Redline (and other) Polyolester Oils and Moisture

[engineerscott]

So, Redline and a few other synthetic oils (Motul being a second one that I can name off the top of my head) are generally recognized to be mostly (or perhaps exclusively) composed of polyolesters. Because polyolesters are products of the esterification of a organic acid, this process can be reversed in the presence of water and heat.

Apparently the people using POEs in the AC compressor industry have had some issues with this occurring in refrigeration systems. I would have thought that the desiccant in the dryer would take care of this, but perhaps at some point it becomes saturated and stops sequestering water in the system.

So, my question is to what extent should I be concerned about this in my consideration of switching to Redline or Motul? Obviously people are using Redline and Motul with great success, but I'm worried that my particular application might be more prone to problems. I am wanting to use one of these oils (leaning towards Redline) in a car that I have restored. What bothers me is that the car will be garaged about half the year, and when not garaged will probably be driven mostly on the weekends with the occasional weekday trip when the mood strikes. Does having a car sit idle for protracted periods make the moisture/POE issue more of a problem?

If I understand the chemistry correctly, both water and heat are required to reverse the esterification process to yield organic acids. Is this correct? If so, I would think that POEs would not tend to revert to organic acid even when moisture was present if it is at relatively low temperature (or say, any temperature below 90*F). Is this right?

Also, I think I've heard that POE motor oil makers actually blend different POEs and perhaps even diesters to help reduce the issue of reverse esterification. Anyone know anything about this?

So, if any of you chemical/tribology gurus can comment on this I would greatly appreciate it.

Thanks,

-Scott

 

[Boomer]

This reaction is greatly accelerated by the presence of acid so a good TBN works in your favor on this. Personally, I would hesitate to use an ester oil on a vehicle that was only driven on short trips and not thoroughly warmed up. If I was driving longer distances, no hesitation whatsoever.

 

[JHZR2]

+1. Best practice, IMO (and I do this personally) is that when the seldom-used vehicles are operated, AC is running and the car is brought up to full oil temp.

 

[Lethal1ty17]

there was a UOA on here about a week or so ago about someone who had changed the oil in either a motorcycle or a car 17 years ago with castrol gtx and just let it sit. the UOA surprisingly came back pretty good and blackstones comment was something to the degree of "if you hadnt mentioned the age we would have never known it, looks like sitting in a sump for a long time has little detrimental effects on the oils additives"

 

[saaber1]

This has been discussed and debunked numerous times on this site. It's not an issue in motor oils.

Originally Posted By: Tom NJ
The esters used for refrigeration applications are dried to a water content of
Tom NJ


Originally Posted By: Tom NJ
Hydroscopicity, a liquid's capacity to absorb and solubilize water, is different than hydrolytic stability, a liquid's capacity to react with water.

Esters are not considered very hydrolytically stable, but they vary according to structure, and the conditions needed to break them are pretty severe. The net effect in motor oils is not significant - you may see a rise in TAN but not the corrosive type.

Polyol esters are more hydrolytically stable than diesters, which were used for many years in synthetic motor oils without problems. Advanced POEs are quite hydrolytically stable. Nearly 40 years of ester use in motor oils have not demonstrated any performance issues with respect to their hydrolytically stability.

Tom NJ

 

[dparm]

Would this sort of thing show up in a UOA?

 

[ItsuMitsubishi]

Originally Posted By: saaber1
This has been discussed and debunked numerous times on this site. It's not an issue in motor oils.

Originally Posted By: Tom NJ
The esters used for refrigeration applications are dried to a water content of
Tom NJ


Originally Posted By: Tom NJ
Hydroscopicity, a liquid's capacity to absorb and solubilize water, is different than hydrolytic stability, a liquid's capacity to react with water.

Esters are not considered very hydrolytically stable, but they vary according to structure, and the conditions needed to break them are pretty severe. The net effect in motor oils is not significant - you may see a rise in TAN but not the corrosive type.

Polyol esters are more hydrolytically stable than diesters, which were used for many years in synthetic motor oils without problems. Advanced POEs are quite hydrolytically stable. Nearly 40 years of ester use in motor oils have not demonstrated any performance issues with respect to their hydrolytically stability.

Tom NJ


Thanks for pulling these up! Definitely puts things in perspective.

