Sealing up worn 5.3l leading to oil burning?

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smb3

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I have an 06 Suburban with 265k miles. Original engine, and transmission. The engine has all the typical oil leaks, rear main, oil cooler port, etc. I had the valve cover gaskets replaced though. Does not burn oil currently.

My mechanic convinced me NOT to replace the remaining seals and stop ALL leaks and his reasoning was that on such a high mileage engine, sealing up the leaks would probably cause it to start burning a lot of oil. I'd rather a few drips here and there over burning oil. He said he had a customer come in recently with the same setup, insisted on replacing all seals, and now that person's truck burns a lot of oil.

I am starting to doubt it though, and couldn't find much info online to confirm whether this is true or not.

Can sealing up a high mileage engine cause it to start burning oil even if it is not burning any now?
 

Marky Dissod

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Can sealing up a high mileage engine cause it to start burning oil even if it is not burning any now?
Answer to that question is Maybe.
The next questions should be, 'Why might THAT engine burn oil, once the leaks get sealed'?
and
'Why might another otherwise very similar engine NOT burn oil, once its leaks get sealed'?

If the assumption is 'They ALL burn oil, unless they get to leak somewhere'
and that assumption turns out true, then I suppose I'd prefer leaks.
However, I'd still try to answer my first two questions in each other's context definitively, and learn why.

It might be worth it to seal it up and ALSO address the root cause of the oil burning.
MUST every GM V8 either leak or burn oil? Really? Why? 'They just do'?

I can say the following with some experience:
lowering GM's fan-on thresholds of my 9C1-LT1 Caprices invariably reduced oil burning considerably
using GM's PCV thingy 12572717 also helped reduce oil burning
an external 9C1-type air-to-oil cooler - NOT the one physically connected to the radiator - also helps
once using all of the above, my worst oil burning LT1 leaked & burned under 2 qt between 3500-mile oil changes.

That one stopped leaking AND stopped burning oil after installing a pair of catch cans -
One for the line between the valvecover and the throttle body
One for the line that sends crankcase vapors to the PCV Valve, which should be a 12572717.
 

Mudsport96

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First things first. My 06 Silverado smoked a bit when the father in law had it at around 270k miles. I went to the local junkyard and grabbed a diver side valve cover from a truck so i had the old pcv style cover. I soaked it a few days in mineral spirits to soften the gunk and then pressure washed it real good. Then opened up the drain back holes to twice the size of factory. It stopped smoking after it cleared the residual oil in the intake manifold. And it was fine for a long time started smoking again lightly around 400k on it so that is to be expected. I installed an amazon oul catch can and i empty it every few weeks. No more smoking as it keep all oil out of the intake tract. The dont seal it up statement boggles my mind, because it will burn oil whether or not the pan or rear main leaks, that makes zero sense. 20220204_120837.jpg
 

Marky Dissod

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I went to the local junkyard and grabbed a driver side valve cover from a truck so i had the old pcv style cover.
If the Gen 3 V8s prefer the 'older' driver side valvecover, then my next question - and I am not joking - is:
Why not TWO driver side valvecovers?
Then opened up the drain back holes to twice the size of factory.
This also sounds like a really good idea.
It stopped smoking after it cleared the residual oil in the intake manifold.
And it was fine for a long time started smoking again lightly around 400k on it so that is to be expected.
I installed an amazon oil catch can and i empty it every few weeks.
No more smoking as it keep all oil out of the intake tract.
Starting to think catch cans should be installed as soon as reasonably possible.
I'd prefer this kind of controlled leak to any amount / kind of leaking at any of the seals.
The dont seal it up statement boggles my mind, 'because it will burn oil whether or not the pan or rear main leaks'?
That makes zero sense.
Hear here. Don't just settle, fix 'em BOTH.
 

Mudsport96

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If the Gen 3 V8s prefer the 'older' driver side valvecover, then my next question - and I am not joking - is:
Why not TWO driver side valvecovers?
Because the passenger side cover is where fresh filtered air enters the crankcase to be pulled through the engine to the driver side. Where it then pulls the vapors out and into the intake to be burned. If you remove the fresh air source you create new problems.
 

Marky Dissod

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Because the passenger side cover is where fresh filtered air enters the crankcase to be pulled through the engine to the driver side.
Where it then pulls the vapors out and into the intake to be burned.
If you remove the fresh air source you create new problems.
OK, now I get it. Much appreciated.

Just learned that the latest Tahoe PPV 5.3L uses different valvecovers from the civilian 5.3L.
I wonder why?
 
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smb3

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Thanks everyone for the feedback. I must reiterate that It does not currently burn oil, but it does leak a bit from the rear main and oil pan and oil cooler cover. I would rather the leak than it to burn. What it sounds like to me though is that fixing a rear main and pan leak would never in a million years cause the engine to start burning oil. The two must be completely unrelated.
 

Marky Dissod

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My mechanic convinced me NOT to replace the remaining seals and stop ALL leaks and his reasoning was that on such a high mileage engine, sealing up the leaks would probably cause it to start burning a lot of oil ... He said he had a customer come in recently with the same setup, insisted on replacing all seals, and now that person's truck burns a lot of oil.
I must reiterate that It does not currently burn oil, but it does leak a bit from the rear main and oil pan and oil cooler cover. I would rather the leak than it to burn. What it sounds like to me though is that fixing a rear main and pan leak would never in a million years cause the engine to start burning oil. The two must be completely unrelated.
Your mechanic, however, is suggesting that they likely ARE related.

Hypothetical example:
A wee lil bit too much operational oil pressure pushes a lil bit of oil past the rear main, oil pan, and oil cooler cover.
You fix the leaks, but the slightly elevated pressure remains.
With nowhere else to go, the elevated pressure escapes into the combustion chamber and gets burned.

In this case the two most likely possible causes would be:
valve stem seals need replacing
piston rings need replacing
The third cause ... too much oil pressure.

I'd check the PCV system - maybe a valve cover needs updating?
Read this post again ...
 

Alex_M

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Sealing up oil leaks will not cause you to burn oil unless there is an issue with the PVC system allowing too much crankcase pressure to build up.

Too much oil pressure will not cause you to burn oil - there is nowhere that pressurized oil is in contact with a potential method of entry into the combustion chamber.

Agree, the two likely methods of entry are valve stem seals and piston rings *if* the PCV system is functioning correctly, but if either are bad then you should see some oil burning now. I would have zero concern that fixing oil leaks would cause my motor to burn oil.

Catch can is a good recommendation. New PCV valve is cheap, wouldn't hurt while a mechanic is in there sealing up leaks. You can also check your old one my shaking it. If the valve inside jiggles the PCV is good.
 

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