Oil 101 - Revised and Expanded Chapter 3

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Originally Posted By: Solarent
I think it is time to update Motor Oil 101. It gets quoted a lot and has helped many people begin to understand some of the basics. Without getting too technical I’ve followed the same general format, but re-written the topics so it is more accurate.
No disrespect to AE Haas, his article has helped many and will continue to do so.
I welcome your comments and input and hopefully if this ends up replacing the current Motor Oil University, the powers that be at BITOG will also take them into consideration.


Chapter 3 Viscosity Modifiers and Engine Oil

In chapter 1 we talked about how in the early days of the automobile, engine oils were very simple, basic refined fluids that helped keep moving parts easily sliding past each other. As time has passed, engines and engine oil has become more complex – allowing for different grades of oil with similar high temperature performance, but one being much close to the correct viscosity at startup. This is achieved using additive chemicals called viscosity modifiers.

Now I’m not going to go into a huge description of all the different types, shapes and styles of chemicals used to modify the viscosity, or into a long discussion about how they work. But what we can say is that oil makers use these molecules to change the way that the final oil blend responds to changes in temperature. This makes it possible to have 0W30, 5W30, 10W30 and so on.

Today’s engine oil is made up of several important components – the base oil mix, the viscosity modifying additives and other additives that have functions like preventing wear, cleaning an engine, making oil drain intervals longer etc. Right now we will focus on base oils and viscosity modifiers.

To get the right viscosity at operating temperature (in our example this is a 10cSt oil at 212F or a XW30 oil) the oil maker will select a mix of base oils and a viscosity modifier (also sometimes called a Viscosity Index Improver –VII) to make it so the final blend hits that window. This may be a mixture of 6cSt and 8cSt base oil with a VII that puts the final blend into the XW30 grade. It could also be a mixture of 4cSt and 6cSt base oil with more VII that puts the final blend into the XW30 grade. The ratios of base oil and VII all impact the viscosity of the final blend. There are lot of reasons why an oil maker would choose a different mixture. Sometimes it is for better low temperature performance, sometimes it is due to cost or other manufacturing logistics. The trick is balancing the needed cold temperature performance while still hitting the XW30 grade target.

One of the downsides of using thinner base oils and VII’s to get to the high temperature performance window is that some VII’s wear out over time. In fact some oils do thin out over time. This may be some of the reason for Porsche (according to some people) do not want to use a 0W30 but would rather a 10W30. The thinking here is that if the VII wears out then the oil might fall out of the XW30 window and instead become an XW20 oil which would be too thin based on the engine manufacturer’s recommendation. This isn’t really what happens in real life. While some VII’s do lose some of their effectiveness over time, in a normal engine, running under everyday conditions most are very robust and will keep your engine oil in grade – in fact this is a requirement for a lot of engine oil specifications that the oil stays “in grade” over the life of an oil change interval.

There is also another class of viscosity modifiers called Pour Point Depressants (PPDs). PPDs function by getting in the way of forming wax crystals as the temperature gets cooler. Mineral based oils naturally start to form wax crystals and this can change how much the oil thickens when it starts to get cold. This is another way where the oil maker can influence the cold temperature performance (the XW part) without greatly changing the high temperature performance of the final oil formula.

Sometimes oil will thin out, but this is partly from fuel dilution and could also be partly by VII’s wearing out. What is more interesting is that with further use, the engine oil actually starts to thicken and this is much worse than the minimal thinning that would happen before. This thickening is usually caused as the oil oxidizes and can start to form varnish and sludge on engine parts. Changing your engine oil before it gets too oxidized can help keep engine parts clean and is one of the main factors that engine makers consider when recommending how often oil should be changed.

Generally engine manufacturers are now recommending lighter engine oils in both parts of the grade (ie choosing 0W20 over 5W30). One of the main reasons for this is because remember both oils are still going to be much thicker than the target operational viscosity at start-up, so if they can start out thinner, it will reach the operational viscosity window faster and by consuming less energy. This translates into better fuel economy. Engine oils will continue to be optimized lower and lower with engines designed to run on a 6 cSt oil instead of a 10 cSt oil at operating temperature in order to save fuel. This is a good thing for everyone – although these oils often require more complex formulas and better quality base oils. This is where synthetic oils come in.
 
