How common are stuck rings?

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One of the questions posed was, is oil control ring sticking more common these days and if so why?

If you hypothesise that oil control rings are stuck as a result of burning oil that goes through the PCV system, then three factors might logically impact on oil loss; engine oil volatility, blow-by gas flow rate and blow-by gas temperature.

If you put aside the impact of oil volatility and focus on blow-by, one might expect both flow rate and temperature to increase with compression ratio. Just out of curiosity, I Googled the compression ratio of all the cars I've ever owned. Is it just me or do I see a progressive trend to higher compression ratios and could this be contributing to higher levels of oil loss (and by inference, higher risk of stuck oil rings), regardless of oil volatility?

Morris 1100 1.1L (1978) 8.5:1
Fiat Mirafiori 1.2L (1980) 9.2:1
Austin Maesrto 1.3L (1985) 9.8:1
Honda Accord 1.6L (1987) 8.4:1
Toyota Carina 1.6L (1990) 9.4:1
Toyota Corolla 1.4L (2002) 10.5:1
Daihatsu Sirion 1.0L (2006) 10.5:1
Kia Picanto 1.0L (2014) 10.5:1
Suzuki Celerio 1.0L (2016) 11.0:1
 
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Originally Posted By: SonofJoe
... If you hypothesise that oil control rings are stuck as a result of burning oil that goes through the PCV system, ...
Would it be reasonable to hypothesize similarly in regard to plugged piston drain holes?
 
Originally Posted By: SumpChump
I own a oil drinker the Toyota 2AZ-FE in a 2008 Scion xB at 140k miles. Adult owned previously and 5,000 mile documented OCI. But with conventional. The oil return holes coke up. I WISH that I has just stuck rings. LOL

I''m interested to see how long she goes till she blows or more likely the catalyst clogs up which I will the tear off and "replace".

In any case, I hope it lasts two to three years so I get the monthly cost of ownership down to about $150 per month.


Same engine as mine and roughly about the same mileage. Only difference is used synthetic since I got it at 13k miles. Oil never moves on the dipstick in a 5k OCI. I think that is the difference. Plus most of mine is highway mileage.
 
Originally Posted By: CR94
Originally Posted By: SonofJoe
... If you hypothesise that oil control rings are stuck as a result of burning oil that goes through the PCV system, ...
Would it be reasonable to hypothesize similarly in regard to plugged piston drain holes?


In a word, yes.

The table suggests that engine compression ratios have increased over the decades. All my cars have been naturally aspirated. Throw in the trend to use turbochargers and superchargers and this trend goes even further.

One could reasonably overlay on this, an increase in oil Noack volatility. My old 1100 would have been specified with a full mineral 20W50 (typical Noack of 5%). The Carina would have used 15W40 (typical Noack 7%). I'm guessing the Corolla would have used 10W40 (Noack of 12.5%). My latest car, the Celerio, specifies full synthetic 0W20 (Noack 11.8%). Accompanying this trend would be a gradual shift to lower aromaticity/lower solvency base oils.

Furthermore, you might imagine that the amount of metal sealing the combustion chamber has decreased. By this I mean the thickness of piston rings has decreased as has the tension they exert. I noticed this first on my Sirion which made big claims for fuel economy via low friction, low tension rings. It was the first car I ever owned which consumed oil.

Put all of this together and you might imagine a scenario where higher compression ratio engines with less inherent cylinder sealing create more blow-by gas which is fundamentally hotter, which interacts with higher volatility engine oil to push more evaporated oil through the PCV system to be burnt. As this oil burns badly, it leaves behind more heavy gunk which is fundamentally less soluble in the base stock.

Could the end result be more stuck oil rings and plugged drain holes which in turn create excessive oil loss? To me, this sounds all too plausible...
 
Could this be the reason that 20W-50 was the recommended grade for so many cars sold in the EU up into the nineties? Most of these engines would have had 10W-30 recommended in this country and most of them didn't make enough power to hurt themselves.
Given the entirely plausible scenario you've sketched out, what changes in oil used or OCI might ameliorate this?
 
Piston rings are spring loaded and therefore need to be able to float in their respective rings lands so that they can expand and contract under spring tension. When the oil drain holes in the ring lands get plugged up, the oil gets cooked in there and solidifies. The end result are piston rings that are wedged in there and not able move freely so that they can exert force against the cylinder wall for creating the seal. At that point the oil sneaks by and gets burned in the combustion chamber.
 
^ I'm gonna go ahead and take that as a compliment.
grin2.gif
 
Originally Posted By: Merkava_4
Piston rings are spring loaded and therefore need to be able to float in their respective rings lands so that they can expand and contract under spring tension. When the oil drain holes in the ring lands get plugged up, the oil gets cooked in there and solidifies. The end result are piston rings that are wedged in there and not able move freely so that they can exert force against the cylinder wall for creating the seal. At that point the oil sneaks by and gets burned in the combustion chamber.


What drain holes? I have a 1.9 Saturn Twin cam oil coking engine.
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The brilliant engineers eliminated those pesky drain holes to ensure the engine had a long life (as long as you top off the oil). If you install drain holes and use an oil up to the high heat the engine creates the oil consumption problem stops.
 
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Originally Posted By: fdcg27
Could this be the reason that 20W-50 was the recommended grade for so many cars sold in the EU up into the nineties? Most of these engines would have had 10W-30 recommended in this country and most of them didn't make enough power to hurt themselves.
Given the entirely plausible scenario you've sketched out, what changes in oil used or OCI might ameliorate this?


One of the things I would dearly love to know is how engine oil usage has varied by viscosity grade over the decades for the different regions. My guess is that only the oil companies have this info and sadly they rarely share.

