I know you guys like engine builds.
This is different.
I am trying to analyze an oil consumption problem.
300 miles per 1 qt.

Here is my question for engine experts:
Could very low tension oil rings cause the oil to slide by the compression rings and burn that much? 1 qt in 300 miles?

After tearing the engine down, I can not find any other "smoking gun" that might cause this.

It's not a corvette. It is my CTS daily driver. I have owned this for 15 of it's 17 years. I take great care of it.
It always used oil and was never better than 1500 miles/qt. Then it got worse and worse. Now it clogs the cats, won't pass inspection etc. Has 200k miles on it.
1 qt of oil for every tank of gas, ~300 miles.
It is a rare manual 6 speed stick Caddy so I want to save it. If it was an auto I would just send it....
So I took the engine apart. 3.6 DOHC GM LLT GDI
I am looking for the "smoking gun"
Maybe I found it.
I would like someone else with LS experience etc to weigh in, since it seems similarly built.

Things I checked to no avail:

• No smoke while driving or startup.
• No leaks.
• It still has great compression, but burns lots of oil????
• Great compression 185-195# in all cyl
• Great leakdown 3% on 5 cyls, 9% on one, cyl #4
• Some oil consumption thru PCV, some oil in the intake, and on back of intake valves. Less than it used to be.
• Modded the PCV system, less oil in intake, but no change in oil consumption.
• Pistons now out. ~1 thou bore wear, no cyl ridge. from 1.0 to 1.3, over max spec, 1 cyl at 1.7 wear #6
• New pistons are .0008" bigger, put cyl to bore back in spec ~2 thou, now 1.9-2.5 thou all cyls
• Less than .5 thou taper or oval shape
• Cross hatch still looks terrific. Almost zero scratches.
• Valve stem to guides worn ~.0005", still near mid spec
• Valve seals appear tight, hold valves up, still have sharp edge.
• Ring gaps not terrible, some wear, .014 top, .025 2nd, .022 oil still on high side of fact spec
• I fully expected the oil rings to be completely stuck, and plugged solid full of carbon. To my great disappointment, they were not. They still moved freely.
• So I am still looking for another reason it drinks oil.

Here is the ONE THING that might be it:

• Piston oil rings have almost no drag. Engine will free spin with one piston in. Measured 7# of drag with a fish scale for one piston, oil ring only.
• This is like a little finger push!
• Factory spec is 8-13# but is radial compression tension, not fish scale drag. Old school SBC oil rings are 20#. LS engines down at 11#.
• Old SBC 3/16" rings are basically 4.5mm. These are very thin oil rings, 2.5mm. Compression ones are 1.2/1.5 mm kinda like LS motors.
• New rings oil scraper is much tighter, 13# of fish-scale drag.
• Scraper on new oil rings is thicker than old, 0.150" thick metal vs .120" thick old. Torsion calculators online say this alone would account for the 7 to 13# drag difference
• I found at least one BBC drag race builder who targets 10-12# for oil rings. Another who says the low tension rings can free-up 25HP.
• Every thing I read online says lower tension rings are worth a few HP, but at some point are you too low, and get oil consumption. Is this 7# the "too low" point? Is 13# better? or enough?

So do you think I may have found the problem?

This engine is a "pain-in-the-neck" to work on, in chassis, and I would like to do this only once, without putting a torch to the car! LOL

I know you guys like pics:

Here is the best article I could find on the subject:
https://www.dragzine.com/tech-storie...-ring-tension/


The complicated long block


Terrific looking cross hatch even after 200k miles. Gotta love those low tension rings for this!


Old piston. Rings were not stuck. And end gap wear was not terrible. There is some crud on the tops, but I expected worse with the oil useage.


Backs of intake valve have some oil crud. It actually used to be thicker 100k miles ago.

There is only one old piston and 3-ring set left in the short block. Seems far too easy to spin.


Measuring Oil ring drag, old ones at 7#, new ones at 13#


New rings


This is the oil ring expander. The new Hastings rings the expander is measurably thicker. .150" vs .120" old.