Good stuff Sol, keep it up.
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IN
Quote:
Sometimes oil will thin out, but this is partly from fuel dilution and could also be partly by VII’s wearing out. What is more interesting is that with further use, the engine oil actually starts to thicken and this is much worse than the minimal thinning that would happen before. This thickening is usually caused as the oil oxidizes and can start to form varnish and sludge on engine parts. Changing your engine oil before it gets too oxidized can help keep engine parts clean and is one of the main factors that engine makers consider when recommending how often oil should be changed...


you could potentially discuss volatility as one of the causes as well.
 
Originally Posted By: MolaKule
Good stuff Sol, keep it up.
thumbsup2.gif


IN
Quote:
Sometimes oil will thin out, but this is partly from fuel dilution and could also be partly by VII’s wearing out. What is more interesting is that with further use, the engine oil actually starts to thicken and this is much worse than the minimal thinning that would happen before. This thickening is usually caused as the oil oxidizes and can start to form varnish and sludge on engine parts. Changing your engine oil before it gets too oxidized can help keep engine parts clean and is one of the main factors that engine makers consider when recommending how often oil should be changed...


you could potentially discuss volatility as one of the causes as well.


Agreed - we don't want to make it too technical though - perhaps you could take a stab at revising that paragraph to include something about volatility?
 
It's a technical subject though. We don't need to introduce stribeck curves and the like, but what we say should be factual if a bit vague.
 
Partially re-written. Please read and see if closer to the mark ...

Originally Posted By: Solarent

One of the downsides of using thinner base oils and VII’s to get to the high temperature performance window is that some VII’s wear out over time. In fact some oils do thin out over time. This may be some of the reason for Porsche (according to some people) do not want to use a 0W30 but would rather a 10W30 or a 15W-50. For this manufacturer, please read the latest edition of the Porsche A-40 approved oils list.

The thinking here is that if the VII wears out then the oil might fall out of the XW30 window and instead become an XW20 oil which would be too thin based on the engine manufacturer’s required film strength and depth within the bearing clearances as manufactured. Porsche's are often bought to run hard and fast. At high RPM internal oil friction in the journal and shearing in the bearings means the oil is even thinner, so the need to be especially careful with the "window" of acceptable viscosities.

This isn’t really what happens in real life to most motors. While some VII’s do lose some of their effectiveness over time, in a normal engine, running under everyday conditions most oils are very robust and will maintain reasonable viscosity and stay in grade. In fact this is a requirement for a lot of engine oil specifications that the oil stays “in grade” over the life of an oil change interval.

There is also another class of viscosity modifiers called Pour Point Depressants (PPDs). PPDs function by getting in the way of forming wax crystals as the temperature gets colder. Remember we talked about oils becoming gelled and separating when they get too cold... Mineral oils naturally start to form wax crystals at reduced temperatures. And this can change how much the oil thickens when it starts to get too cold. This is another way where the oil maker can influence the cold temperature performance (the XW part) without greatly changing the high temperature performance of the final oil formula. PPD's push this gelling and separation to lower temperatures, so the oil stay liquid longer.

Sometimes oil will thin out, this may be partly from fuel dilution and could also be partly because VII’s wear out (shear). What is interesting is that with further use, the engine oil actually starts to thicken and this is much worse than the minimal thinning that might happen before.

This thickening is usually caused as the oil oxidizes and can start to form varnish and sludge on engine parts. Changing your engine oil before it gets too oxidized can help keep engine parts clean and is one of the main factors that engine makers consider when recommending how often oil should be changed.

Generally engine manufacturers are now recommending lighter engine oils in both parts of the grade (ie choosing 0W20 over say a 5W30). One of the main reasons for this is because remember both oils are still going to be much thicker than the target operational viscosity at start-up, so if they can start out thinner, it will reduce the parasitic drag caused by cold oil and consume less energy while warming up. This translates into better fuel economy.

Engine oils will continue to be optimized lower and lower with engines designed to run on a 6 cSt oil instead of a 10 cSt oil at operating temperature in order to save fuel. This is a good thing for everyone – although these oils often require more complex formulas and better quality base stocks. This is where synthetic oils come in.
 