You're right about 20W50 being a major grade in the UK with Duckhams Q being the first and best known until Castrol GTX took over. Part of the popularity of 20W50 stemmed from the fact that it was used as a 'shared' engine & gearbox oil on Austin/Morris/BMC/Leyland engines (like my old 1100). That and the fact that it was cheap. I guess this changed in the '80s with the spectacular rise of the German OEMs who really took oil specs to the next level. Many of the defining features of Euro oil that were set back then, still persist today; 3.5 min HTHS, seal compatibility, dual petrol/diesel functionality, low Noack and the move to low SSI VIIs. Although it probably wasn't deliberate, it was the German requirement for 3.5 min. HTHS which stopped 10W30 becoming the dominant oil grade that it was in the US.

Regarding what could be done to stop modern oils contributing to oil ring sticking, IMO the first thing that should be done is for API/ILSAC to change their maximum Noack spec from 15% to 13%. Although, because of the complexities of this problem, you can get oil ring sticking in all sorts of circumstances, it's very likely that the majority of the problems in the US are caused by the highest Noack oils. That API/ILSAC will carry the 15% limit over into GF-6, when Dexos & all of Euroland specify 13% max, borders on the scandalous and smacks setting the rules to suit their own needs rather than those of their customers.
 
Originally Posted By: SonofJoe
...
Regarding what could be done to stop modern oils contributing to oil ring sticking, IMO the first thing that should be done is for API/ILSAC to change their maximum Noack spec from 15% to 13%. ...
How will that help if the oil getting coked in the ring lands and drain holes is coming up from below, not through the PCV path? Or is that somehow impossible?

What else do you suggest to minimize risk of sticking and coking in susceptible modern engines---for which 0W-20 is specified by the manufacturer in many cases?

Thanks!
 
Originally Posted By: Merkava_4
Piston rings are spring loaded and therefore need to be able to float in their respective rings lands so that they can expand and contract under spring tension. When the oil drain holes in the ring lands get plugged up, the oil gets cooked in there and solidifies. The end result are piston rings that are wedged in there and not able move freely so that they can exert force against the cylinder wall for creating the seal. At that point the oil sneaks by and gets burned in the combustion chamber.


I dont think you can be as definitive as to say it's a two stage process (as in first the drain holes plug and only then does the ring stick). If I'm right and this is an inherent lack of solubility thing, then the process is more likely to be akin to the furring up of a kettle with limescale. The drain holes will close up gradually with deposits already accumulating in the groove. However I suspect no-one knows the truth as this is probably the most under-researched topics in the industry.

A couple of things to add...

The first and second rings both rotate, move up and down in their grooves and expand and contract under chamber pressure. As such, the butt ends of the rings act as moveable groove scrapers and both rings can be considered as self-cleaning.

The oil control ring assembly, especially if it's a simple two piece ring is far less flexible. It's sole job is to exert a high force against the bore and scrape. Importantly it lacks the self-cleaning functionality of the top two rings. It also sits in the coldest part of the piston. Put all of this together and you can see why the oil control ring is so vulnerable to burnt oil deposits precipitating out of low solvency oil.
 
Originally Posted By: CR94
Originally Posted By: SonofJoe
...
Regarding what could be done to stop modern oils contributing to oil ring sticking, IMO the first thing that should be done is for API/ILSAC to change their maximum Noack spec from 15% to 13%. ...
How will that help if the oil getting coked in the ring lands and drain holes is coming up from below, not through the PCV path? Or is that somehow impossible?

What else do you suggest to minimize risk of sticking and coking in susceptible modern engines---for which 0W-20 is specified by the manufacturer in many cases?

Thanks!


I think to answer your question, you need to distinguish between the two sources of deposits.

The first and traditional source of deposits, comes from excessive base oil oxidation. This is where oxygen in the hot blow-by gas attacks the base oil (usually at the weak benzylic hydrogen sites) to form carboxylic acids which in turn condense or polymerise to form deposits.

This problem is worst in Group I mineral oils which still contain an appreciable amount of reactive aromatics. Traditionally you would tackle this with antioxidant-type additives & metallic detergents (as acid scavengers). In addition to this, typically you would run these oils to a short OCI and in effect, pull them before they 'over-oxidise' and drop stuff out of solution.

In the last couple of decades, especially in the US, we've seen Group I use in engine oil virtually eradicated as they've been replaced by Group II's (hydrotreated Group I's) and to a lesser extent Group III's (Hydrocracked Group I's). In both cases process hydrogen zaps the most reactive parts of the base oil making it much more resistant to attack from oxygen. In short, these oils are far more stable. Interestingly, Group II oils can contain MORE antioxidant than old Group I, even though they are more stable, because of the vagaries of the Teost test.

Now because Group II/III oils are very stable, they throw out very little by way of 'traditional' deposits; even when run out to longer OCI's. However because the I -> II/III base oil shift has coincided with the move to thinner, more volatile viscosity grades, these oils put more oil vapour into the PCV system which ends up getting burnt. Now unlike petrol, engine oil does not burn at all well and the burning process is likely to leave behind stuff that is likely to form deposits.

This second source of deposits is very different to the first traditional source. It will be totally unaffected by the additives in oil and can form from Day 1 of the life if the oil. In fact, it's quite possible that very stable Group II/III oils burn less well, and create more deposits than old fashioned Group I's because the act of burning something is just an extreme form of oxidation reaction. And this is where the poorer solvency of Group II/III oils could potentially hurt you because these deposits will have strange properties. They aren't 'traditional' condensation/polymerisation products, they probably aren't even like diesel soot and there's probably nothing in the oil other than base oil solvency that ultimately stops them coming out of solution.

So in answer to your question, the logical way to stop oil ring stick is to try and restrict the burning of PCV oil by restricting Noack.
 
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