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Author
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Topic: What do the weights refer to with oil?
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Toronado3800
Gearhead Posts: 364
From: St. Louis, MO
Registered: Jul 2001
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posted 02-07-2003 09:42 PM
  
Another post brought up this question. I understand HD30 is lawnmower oil for summertime and 5w30 is popular for new cars with finley machined engines. 10w40 for warm weather and older motors, and 10w30 for general purpose, but what do the numbers refer to?I've even seen a syntec bottle which said "0w" something. Now that's its got my attention I just need to know. Kinda like calculating how tall my tires are with the nubmers instead of just using a tape measure or knowing higher octane reduces ping by raising resistance to combustion.
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cobravenom71
Gearhead Posts: 808
From: Kissimee, Fl USA
Registered: Aug 2002
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posted 02-07-2003 10:01 PM
The 'weight' of the oil measured with a term called 'viscosity'.
Viscosity is defined as 'Resistance to Flow'.
Oils that are thin and flow easily are considered to be of a low viscosity(like a 5 or 10 weight oil), and oils that are thicker and more resistant to flow are said to have a high viscosity. (like 40 or 50 weight).
The higher the viscosity of an oil, the more tenaciously it wil cling to a surface.
Although motor oil protects your engine from a lot of contaminants through the use of very special and specific additives, it is the viscosity of the oil itself that lubricates the engine.
The viscosity of the oil allows it to provide a 'Hydro-Static Boundry Layer' of oil protection, while the oil pump pressurizes the oil system which 'pushes' the oil in between moving parts and provides a 'Hydro-Dynamic Boundry Layer' of protection.
A multi-grade or multi-viscosity oil has the properties of two differnt viscosities of oil. For example: at lower engine temperatures a 10w-30 motor oil has the viscosity of a lighter, 10-weight oil so it can be easily pumped to the moving parts of the engine, yet as the temperature of the engine increases, a 10-weight oil would thin-out and be far less viscous than acceptable to provide adequate protection. Additives called 'Long Chain Polymers' that are temperature-reactive chemically modify the structure of the oil at higher engine temperatures so as to offer the protection of a 30-weight oil, which is needed at higher operating temps. Pretty cool stuff.
By the way, contrary to popular belief, the 'W' in a multi-viscosity oil(such as 10W-30)stands for 'Winter', not 'Weight'. It simply means that the SAE has classified the oil as adequate to offer engine protection in winter driving conditions. Hope that clears it up a little.
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mtucker
Journeyman Posts: 93
From: Wichita, KS
Registered: Oct 2002
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posted 02-08-2003 09:28 AM
Wow! Great explanation. Gotta say though, "long chain polymers" sounds like a fancy name for "plastic". Those polymers must get sheared at some point and the additive package surely gets gets used up. So how do extended drain interval oils like Amsoil work?
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rdw40
Journeyman Posts: 44
From: Hockessin, DE USA
Registered: Dec 2002
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posted 02-08-2003 09:44 AM
In an oil like a 10W-30, the 10W viscosity is actually measured at 0 F and the 30 is measured at 210 F. The SAE (Society of Automotive Engineers) select a viscosity range that the oil must fall into at each temperature to meet the requirements of different weights.
Synthetic oils may need no polymer or very little polymer compared to petroleum oils. Additionally, synthetics have more uniformly shaped molecules to start with, so they are inherently better for their specific purpose. That is one reason that the synthetics don'e require as many additives.
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Toronado3800
Gearhead Posts: 364
From: St. Louis, MO
Registered: Jul 2001
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posted 02-08-2003 02:00 PM
Thanks for the explanation. It's just nice to understand the numbers and things I deal with everyday.
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cobravenom71
Gearhead Posts: 808
From: Kissimee, Fl USA
Registered: Aug 2002
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posted 02-08-2003 02:42 PM
'Long Chain Polymers' are one of the additives that help a multi-grade oil to work effectively in two seperate viscosity ranges.
A simple explanation is that they are 'coils' that are wound tightly, and they have little 'barbs' on them that lay nice and flat.When cold, they 'mind thier own business', and they don't interact with each other.
However, when they heat up they uncoil and the barbs stick out. These now-straight polymers start to 'link-up' with each other creating 'long chains.' This creates a fibrous condition that gives the oil the properties of a higher viscosity oil.