Originally Posted By: lnengineering.com
Most of these ZDDP concentrates omit detergents altogether or use over-based Ca detergents known to reduce the efficiency of the anti-wear properties of the oil! Just like you need more Zn and P in an oil that has more detergents, you also have to have additional detergency because of the breakdown of ZDDP in peroxides and its interaction with combustion byproducts to form sulfuric acid.


IIRC, any acids formed by reactios with esters are very weak and may even raise TAN technically, but certainly not a concern as sulfuric acid formation by the breakdown of the oil's own AW additives.

 

[engineerscott]

Originally Posted By: saaber1
This has been discussed and debunked numerous times on this site. It's not an issue in motor oils.

Originally Posted By: Tom NJ
The esters used for refrigeration applications are dried to a water content of
Tom NJ


Originally Posted By: Tom NJ
Hydroscopicity, a liquid's capacity to absorb and solubilize water, is different than hydrolytic stability, a liquid's capacity to react with water.

Esters are not considered very hydrolytically stable, but they vary according to structure, and the conditions needed to break them are pretty severe. The net effect in motor oils is not significant - you may see a rise in TAN but not the corrosive type.

Polyol esters are more hydrolytically stable than diesters, which were used for many years in synthetic motor oils without problems. Advanced POEs are quite hydrolytically stable. Nearly 40 years of ester use in motor oils have not demonstrated any performance issues with respect to their hydrolytically stability.

Tom NJ


Thanks, this is just the type of technical discussion I was looking for.

Someone else commented about the relative strength of the organic acids that evolve due to reverse esterification. They are indeed week acids, nothing like having HCL or H2SO4 in your crankcase.

I supposed that the concern over acids forming as a result of the breakdown of POEs probably did spill over from refrigeration, where there are greater problems with material compatibility with even mildly acidic conditions. There certainly are lots of white papers on the problems of moisture and POE based lubrication in refrigeration systems and relatively few about this issue with respect to automotive lubrication (that should have been a big clue I suppose that this is not recognized to be an problem).

BTW, sorry I didn't find the prior discussions of this. I did look but sometimes the keywords I search for don't end up being the keywords the rest of the world might use.

Thanks,

-Scott

 

[saaber1]

No problem Scott. If you search for posts by Tom NJ, you'll find a wealth of info. on esters. Molakule has some excellent ones as well. Those 2 guys are about as knowledgeable as they come when it comes to esters. GlennC (sp?)and Barkerman have some great old posts regarding real world use of ester oils. Also there are some pre-2007 posts from Terry Dyson (username "Terry") that are very helpful.

 

[Bruce T]

The old threads can be tricky to find, but saaber1 is quoting Tom NJ, who is probably the best resource available on esters. I don't know enough to discuss the chemistry side, but here is another quote and some related threads:

"Another potential disadvantage with esters is their ability to react with water or hydrolyze under certain conditions. Generally this hydrolysis reaction requires the presence of water and heat with a relatively strong acid or base to catalyze the reaction. Since esters are usually used in very high temperature applications, high amounts of water are usually not present and hydrolysis is rarely a problem in actual use. Where the application environment may lead to hydrolysis, the ester structure can be altered to greatly improve its hydrolytic stability and additives can be selected to minimize any effects."

Taken from "An Overview of Esters in Synthetic Lubricants":

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1252272&page=all

"All that acid in RLI oil (Renewable Lubricants)":

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1486512&page=all

"TBN and TAN in ester oils":

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1583684&page=all

 

[Ben99GT]

Originally Posted By: Molakule
Esters do not have an "affinity" for water, nor are they anymore micible with water than mineral oils or PAO's.

IF the crankcase oil became very acidic, have a lot of moisture in it, AND the oil became very hot (about 400 F), you might "hydrolize" the ester and break it apart.

However, by the time the oil temp got over 220 F the moisture would be driven off.

But that is why you have other additives to control acidity. If for some reason the TAN rose to a high level by some quirk, you are going to be worrying less about hydrolisis of esters and be worrying more about corrosion.

