use shell gasoline with the new nitrogen enriched blah blah 
actually i like that fuel. a lot
actually i like that fuel. a lot
Carbon Build-Up in Piston Rings
- Thread starter fraso
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A correction.
At our club meeting last night, the car with the stuck rings was a 1958 Wolseley and the rings were stuck because the car sat too long. The member used penetrating oil in the cylinders to free up the rings. Likely no motor oil would have prevented this problem but that's how old cars are often found.
It look like modern cars with rings close to the piston top are more likely to suffer stuck rings from carbon build-up than older cars.
At our club meeting last night, the car with the stuck rings was a 1958 Wolseley and the rings were stuck because the car sat too long. The member used penetrating oil in the cylinders to free up the rings. Likely no motor oil would have prevented this problem but that's how old cars are often found.
It look like modern cars with rings close to the piston top are more likely to suffer stuck rings from carbon build-up than older cars.
Originally Posted By: Tom NJ
Believe it or not, all else being equal Group I base oils are less prone to carboneous deposits in high temperature thin film environments than Groups II, III or IV. The higher aromatic content in Group I oils make them more polar and increase solvency, which can reduce deposits by dissolving polymeric oxidation by-products before going to carbon. See this thread from the past:
Re: ISO 100 oil with various basestocks
Not all VI Improvers contribute to deposits - some such as high shear stable dispersant types can be quite clean. I believe the GM ban of 10W-40s was based more on political and marketing concerns than ring sticking.
That's interesting but I looks to me from what you've written is that SA non-detergent mineral oils and POE oils would fare best in the coking test. Besides the higher VI of synthetics (along with their minimal use of VIIs), I thought their other major advantage over conventional oils was high temperature stability. The following web pages would lead someone to believe that synthetics are superior to conventional oils for high temperature conditions:
However, unless I am mistaken, it doesn't look like Group I oils are commonly available either as PCMOs or HDEOs. Of the Groups available, wouldn't coking resistance generally improve with increasing Group number?
Believe it or not, all else being equal Group I base oils are less prone to carboneous deposits in high temperature thin film environments than Groups II, III or IV. The higher aromatic content in Group I oils make them more polar and increase solvency, which can reduce deposits by dissolving polymeric oxidation by-products before going to carbon. See this thread from the past:
Re: ISO 100 oil with various basestocks
Not all VI Improvers contribute to deposits - some such as high shear stable dispersant types can be quite clean. I believe the GM ban of 10W-40s was based more on political and marketing concerns than ring sticking.
That's interesting but I looks to me from what you've written is that SA non-detergent mineral oils and POE oils would fare best in the coking test. Besides the higher VI of synthetics (along with their minimal use of VIIs), I thought their other major advantage over conventional oils was high temperature stability. The following web pages would lead someone to believe that synthetics are superior to conventional oils for high temperature conditions:
- Mobil 1 TV Ep 3: Protecting Critical Turbocharger Parts
- Mobil1 - What makes synthetic oil superior to conventional oil?
- Amsoil Comparative Motor Oil Testing
- Redline Synthetic Oil Advantages
- Schaeffer Oil - Supreme 9000 product description
- Quaker State - Ultimate Durability Synthetic
- Valvoline - Synthetic Oil Benefits
However, unless I am mistaken, it doesn't look like Group I oils are commonly available either as PCMOs or HDEOs. Of the Groups available, wouldn't coking resistance generally improve with increasing Group number?
High temperature stability and coking tendencies are two very different properties. The broad term "high temperature stability" includes oxidative stability (resistance to reaction with oxygen), thermal stability (resistance to degradation by heat), hydrolytic stability (resistance to reaction with water) and coking propensity (tendency to lay down deposits). Most test methods involve various combinations of these conditions and therefore do not all give the same results. A base oil that has excellent thermal and oxidative stability such as PAO can give terrible coking, while a base oil with weaker thermal stability such as diesters can give excellent oxidation and coking results.
The coking test used in the reference link combines thermal stress (540F), oxidative stress (air flow over oil film), hydrolytic stress (water saturated air), volatility (thin film at high temperature), and solvency (oil flowing over residues). Solvency plays a major role in coking and often reverses the correlation of coking to other high temperature properties. A polar oil with good solvency will dissolve or disperse degradation by-products before they can polymerize into insoluble carboneous deposits.
PAOs and many Group IIIs are completely paraffinic and have virtually no polarity to dissolve degradation by-products. While they will breakdown more slowly than a Group I due to their superior thermal and oxidative stability, their solvency is so poor they just can't cope with polymeric degradation by-products and lay them down as deposits. Group I oils breakdown more quickly, but are better at cleaning up their own mess due to their higher polarity.