As mentioned earlier, the shearing action of the engine does indeed tear these additives apart, and after some time they can no longer be effective.
The wider the viscosity range, the more 'LCP' additives it takes to achieve the rating. This higher level of additives means that they can be 'sheared' quicker, therefore it is not as 'durable'.
10W-30 is far more durable than 10W-40, due to less 'LCP' additives.(this only applies to conventional 'dino' oil, not synthetics.)
An interesting fact is that the ratio of additives to base-stocks(oil) is always a compromise. Most 'dino' oils are around 15-20% additives. More additives in the formula may give some extra protection, but it leaves less room for actual 'oil', which is required for lubrication and cooling.
Synthetic motor oil does such an outstanding job that it needs fewer additives to 'modify' its performance. Fewer additives mean that it is more resistant to the shearing action of the engine, giving it a little longer usable life than regular 'dino'.
Synthetics have around 5-15% additives leaving more room for actual 'oil'. This is why Synthetic oil gives better gas mileage and the car runs cooler.
Amsoil claims the extra-long intervals due to the fact they put more additives in the oil so it can withstand more shearing action. Some grades of Amsoil have about 33% additives, which leaves less room for the actual oil. To me, that is not a fair trade-off.
I use Mobil 1 Synthetic, and it is about the best, easily availible oil there is.
However, the highest-rated oil in all aspects currently is 'Scheaffers'. However, it is expensive and difficult to find to find in some locations.
Surprisingly, if you are using regular 'Dino' oil, one of the best rated currently availible oils availible is (are you ready?)...'Super-Tech', the Wal-Mart house brand oil. It is Penzoil, and it is about $4.00 for a 5-quart jug.
The 'Super-Tech' oil filters are also very good, and only $1.97 each! They ahve one of the highest ratings in both the single-pass and multi-pass efficiency test. These are rated at a 5-micron level.(about half the thickness of a human hair). These filters use a synthetic-blend filter media, and are constructed well. Incidentally, 'Fram' filters are now one of the worst-rated filters on the market. They drastically lowered thier quality to be able to meet the bid for Wal-Mart.( a HUGE contract).
Hope this explains a little.
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rdw40
Journeyman Posts: 44
From: Hockessin, DE USA
Registered: Dec 2002
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posted 02-08-2003 11:49 PM
I thought a human hair was about 2 micron?
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cobravenom71
Gearhead Posts: 808
From: Kissimee, Fl USA
Registered: Aug 2002
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posted 02-09-2003 08:55 AM
The human-hair analogy is a little vague. A human hair can be anywhere from about 2 to over 10 microns, but it is used a lot as a descriptor to help give the subject some 'scale'.
Oil filters are tested using two different tests: The first-pass test and the multi-pass test.
A specific amount of particulate matter is put into some technical-grade oil(unavailible to consumers) and the entire amount of oil is passed through the filter one time. The amount of matter collected is given a first-pass rating.
This tells how well a filter is at trapping matter, but it doesn't give any indication as to how soon it may 'clog-up' and go into by-pass.
The same test is performed for the multi-pass test, except the oil is continually passed through the filter in a loop for a specific amount of time and the matter collected is measured again.
This test gives some indication as to how well a filter will continue to filter a continuos flow without going into by-pass, which would translate to unfiltered oil being pumped through an engine.
Some filters perform so poorly when cold, that they completely by-pass until the oil has reached a higher temperature.
This is more common on filters that use an organic, hardwood-based(paper) filter media.
Filters that use a synthetic media, like the 'M1'(Mobil 1) and 'Pure-1' (Purolater)use synthetic media that is far superior at cold temperatures.
The oil filter companys can report thier specs as they see fit, to some degree.Some report thier findings measured at a 10-micron level to increase the reported percentage, while others report thiers at a more realistic 5-micron level.
There are some engineers that claim that anything smaller than 3-microns has no effect on the internals of an engine, but I don't agree with this.
Oil filters are tested by thier manufacturers and thier figures are taken as factual. It's kind of an honor system, as they don't have to be 'approved' through actual testing by any governing body.
Strangely, the motor oil viscosity ratings are done the same way.
The only way to be absolutely sure about the actual performance of any filter or oil is to have it tested by an independent lab, which is done all the time.
That is why some well-known names don't always test as well as you would think, and some lesser-known names are getting some very impressive results.
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