Ok, now before you get too excited and roll out the troll icon, let me qualify a bit. I'm talking about VARNISH potential only.
A while back there was a post which said Castrol Syntec was removing top end varnish. This drew my skeptical response among some others as a group IV oil had been previously used. See this thread:
http://theoildrop.server101.com/forums/s...part=1&vc=1
More recently I've become aware of a varnish problem we are having with one of the turbines in our fleet, and have done a bit more research into it, with some very interesting findings:
1. This is a fairly recent problem in the industry and by some accounts reaching "epidemic" proportions. The prime cause is very surprising - better quality base oils. Turbine oils have switched from Group I to Group II over the past 10-15 years or so, and problems are now showing up that have not been seen before. More on that later.
2. The other issue is that additives for these newer more advanced base oils have to be carefully selected or they can result in severe varnish problems.
Other more minor findings are that varnish tends to form on cooler surfaces because solubility of varnish in oil reduces with temperature (contrary to what I thought). Appliations where there is start-up and cool down cycles are more susceptible to varnish (like autos).
The basic problem with the base oils was one I raised in the Group III vs IV discussion and that of reduced solubility of the higher group oils. Not only is it harder to dissolve additives, it is also harder to keep sludge such as varnish in suspension, with this reduced solvency.
One specification for base oils that is not so common but important is the aniline point. It is a measue of the solvency of the oil, with a lower number meaning higher solvency. See this graphic for a comparison of the aniline number by base oil group. The second table is irrelevant for this discussion.
As you can see that Group I is the best. This stands to reason as one of the distinguishing charateristics of the higher base oils is lower aromatic content, and resulting higher flash point. These aromatics however are probably responsible for the higher solubility of the oil.
So long story, but I can now understand and believe that switching from a Group IV synthetic to a lower base oil group or one with better additives can dissolve varnish as was reported in the thread above. There are a number of cases of this happening when methods are implemented to remove varnish from turbine oils. Under the right conditions varnish can be redissolved. I'm not so sure however, that other than cosmetic coloring, varnish is a real big problem in auto engines? Perhaps it may plug oil filters sooner especially fine ones, or constrict small oil flow orifices, especially ones in cooler areas of the engine.
So two questions, with the second one being somewhat off topic:
1. Should we periodically go out and find a group I based oil and keep it in for an oil change to clean out the varnish we may be accumulating by using the "high quality" synthetic oils? If so, what group I oil may be the best quality, given the other problems with group I? Doing this in summer would seem to be one of the obvious safeguards.
2. This one is
If you had a turbine with severe varnish problems how would you select a good replacement oil? Will manufacturers actually tell you what base oil they use? Or do you just pick one with the lowest possible viscosity index? Are there specific additives that are good and bad with respect to varnish in Group I or II? Bruce, I think you and others may have experience here.
There are many articles on the net re varnish in turbine oils if you look. Here is one.
http://www.practicingoilanalysis.com/article_detail.asp?articleid=428&relatedbookgroup=PowerGen
A while back there was a post which said Castrol Syntec was removing top end varnish. This drew my skeptical response among some others as a group IV oil had been previously used. See this thread:
http://theoildrop.server101.com/forums/s...part=1&vc=1
More recently I've become aware of a varnish problem we are having with one of the turbines in our fleet, and have done a bit more research into it, with some very interesting findings:
1. This is a fairly recent problem in the industry and by some accounts reaching "epidemic" proportions. The prime cause is very surprising - better quality base oils. Turbine oils have switched from Group I to Group II over the past 10-15 years or so, and problems are now showing up that have not been seen before. More on that later.
2. The other issue is that additives for these newer more advanced base oils have to be carefully selected or they can result in severe varnish problems.
Other more minor findings are that varnish tends to form on cooler surfaces because solubility of varnish in oil reduces with temperature (contrary to what I thought). Appliations where there is start-up and cool down cycles are more susceptible to varnish (like autos).
The basic problem with the base oils was one I raised in the Group III vs IV discussion and that of reduced solubility of the higher group oils. Not only is it harder to dissolve additives, it is also harder to keep sludge such as varnish in suspension, with this reduced solvency.
One specification for base oils that is not so common but important is the aniline point. It is a measue of the solvency of the oil, with a lower number meaning higher solvency. See this graphic for a comparison of the aniline number by base oil group. The second table is irrelevant for this discussion.
As you can see that Group I is the best. This stands to reason as one of the distinguishing charateristics of the higher base oils is lower aromatic content, and resulting higher flash point. These aromatics however are probably responsible for the higher solubility of the oil.
So long story, but I can now understand and believe that switching from a Group IV synthetic to a lower base oil group or one with better additives can dissolve varnish as was reported in the thread above. There are a number of cases of this happening when methods are implemented to remove varnish from turbine oils. Under the right conditions varnish can be redissolved. I'm not so sure however, that other than cosmetic coloring, varnish is a real big problem in auto engines? Perhaps it may plug oil filters sooner especially fine ones, or constrict small oil flow orifices, especially ones in cooler areas of the engine.
So two questions, with the second one being somewhat off topic:
1. Should we periodically go out and find a group I based oil and keep it in for an oil change to clean out the varnish we may be accumulating by using the "high quality" synthetic oils? If so, what group I oil may be the best quality, given the other problems with group I? Doing this in summer would seem to be one of the obvious safeguards.
2. This one is
There are many articles on the net re varnish in turbine oils if you look. Here is one.
http://www.practicingoilanalysis.com/article_detail.asp?articleid=428&relatedbookgroup=PowerGen
