What causes sticking piston rings? And do diesel engines suffer from it?

[jtay2024]

Hi All,

Basically the question is the one in the title of this post. What causes sticking piston rings, and is it an issue that can occure on diesels? Are there steps that can reduce the chances of it happening? Driving style, oil choice & change frequency and fuel type I'm guessing are the biggest variables.

Does driving consistantly steady (efficient) increase the chance of it happening?

Thanks.

 

[Passport1]

Carbon in the grooves the rings fit into. The cause is 98% of the issue and debate.

 

[Jetronic]

It's not a widespread issue on diesel engines, but then those see different temperatures around the top ring, have no fuel mixed in with the oxygen between piston and piston wall, and they run diesel oils which are designed to keep soot in suspension.

 

[twX]

Diesel oils tested to API CJ-4 or CK-4 need to pass two tests designed to accelerate piston deposits and ring sticking, D6750 and D7549. These tests operate the engines at high speed and high load for hundreds of hours, so I'd imagine these conditions are what would promote deposit formation and ring sticking. Driving in a fuel efficient manner and changing the oil often enough are probably best for preventing ring sticking.

 

[bullwinkle]

Diesel engines that are operated without reaching full operating temperature, and/or short tripped-OR operated with the wrong rated oil or overly long OCIs, are more prone to sticking rings.

 

[JohnnyG]

This is quite a complicated issue. One that GM learned the hard way when they move the top ring very close to the top of the piston, then found out the oils at the time couldn't take the heat.
Diesels are also driven much differently that cars. I noticed on my Mercedes that the automatic transmission will downshift as I slow for a stop. I can watch the tachometer jump before hitting brakes or anything.
This is actually helpful in keeping the rings freed up.

Diesel OTR trucks are downshifted a lot.

 

[jetman]

Hi All,

Basically the question is the one in the title of this post. What causes sticking piston rings, and is it an issue that can occure on diesels? Are there steps that can reduce the chances of it happening? Driving style, oil choice & change frequency and fuel type I'm guessing are the biggest variables.

Does driving consistantly steady (efficient) increase the chance of it happening?

Thanks.

2016 Cummins and Valvoline got together and developed an oil to clean deposits from piston ring grooves and tops. See technical service bulletin TSB# 150163. The engines where the ISX15 & QSX15 that were suffering from early life oil consumption issues. I'm sure there are many more.
The oil was Valvoline Premium Blue "Restore" 10w-30. They quit selling it around 2020.
I found 4 gals of "Restore" and I'm currently using a 1/3rd mixture of it in my gasoline daily driver.

 

[andrew_j]

Bad engine design. /thread

 

[doublebase]

It's not a widespread issue on diesel engines, but then those see different temperatures around the top ring, have no fuel mixed in with the oxygen between piston and piston wall, and they run diesel oils which are designed to keep soot in suspension.

Why would they have no fuel mixed in between the piston and cylinder?

 

[ARCOgraphite]

Why would they have no fuel mixed in between the piston and cylinder?

Late Injector timing similar to spark timing - remember this is C.I. not S.I.

 

[doublebase]

It is interesting that you don’t hear about diesels having these ring issues (stuck rings/oil consumption). Can it because diesels have stronger tension on their rings, which enables them to be able to force their way out, and past carbon buildup on the grooves?

Some of these DI gas engines have these small thin rings on the pistons, and they are so stuck in their grooves that they simply won’t come out. Add I’m the oil control rings, which aren’t that robust nowadays either, with not enough drain back holes...and those control rings are getting stuck too. We’re talking three different rings sometimes getting stuck on some specific engines. All leading to blow by, carbon buildup, oil consumption, oil tracking back up into the intake manifold, oil consumption of 1 quart per 1,000 miles (or more). It’s a lot. There’s a lot going on here on some engines. I’ve seen engines so bad that the oil was actually pooling up into the air snorkel and into the throttle body, filling the intake manifold up with a pool of oil. ripping through a quart every 500 miles. And the PCV system is totally fine. Twofold...oil coming at that cylinder from the top and the bottom.

 

[doublebase]

Late Injector timing similar to spark timing - remember this is C.I. not S.I.

Ok thanks!

 

[BMWTurboDzl]

Hi All,

Basically the question is the one in the title of this post. What causes sticking piston rings, and is it an issue that can occure on diesels? Are there steps that can reduce the chances of it happening? Driving style, oil choice & change frequency and fuel type I'm guessing are the biggest variables.

Does driving consistantly steady (efficient) increase the chance of it happening?

Thanks.

The cause is design choices made around the area of the oil control ring at the piston. Diesels don't typically have this issue. Aside from manufacturing defects you can only keep up with your oil changes and occasionally take the vehicle out for a run on the highway if you don't during your day-to-day driving.

Edit: If you're following the manufacturers extended OCI you could try a product like Liquid Moly Engine Flush. They state it allegedly helps free up stuck rings. LM is readily available in the UK.

 

[Jetronic]

Why would they have no fuel mixed in between the piston and cylinder?

