "10w" weight must have a MAX viscosity of 6600 cP @ -30c
        A "0w" weight must have a MAX viscosity of 6200 cP @ -35c

      Here's a table.
  • It never gets to even -15c here, so what's the start up viscosity for me?
    Great question! A lot of us don't live in super cold temperatures.
    Unfortunately, the oil companies don't have to tell you. All they need to specify are the extremes.
  • Can I know an oil's viscosity at different temperatures?
    Yes! Aside from actually measuring the viscosity, you can do some calculations.
    With a viscosity calculator and enough data, you can piece a graph together.
    You can usually get all the data from the manufacturer's datasheet.
    Take the calculator with a grain of salt. They are decently accurate in most temperatures, but I wouldn't trust them below -15c.
  • Why do they measure the cold and hot viscosity (cP vs cST) in different units?
    Something about dynamic vs kinematic viscosity.
    I won't go into detail here, because I haven't researched this.


Back to the point, "Why isn't 5w-30 or 0w-30 thin?"
I think a real-life example will help.
  • Lets compare Mobil1 5w-30 to Mobil1 10w-30.
    • First the Hot (100 c) setting
      Straight from Mobil1's datasheet (Looked on April 4, 2006):
      • 5w-30 = 11.3 cST
      • 10w-30 = 10.0 cST

      Looks like the 5w-30 is thicker! (Notice how both oils are a "30" weight)
    • Now lets look at the cold setting
      Based on the 5w and 10w specifications:
      • 5w-30 = 6600 cP or less @ -30c
      • 10w-30 = 7000 cp or less @ -25c

      Looks like 5w-30 is thinner than 10w-30!
  • We can conclude that:
    • 5w-30 is thinner than 10w-30 at -25c.
    • 5w-30 is thicker than 10w-30 at 100c.

    The above implies that 5w-30 thins out less than 10w-30 as temperature increases.
  • Still confused? Maybe this graph will help.
    The graph is just a learning tool, don't use it as an actual reference.
  • Reminder: this example refers to Mobil1. If you're curious about other brands, you will have to look at their datasheets.


Finally, my concluding remarks.
  • My main points are:
    • 5w-30 can be thicker than 10w-30.
    • 0w-30 can be thicker than 5w-30.
    • Unless you have tools to measure viscosity, you need to at least:
      • Specify a temperature.
      • Check the manufacturer's datasheet.
    • The cold viscosity tells you NOTHING about the hot viscosity.
  • Some things you might have noticed:
    • I haven't claimed an Xw-30 to be thicker than an Xw-40. At least at operating temps, any Xw-30 will be thinner than any Xw-40.
    • Everything I have said can apply to other weights within the same hot viscosity.
      • It's possible for a 0w-40, 5w-40, or 10w-40 to be thicker than a 15w-40 at certain temperatures.
      • It's possible for a 0w-20 to be thicker than a 5w-20 at certain temperatures.
  • MANY other factors about oil were not discussed here. Please don't base your oil preference on viscosity numbers only.
  • When in doubt, follow your car's manual. At least you won't void your warranty that way.


Credits:
  • BITOG, 'nuff said.
  • AndyH for the cold viscosity table.
  • 427Z06 for the calculation info.
  • The countless number of names I have forgotten.

Thanks for reading!
 
good job but remember that data sheets are ALL typicals and they WILL vary.

and a 30wt at 10.0 cSt vs a 11.0 cSt is not a big deal IMHO.
bruce
 
"Celcius" is found abundantly on the internet. However, the unit "Celsius" is used to describe the "centigrade" scale. It was named for Anders Celsius who dived the range of temperature from freezing to boilng into 100 divisions. He was a Swedish astronomer that lived from 1701 to 1744.

For completeness, Gabriel Daniel Fahrenheit invented the first accurate thermometer. The Fahrenheit scale is named after him.
 
quote:
I wasn't sure about the if it was Celcius or Celsius, now I know.
Click to expand...
Maybe you were thinking of Paracelsus.
cool.gif
 
quote:
Originally posted by GMorg:
"Celcius" is found abundantly on the internet. However, the unit "Celsius" is used to describe the "centigrade" scale. It was named for Anders Celsius who dived the range of temperature from freezing to boilng into 100 divisions.
Click to expand...
Anders Celsius range went from 100 (freezing) to 0 (boiling)
It is often claimed that Carl von Linné (Carolus Linnaeus) instigated the reversal, but it appears more likely that the responsible person was Daniel Ekström, who manufactured most of the scientific instruments, including thermnometers, used by both Celsius and Linné.
 
quote:
Originally posted by Tourist:
HI. But where does HTHS comes in? Typically, it's the 10W30 having a higher HTHS figure then 5w30.
Click to expand...
Thats because a "typical" 10/30 will use a higher vis base oil with less VII than compared to a 5/30.
bruce
 
Hi. That's kinda confusing. I thought:

1. Higher HTHS gives better protection, ie. 10W30.

2. Thicker oil at operating temp gives better protection, ie., 5W30.

So which is better as far as protection is concerned?
 
I don't think you can say thicker oil gives better protection....too many other variables. It depends upon engine design, temperature, and load.
 
And this is why people get confused. The first post states that the 0W-30 is thinner than the 10W-30 when cold.

Neither oil is thin when cold but that is what the novice will think. I prefer to say that the 0W-30 has thickened less than the 10W-30 as the oils cooled down. Both are too thick for optimal operation when below 180 F or so.

In general however, there should be less start up wear at any temperature below 180 F for the 0W-30 oil.

aehaas
 
AEHaas, I agree - I was confused exactly as you mentioned. One reason I included a graph was so people wouldn't make this mistake.
Is it working? I hope so!

Back to the HTHS - I'm not qualified to answer. I try to only give answers that I'm confident with. In the mean time, I'll just keep reading like everyone else.
 
There would be less wear from the oil that is less thick below operating temperature. This is because the 0W-30 is less thick than the 10W-30 at all temperatures below operating temperature.

Oil is too thick under the normal operating temperature to function properly. Engines are designed to run a particular oil at operating temperature. Your use of the car then modifies your needs.

If the 30 wt. oil only warmed up so that it had a constant viscosity of 100 cS all the time, then your engine will wear very fast. This is why oil coolers must have a thermostat. The oil must be able to warm up to operating temperature and only get cooling if the oil is too hot.

aehaas
 
So, if there are synthetic Xw-30 oil without VI's, would the oil not benefit from adding a VI to a base oil that would then come out to a -Xw-30, and still protect at higher temps and speeds?
 
quote:
Originally posted by LarryL:
So, if there are synthetic Xw-30 oil without VI's, would the oil not benefit from adding a VI to a base oil that would then come out to a -Xw-30, and still protect at higher temps and speeds?
Click to expand...
A VI improver will only make an oil thicker at hi temps; it won't do anything for the low temp viscosity.

All things being equal, an oil with little or no VI improver is the best option.
 
You missed my comment. I'll restate it, take a thinner oil and ad VI, to make a -0w-30. Now, why would that oil not perform better. Thinner at lower temps should be better in almost any situation. These synthetic oils need little in the way of VI's, if any and thinner when cold would help.
 
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