Hopefully you enjoy the pics!

 

Sounds like a known issue with the 3.6 design.
Have you tried a Cadillac forum?
Read this found through Google
https://newparts.com/articles/common...%20oil%20usage.

 

Yes I have been active there for years.
No one there really tears into engines.
The PCV system has an issue, and has been addressed.
And "they" blame carbon coked rings.
But my rings were not clogged....
That is why I suspect another issue.

 

You have a lot of coked up oil on the valves. Not where oil should be.

I ran an inline PCV catch can for a while on my blown LS3. It did a good job of keeping the oil out of the intake manifold and off of the valves. It made a bit of a "rattle" at idle that i hated so I pulled it off. Maybe something like that would help keep oil out of your intake. It would be worth the effort if you could identify that as the cause of the oil consumption at a minimum.

 

I hear you. And I went down that road before .
This engine has almost a quarter million miles on it!
Yes the coked oil on the intake valves used to be twice as heavy until I did the suggested PCV mod.
I will be adding a catch can this time around. For testing anyway.

I just want to be sure I fix any potential ring issue, "while I'm in there" the rings seem SO LIGHT.

One reason I discounted the PCV as the source is I only ever hear of guys getting say 3 oz in their catch cans in 500-1000 miles. I am burning 1 & 1/2 quarts at that mileage!! I would fill a 3 oz catch can in 30 miles!

That's why I am thinking it has to be a bigger problem.

 

I would suspect lack of oil ring tension to be the problem.
There isn't much downside to increasing it. You're not looking for every bit of gas mileage like GM was.

 

My thoughts exactly.
I Had 7#.
​​​​​​new ones are 13#.
Thinking of getting a custom set at 15-16#.
Old school is 20-25#

I have never played with ring tension before.

 

Just because those catch cans only catch a dribble does not mean that was all the oil that was there.....

Cheap azz catch cans are not very efficent. Put an inline see-thru fuel filter after the catch can and see how well it works. Many cans do not.

Still, bad ring seal is bad, and can cause extra oil vapors in the PCV system. Re-ring it and add a good catch can is my advice. Moroso is nice and easy to empty. Probably better than the RX can I have.

 

Thanks!
I really know nothing about catch cans, but feel I need to try one.

 

My daughter's Camaro has the same engine and they do sometimes need a "catch can" to help keep the crud from the PCV system from getting into the combustion chamber. The backside of your valves is typical of what happens in the GDI engines. I use BG 44K fuel system cleaner as they claim it will remove the deposits on the valves.

The 3.6 seems like it could be a great motor to build upon, a nice little supercharger and it wakes that engine up big time. I just worry about those L-O-N-G timing chains wearing out along with the various tensioners.

 

So in the process of building a 406 and seeking advice here I was told to consider the pistons with thinner "LS" spec rings and I believe it was Jebby that stated he just built an engine for someone with them that he and the customer were amazed would spin over with one hand with much less resistance with al the pistons in place... I only mention this because you might be used to the resistance of the thicker rings found in older engines like the SBC. So the downside of this and is stands to reason may be that the thinner oil rings may become weaker that much quicker than what your used to.

 

hmm,
don't know your driving style but that engine needs to be beat on to control oil use.
the rings need to be forced to expand on "deceleration".
whenever mine shows oil use,
2nd gear hard accel and then let it use engine to slow car.

 

Yes I have read lots of threads on Speedtalk, etc. about running thinner rings, with less friction, and gaining 20HP on race engines.
Ring friction supposedly absorbs 15% of brake HP to overcome the friction. So 45HP @ 300HP, 60HP @ 400HP, 75 HP @ 500HP, etc.
You can cut that in HALF with these low friction rings. And gain 20-35HP to the wheels.
The manufacturers do the same thing to squeek out a little bit more MPG out of the engine.
Most of the engine builders on Speedtalk do not recommend going below the 8-10-12# range. More if using "power adders".
Once you go too low, oil consumption goes up dramatically.
I was at 7# with the old high mileage rings.
My new ones are at 13#.
Better.... but I do not have enough experience to know if it is enough. At least it is on the high-end of the GM specs.