There is pure air blown into the cylinder, which gets compressed and only then is fuel injected which burns immediately.

Now, egr means there could be soot mixed in the air and dpg regens could cause fuel spray during the exhaust stroke but neither are a given: depends on how well the system is designed.

 

[doublebase]

There is pure air blown into the cylinder, which gets compressed and only then is fuel injected which burns immediately.

Now, egr means there could be soot mixed in the air and dpg regens could cause fuel spray during the exhaust stroke but neither are a given: depends on how well the system is designed.

I guess I don’t understand how that is much different than a gas engine DI system...”clean“ air enters the cylinder, with less than 10% EGR gas.

So, you saying the difference is the timing of when the fuel is delivered and burned? With a diesel the fuel is delivered AFTER the air is compressed on the compression stroke? and from there it burns instantly? whereas on a gas DI fuel is delivered sooner? Maybe as the piston is making its way up on the compression stroke and the spark plug then fires slightly before TDC?

So, less fuel is allowed to sit around in the cylinder, be forced down into the ring land area (during compression), and accumulate soot/carbon? That what you’re saying? If so, why can’t this be done on a gas engine?

 

[Lubener]

Hi All,

Basically the question is the one in the title of this post. What causes sticking piston rings, and is it an issue that can occure on diesels? Are there steps that can reduce the chances of it happening? Driving style, oil choice & change frequency and fuel type I'm guessing are the biggest variables.

Does driving consistantly steady (efficient) increase the chance of it happening?

Thanks.

Low tension rings are prone to sticking issues.

 

[Skippy722]

I guess I don’t understand how that is much different than a gas engine DI system...”clean“ air enters the cylinder, with less than 10% EGR gas.

So, you saying the difference is the timing of when the fuel is delivered and burned? With a diesel the fuel is delivered AFTER the air is compressed on the compression stroke? and from there it burns instantly? whereas on a gas DI fuel is delivered sooner? Maybe as the piston is making its way up on the compression stroke and the spark plug then fires slightly before TDC?

So, less fuel is allowed to sit around in the cylinder, be forced down into the ring land area (during compression), and accumulate soot/carbon? That what you’re saying? If so, why can’t this be done on a gas engine?

Automakers have tried getting HCCI gasoline engines to work, but they’re very finicky, changes in atmospheric pressure can be the difference between a smooth running engine and one trying to grenade itself with pre ignition.

Mazda twisted that idea, creating a SPCCI, Spark Plug Controlled Compression Ignition, engine. That works by putting an extremely lean fuel air ratio into the cylinder (30:1+), compressing the heck out of it, then spraying just a tiny bit of fuel near the spark plug and igniting it, which then causes the rest of the fuel already in the cylinder to combust.

 

[Jetronic]

I guess I don’t understand how that is much different than a gas engine DI system...”clean“ air enters the cylinder, with less than 10% EGR gas.

So, you saying the difference is the timing of when the fuel is delivered and burned? With a diesel the fuel is delivered AFTER the air is compressed on the compression stroke? and from there it burns instantly? whereas on a gas DI fuel is delivered sooner? Maybe as the piston is making its way up on the compression stroke and the spark plug then fires slightly before TDC?

So, less fuel is allowed to sit around in the cylinder, be forced down into the ring land area (during compression), and accumulate soot/carbon? That what you’re saying? If so, why can’t this be done on a gas engine?

yes, correct. On a gas engine you need a thorough mixture to get a combustible mixture. Too much gas and not enough air surrounding the molecules means the mixture won't burn, not enough gas and the flame dies out. Diesels are different, they don't need a flame to propagate, the temperature inside the cylinder is enough to get a burn. You can burn as lean as you want or as rich as you want. also note that diesel engines run significantly leaner mixtures, 18:1 is about as rich as they go unless running coal, where a gas engine could be running 12:1 or even richer during accelleration.

It would be possible to run a diesel engine on gas, but starting it will be harder (not enough heat on a cold engine) and you lose fuel efficiency. The fuel injection equipment won't last either.

 

[ARCOgraphite]

I guess I don’t understand how that is much different than a gas engine DI system...”clean“ air enters the cylinder, with less than 10% EGR gas.
... .... .

So, less fuel is allowed to sit around in the cylinder, be forced down into the ring land area (during compression), and accumulate soot/carbon? That what you’re saying? If so, why can’t this be done on a gas engine?

Some D.I. gas engine do this, why they can run 12:1 compression ratio on regular fuel.

Puff a lean mixture - say 30 deg ABDC - then puff a rich pocket near the spark plug 40 deg BTDC and have a stratified charge with an ignitable mixture.

But who says gasoline "pooling" between the crown and top ring doesn't do some beneficial cleaning? Or is it just making gum with the oil wash in that hot area with a partial burn-off?

Not enough "gettin' on the motor" these days to keep things clean; and the more powerful they are the less they will be exercised.

A self-fulfilling prognosis?

-Ken

Maybe we need Lake Speed Jr. on here to help us understand.