Oil Viscosity trial and error

[Mudsport96]

That... is a whole lot of oil consumption.
You need to do a compression test before anything else. You are eating more oil than my 420k mile 5.3.
Pull the injector fuse and unplug the power to the coils before testing. Then get back to us with some numbers. This sounds like bad rings to me.
How are you mpgs?
Does the rig seem down on power?
I did the math here. And if you get similar mpg to my tahoe, a 300 mile trip SHOULD use about 16.5 gallons. And a quart of oil burnt in the same distance would give you roughly a 60:1 ratio fuel to oil. That is a little leaner than my Evinrude 115hp outboard....and it smokes good under load. So if you aren't seeing a constant smoke cloud, either your cats are catching it and are going to die soon, or you aren't burning it.
Pull spark plugs and take pics. If they look grey and ashy you are burning oil. Take note of the cylinders that look the worst. Check compression note the numbers.
That is about all I can help with. At the rate you are losing it, I don't think 20w50 would help.

 

[NardDog]

I really appreciate these suggestions and I have been thinking for the last year or so I would need to replace the valve seals.

 

[swathdiver]

let me preface this question by saying i have upgraded the valve cover and am currently running a oil catch can. My lm7 is still consuming more or less a quart every 300 miles, seems to vary depending on how much idling I do.

For those who are in the same boat(Valdez) have you found that topping oil with a particular viscosity weight or brand helps your engine consume less oil. Because Im using oil I dont use synthetics like mobile 1 . Im usually buying pennzoil or similar but a high mileage label. I switched between 5w30 and 10w30 with no noticeable difference. Winters aren’t really that bad here in Texas so I have not even accounted for them when buying oil.

Heres the question:
What viscosity do you thing burns more or less than others?

If theres seems to be an overall consensus on this topic i would like to know but maybe theres real way to remedy except for fixing the cause of the oil consumption(there its been said).

Well, first ensure that the oil you are using meets the specifications that GM established for your engine.

Second, I have found that engine oils with a viscosity rating of 11.5 or higher with regards to the ASTM D445 standard run better in my three LS engines. They do not rattle on start up and consume very little, if any oil between changes.

To be more specific, I am running ACDelco 10-9147 (5 Quart Bottle) and Quaker State 550046194 (5 Quart Bottle) in my trucks. We also change the oil between 4-5K miles. Old, dirty, worn out oil burns up and dilutes faster after 5K miles.

 

[NardDog]

Well, first ensure that the oil you are using meets the specifications that GM established for your engine.

Second, I have found that engine oils with a viscosity rating of 11.5 or higher with regards to the ASTM D445 standard run better in my three LS engines. They do not rattle on start up and consume very little, if any oil between changes.

To be more specific, I am running ACDelco 10-9147 (5 Quart Bottle) and Quaker State 550046194 (5 Quart Bottle) in my trucks. We also change the oil between 4-5K miles. Old, dirty, worn out oil burns up and dilutes faster after 5K miles.

This is the kinda data Iam after. I know i burn allot of oil but since I dont drive my truck daily It takes me a few weeks to before i need to top off.

 

[SnowDrifter]

This is the kinda data Iam after. I know i burn allot of oil but since I dont drive my truck daily It takes me a few weeks to before i need to top off.

Get a chance to do the 'driveway pcv test' yet?

While I think about it... Check the flow rate through your catch can too. If you're feeling brave, pull the hose off the valve cover and blow into it. System should be free flowing with no obstruction.

For what it's worth.. I run 0w40 euro spec oil in mine. Not sure what the special sauce is with the "euro spec" but it's given me the best lab results I've ever seen. Engine seems happy with it too.

 

[Mudsport96]

Another thing is you probably went to the newer style valve cover I am assuming. I went backwards to the 99 to 02 real pcv valve cover. No major issues with either of my 2006s.

 

[Marky Dissod]

Read this entire thread, noticed something missing: 12572717, if you're still using the PCV valve that rattles.

 

[catalinajack]

sounds like valve seals to me. at 200k you may as well toss new valve springs in there as long as they need to come off to to change the seals.

might want to do a compression test as well if the seals look ok. should be able to see em through the springs.

Something seriously wrong for quite a long time. Do as suggested concerning compression test. No alternative oil will solve this issue, ever. My 99 Tahoe with a 350 CID has 217,000 miles on the clock and uses virtually no oil. And, it runs like OEM.

 

[RET423]

How long ago did you install the catch can?
Is it installed correctly?
Is it a sealed can or a vented can?

It takes awhile for the oil control rings to free up and start working well after you install a catch can, especially if you didn't remove the intake and dump out the standing oil when the catch can was installed.

The catch can goes between the PCV valve and the manifold vacuum port, it should NOT be a catch can with a vented cap and the passenger side valve cover should remain connected as GM designed it.

At 200k I would run 15/40 or 20/50 on any engine that I care about, whether they consume oil or not.

And lastly, drive it like you stole it for awhile, if you are not comfortable with that loan it to someone who knows how to safely let that engine eat until you get the carbon burned out of the combustion chambers and the oil rings.

Your engine is packed with carbon deposits from eating oil and probably never being shifted beyond the automatics standard RPM range, I would bet it has plenty of life left in it if you give it the reins for awhile

 

[donjetman]

By now your piston rings are stuck. Do a piston/combustion chamber soak. Worked for me 5 yrs & 65k miles ago. Still going strong and no consumption.
Here's a thread I did back then:
https://www.tahoeyukonforum.com/threads/afm-piston-soak-top-cleaner.132134/#post-1650558
also improments have been made by GM to the pvc system. Install either a driver side valve cover GM# 12570427 or a pcv valve GM# 12572717 (fixed orifice).