 

[ItsuMitsubishi]

Ah! So it's hydrolysis that's responsible for the breakdown of the ester. Was racking my brain trying to figure out the correct terminology. I finally know what to search for now to learn more about this. Thanks Ben for pulling that up

 

[Ben99GT]

Originally Posted By: Dave @ Red Line
Thank you for contacting Red Line Oil, our oils are designed and suitable for extended drain intervals, once past warranty we recommend a drain interval of 10 to 18,000 miles or at least once a year. The lower molecular weight esters tend to be hydroscopic, our oils use higher molecular weight stocks that don't exhibit that tendency. At operating temperatures moisture from combustion is released as the case with other stocks.

Regards, Dave
Red Line Oil


Originally Posted By: Tom NJ
Redline's reply is correct. Hydroscopic refers to a liquid's capacity to absorb and solubilize water. Higher molecular weight esters will only solubilize 0.1 to 0.2% water, and even this will be released under vacuum and heat.

Tom NJ

 

[Tom NJ]

Others have already quoted my view on hydrolysis here. The problem in refrigeration systems was the clogging of capillary columns by metal carboxylates, which were believed to be formed from the acids liberated from POEs. Later it was found that residual compounds from metal working fluids were more responsible. Some users of POEs with HFC refrigeration systems switched to hydrolytically stable esters, but most stayed with conventional POEs with no problems.

Esters have been used in motor oils for some 38 years now without hydrolysis problems.

Tom NJ

 

[engineerscott]

TomNJ,

I read your write-ups on polyolesters and they were most informative. You've convinced me that hydrolytic stability is not an issue to be concerned about.

One other question concerning biodegradability comes to mind. Given that microbes can exploit the ester bond to break down POEs, is this in general a problem in an automotive crankcase environment? My expectation would be that for a regularly drive car this would not be an issue as the oil would reach a temperature that would essentially sterilize the crankcase lubricant any time the oil came up to operating temperature, and as long as you are driving the vehicle on a reasonably routine basis (say once a week or more) there would not be enough time between sterilization events for the microbes to make much headway.

However, what about the case for a car with a POE based oil in the crankcase that sits idle over the winter months (about 4 months where I live)? Certainly there is more opportunity for microbial activity to take hold in the crankcase during these longer idle periods, but in practice is there any evidence that this is an problem?

My guess would be that modern POEs which are more hydrolyticly stable are also going to be more resistant to microbial breakdown. Would you know if there's any evidence to back up this guess or, more importantly is it something to give any thought to for POEs in at all.

Lastly, if a person had a car running POE based crankcase lubricant that sat idle for extended periods, would a UOA be able to detect breakdown due to microbial activity if in fact there is a chance for this to occur?

Thanks for your informed advice.

Regards,

Scott

 

[Tom NJ]

Hi Scott,

The chemical environment in the crankcase is not conducive to microbe growth and therefore biodegradation. I wouldn't worry about it at all. Biodegradation requires lots of water and microbes, such as is found in wet soil and streams.

The only by-product of the biodegradation of POEs that could show up in a UOA is the acids, as increased TAN. But even them it would likely not show as the levels would be very low (little water present) and they would react with the reserve alkalinity.

Tom NJ

 

[engineerscott]

Thanks Tom. I didn't expect that it would be an issue but I had to ask. One might be tempted to say that were cost vs return not a consideration, that POEs might be the gold standard of automotive lubrication. But of course, how often is cost vs return not a consideration?

 

[Tom NJ]

Originally Posted By: engineerscott
One might be tempted to say that were cost vs return not a consideration, that POEs might be the gold standard of automotive lubrication.


Perhaps, but they are not perfect. The "advanced" POEs that offer the highest oxidative stability, cleanliness, and hydrolytic stability, also sacrifice some low temperature properties to achieve this. Blending in some PAO will restore the low temperature flow and help balance the effect on seals. A blend of advanced POEs, high lubricity POEs, and some PAO, may be the ideal, but also expensive and overkill for automotive engines.

Tom NJ

 

[Izb]

I am less concerned about the degradability of POE in the presence of moisture.
But would the moisture in the oil (my car is in cold parking 5 days a week in winter) lead to corrosion in the engine?

 

[bmwtechguy]

Not sure if this is an option, but have you considered any of the Amsoil producs such as their z-rod 10w-30? It has extra anti-corrosion additives for cars that often sit idle. As another option, a quality hdeo such as Rotella T-5 10W-30 would probably do the job for a lot less. I personally like and use Schaeffers hdeo 10W-30, another syn blend.