In a motor oil, all else being equal, higher groups would give longer life and less oil thickening than Group I. In theory they would not be as clean as Group I, but in reality the additives are adjusted to correct this deficiency. But no, they would not give less coking than Group I based oils unless dosed up with esters or high detergent levels.
Tom NJ
The coking test used in the reference link combines thermal stress (540F), oxidative stress (air flow over oil film), hydrolytic stress (water saturated air), volatility (thin film at high temperature), and solvency (oil flowing over residues). Solvency plays a major role in coking and often reverses the correlation of coking to other high temperature properties. A polar oil with good solvency will dissolve or disperse degradation by-products before they can polymerize into insoluble carboneous deposits.
PAOs and many Group IIIs are completely paraffinic and have virtually no polarity to dissolve degradation by-products. While they will breakdown more slowly than a Group I due to their superior thermal and oxidative stability, their solvency is so poor they just can't cope with polymeric degradation by-products and lay them down as deposits. Group I oils breakdown more quickly, but are better at cleaning up their own mess due to their higher polarity.
In a motor oil, all else being equal, higher groups would give longer life and less oil thickening than Group I. In theory they would not be as clean as Group I, but in reality the additives are adjusted to correct this deficiency. But no, they would not give less coking than Group I based oils unless dosed up with esters or high detergent levels.
Tom NJ
Originally Posted By: Tom NJ
The coking test used in the reference link combines thermal stress (540F), oxidative stress (air flow over oil film), hydrolytic stress (water saturated air), volatility (thin film at high temperature), and solvency (oil flowing over residues). Solvency plays a major role in coking and often reverses the correlation of coking to other high temperature properties. A polar oil with good solvency will dissolve or disperse degradation by-products before they can polymerize into insoluble carboneous deposits.
The coking test at 540°F seems to be relevant for upper ring carbon formation. The Redline Motor Oil Information Sheet suggests that the upper ring area can see temperatures in the range of 600°F.
Originally Posted By: Tom NJ
In a motor oil, all else being equal, higher groups would give longer life and less oil thickening than Group I. In theory they would not be as clean as Group I, but in reality the additives are adjusted to correct this deficiency. But no, they would not give less coking than Group I based oils unless dosed up with esters or high detergent levels.
Aren't PAO oils normally dosed up with POE esters for seal conditioning anyway?
Would a PAO-based CJ-4 HDEO have the esters and detergents that would provide the coking resistance of a Group I oil?
The coking test used in the reference link combines thermal stress (540F), oxidative stress (air flow over oil film), hydrolytic stress (water saturated air), volatility (thin film at high temperature), and solvency (oil flowing over residues). Solvency plays a major role in coking and often reverses the correlation of coking to other high temperature properties. A polar oil with good solvency will dissolve or disperse degradation by-products before they can polymerize into insoluble carboneous deposits.
The coking test at 540°F seems to be relevant for upper ring carbon formation. The Redline Motor Oil Information Sheet suggests that the upper ring area can see temperatures in the range of 600°F.
Originally Posted By: Tom NJ
In a motor oil, all else being equal, higher groups would give longer life and less oil thickening than Group I. In theory they would not be as clean as Group I, but in reality the additives are adjusted to correct this deficiency. But no, they would not give less coking than Group I based oils unless dosed up with esters or high detergent levels.
Aren't PAO oils normally dosed up with POE esters for seal conditioning anyway?
Would a PAO-based CJ-4 HDEO have the esters and detergents that would provide the coking resistance of a Group I oil?
Originally Posted By: fraso
Aren't PAO oils normally dosed up with POE esters for seal conditioning anyway?
Would a PAO-based CJ-4 HDEO have the esters and detergents that would provide the coking resistance of a Group I oil?
Not necessarily. Seal conditioning requires a lot less polarity than what would be needed to effectively affect coking. And there are seal swell additives more potent than POEs. Oils intended for HD diesel engines are usually designed for lower ring deposits since the problem is more prevalent in these engines.
Tom NJ
Aren't PAO oils normally dosed up with POE esters for seal conditioning anyway?
Would a PAO-based CJ-4 HDEO have the esters and detergents that would provide the coking resistance of a Group I oil?
Not necessarily. Seal conditioning requires a lot less polarity than what would be needed to effectively affect coking. And there are seal swell additives more potent than POEs. Oils intended for HD diesel engines are usually designed for lower ring deposits since the problem is more prevalent in these engines.
Tom NJ
Yes, VII's are particularly suspect in piston ring sticking issues. John--Las Vegas.
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