Paragraph 7 addition:

Quote:
Sometimes oil will thin out, but this is partly from fuel dilution and could also be partly by VII’s wearing out. What is more interesting is that with further use, the engine oil actually starts to thicken and this is much worse than the minimal thinning that would happen before. This thickening is usually caused as the oil oxidizes and can start to form varnish and sludge on engine parts. Changing your engine oil before it gets too oxidized can help keep engine parts clean and is one of the main factors that engine makers consider when recommending how often oil should be changed.

Thickening of the oil (an increase in viscosity) can also result from the lighter fractions of the oil "evaporating" or "volatizing" at high temperatures. Most base oils are mixtures of both low viscosity and higher viscosity oils. It is the lower viscosity oils that have a tendency to evaporate and leave behind the higher viscosity oils with oxidation by-products, thus causing thickening of the engine oil over time. Synthetic base oils have a lower tendency to volatize because of their inherent viscosity index.


Good work Solarent
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Disagree with a little of this well written paragraph. The quote: "Synthetic base oils have a lower tendency to volatize because of their inherent viscosity index." I consider to be incorrect. Some synthetic base oils have lower tendency to volatize because they have fewer volatile molecules. The volatility range of a PAO synthetic depends on it's viscosity. A light PAO say PAO 3 will evaporate at a much higher rate than an 600N Group I or II in an automobile engine at normal operating temperature. Also since there are so many different synthetics out there, I usually assume you mean Grp IV when you are talking about the benefits of synthetics.
 
Originally Posted By: DWC28
Disagree with a little of this well written paragraph. The quote: "Synthetic base oils have a lower tendency to volatize because of their inherent viscosity index." I consider to be incorrect. Some synthetic base oils have lower tendency to volatize because they have fewer volatile molecules. The volatility range of a PAO synthetic depends on it's viscosity. A light PAO say PAO 3 will evaporate at a much higher rate than an 600N Group I or II in an automobile engine at normal operating temperature. Also since there are so many different synthetics out there, I usually assume you mean Grp IV when you are talking about the benefits of synthetics.


Synthetic oils have greater inherent VI and lower volatility because of their molecular structure.

What I would be comparing is the volatility of a 64742-XX-X designated mineral oil of 100N (4.0 cSt@100C) with a 4.0 cSt PAO or Ester.

I would not compare a 3.0 cSt PAO with a 11.9 cSt Group II 600N mineral oil.
 
Originally Posted By: MolaKule
What I would be comparing is the volatility of a 64742-XX-X designated mineral oil of 100N (4.0 cSt@100C) with a 4.0 cSt PAO or Ester.

I would not compare a 3.0 cSt PAO with a 11.9 cSt Group II 600N mineral oil.


You are correct, but on a different point than I was trying to make. Light oils say a 0W-8 is generally more volatile than a heavier oil say a 10W-30, regardless of base oil used. If you wanted to do a very narrow cut mineral oil you could come close to a PAO or GTL. I agree mineral oils are wide cut which results in both higher and lower boiling points than narrow cuts.
 
great info as always, read more + learn more! remember amsoil stating some time ago their PAO 30 meets the 10-30 spec without VII's. also wondering what most mineral base oils are used to create various mixes as i also remember seeing that the narrower spreads were better, + a 20-50 was not as "fragile" as a 10-40 even though theres the same 30 spread because a 10-40 starts as a 10W + the 20-50 starts as a 20W. information should identify what group of base oil is being compared as many uninformed readers do not know about group III refined crudes compared to synthesised group IV PAO + V Ester oils. the more i read + learn the more i realize how complicated oil blends can be!!!!
 
The main target here is the education of the daily driver or newbie (not the diesel, aviation, or marine engineer) and giving him/her the information to make an educated decision.

There have been many discussions on formulations of engine oils in specific threads but MOU 101 is not the place to discuss specifics, IMHO.


[quote-Solarent]Pick a brand you are comfortable with and start to learn about the different specifications and applications oils are designed for.[/quote]

I think that is the main message.
 
a different challenge for sure but oil "discussions" on motorcycle forums show how little many know. surely a hot running large V-Twin like my 106 Vic Hammer with a shared oil supply is quite hard on typical mineral oils
 
Originally Posted By: benjy
a different challenge for sure but oil "discussions" on motorcycle forums show how little many know. surely a hot running large V-Twin like my 106 Vic Hammer with a shared oil supply is quite hard on typical mineral oils
It is hard on syn oils as well.
 
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