GM had a lot of trouble with this on early LS motors and their new-at-the-time thin ring design.
This engine is from the same era.
So did other mfgrs. Honda had a huge problem with this for 5-6 years on a lot of their engines, replacing pistons & rings, under warranty conditions. A tech told me this.

The old school SBC 3/16" "thick" rings were up in the 20+# range. They did not have this ring-oil-burning problem.
In my opinion all these new cars burn more oil than the older generations did. 1000 miles / qt is considered "normal" now right?. It used to be 2x or 3x that.
IMHO I think the car mfgrs have taken oil ring tension down as low as they possibly dare, and have knowingly traded a little more oil consumption, for a little more MPG, to help meet Gov stds. And on any given engine, sometimes it is just not enough.

So 13# "MIGHT" be enough. GM specs are 8-12# for this engine.
But this is a whole lot of work to go thru if it doesn't solve it.
I would be much more comfortable with 13-17# on the oil rings, if I can get there somehow.
It might cost me 3HP, big deal. I currently need to buy $1600 worth of catalytic convertors that are ruined!

I may just buy a .010" larger ring set, just to get the bigger expanders. And run my own experiment.
Hmmm...

 

I'm curious about what weight oil you use in this engine? My thoughts are if you use a thicker oil with low tension rings, you could possibly be getting the rings floating on a thick hydrodynamic wedge of oil that's not being scraped away by the rings. Using a thinner weight oil may prevent this from happening.
Just a WAG on my part.....

 

Have to think The General was willing to sacrifice some oil consumption for a decrease in gas consumption. Those cylinder walls look like they just came out of a Sunnen honing machine.

 

My thoughts exactly! I have honed blocks, and this 220,000 mile block looks really good! Hardly any block wear, taper, etc.
So low friction does have it's benefits.
A lot of Honda engines were known for suddenly going from acceptable to horrible oil consumption with only .002" wear on rings, measured at ring gap.
I suspect mine is sort of similar.
My oil use was never great ~1500 miles, but slowly dropped to ~300 miles. Rings have only worn 6-8 thou (extra gap) and bores 1.5 thou.
Not really a lot of wear, but I guess it was enough to reduce the oil ring tension below "effective" levels.
The old oil rings are 7#.
The new ones are 13#.
GM / Hastings spec is 8-12#
So I still think the 13# is marginal.
I am thinking about getting that up to 16#+ and calling it a day.

Looks like I am going to experiment with stretching some oil expander springs!

 

Thanks guys!

I guess I just wanted to talk it over with a few of you and confirm I am on the right track.

 

IMO you're absolutely on the right track. I'd rather sacrifice a small amount of HP or fuel economy to prevent oil consumption and all of it's associated problems.
how much HP and fuel economy is lost with all the loss of flow across those contaminated valves and clogged catalytic converters?
OEM's don't concern themselves with that. only meeting fuel economy specs for government CAFE requirements at the time of testing.

 

The Picture of the Piston Top is that straight out of the Engine or has there been any cleaning done to it ? In the Pic there isn't any Carbon on the outer edge. A clear indication that the Carbon can't stick because its being washed with Oil coming past the Rings. I don't like the signs of Oil in the Intake. I wish you had run it for 300 miles with the PCV disconnected. It could also be a leaking intake gasket SBCs are famous for, but I don't know about that Engine. .

 

Now that was an astute observation!
That piston was cleaned a little.
The one below is more typical with no cleaning.


There is almost no carbon on the outer edge of the top, or above the top ring on the side.
And this on a 200k mile engine!
I agree "oil washing" is likely the cause of the clean piston edges.

I just got off the phone with Total Seal.
He agreed at my low 7# tension level he would recommend a vacuum pump, and for a race car only, and would not recommend that for the street.
I just ordered some oversize oil rings.
The larger expanders should increase the tension up to 15# or beyond.