🔧 Technical GMT-800 Oil Consumption

[Outlaw]

So I’m looking for some ideas/ advice for my trusty steed. My ‘05 Yukon has been getting rapidly worse with oil consumption as well as smoke on startup. I’m having to add around 4 quarts during a 5,000 mile oil change interval. The smoke on startup has gotten easily 3-4 times worse than its ever been within the past week. It is usually the worst after driving for a while, letting the truck sit for 2-3 hours and then starting back up, but isn’t great on a cold start. Nothing noticeable on hot restart after 30-40 min or less though.

I work the shit out of this thing. It tows a small trailer almost daily and plows snow all winter. It runs buttery smooth, has no engine lights (active, soft codes, etc), is not down on power whatsoever, still pulls high 17’s to the gallon on the highway and makes 42psi hot oil pressure at idle and north of 60 at 2,000 RPM’s.

With that said... it has 298,000 miles and 10,100 engine hours. Am I right to suspect it’s not engine hard parts related getting so much worse so quickly? From what I’ve heard a faulty PCV valve could cause smoke on startup? These are integrated into the drivers side valve cover but a set of VC gaskets would do it right as well.

Im perfectly OK with adding 2qt’s of oil every 2,000-2,500 miles since it just gets the cheap shit anyways, but if there’s something to be done I’m all ears. I’d hate for it to start causing other issues like clogging cats and shit (if that’s even a thing)... I’m trying to nurse this thing along as long as possible within reason as a daily and then probably as a dedicated plow truck.

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[Outlaw]

I’m pretty much trying to get another year out of this one. By that point I’m hoping gas is $4.00/gal and we’re in another recession so I can get another one from CA or AZ for not $10,000.

 

[DEEZUZ]

I'm thinking valve seals along with worn pistons and rings.

I'd use a BG flush to try to Clear some carbon off the rings. They are probably gummy.

 

[CMNTMXR57]

Yea, valve seals going are a sign of the cold startup puff.

Not overly difficult to do on these engines, but time consuming.

 

[Outlaw]

I'm thinking valve seals along with worn pistons and rings.

I'd use a BG flush to try to Clear some carbon off the rings. They are probably gummy.

I’m wondering if the gummed up rings are what was keeping it kosher lol. I got in it to pass someone for the first time ever and it was coaling harder than my 7.3 in the tow tune.

 

[Outlaw]

Yea, valve seals going are a sign of the cold startup puff.

Not overly difficult to do on these engines, but time consuming.

I figured some was valve seals. I know that’s pretty much par for the course. I’m sure some of it is that, I’m just curious if anyone has ever seen the PCV cause excessive consumption.

 

[Turbocharged400sbc]

Your oil rings are probably full of carbon So your second and top ring are trying to be the oil scrapers and failing.

This mostly stems from the fact that the oil rings are barely big enough for brand new engines. they don't work so well when they can't flow any oil to the skirt drains.

I've noticed the same thing with cylinder number 4 on our 3800 if you were to pull your engine apart right now you would find oil behind the top compression ring. Our engine we have the excuse of a giant hole in the windage tray preventing removal of excess oil before it is slung onto the cylinder four bore wall.


Intake valve seals usually aren't that hard to see with just a borescope.... and they are probably the easiest and cheapest first step. Likely you'll at least reduce your oil consumption by 1/3.
200k is alot for the viton rubber seals (the steel bonded or the spring clip retaining styles)

 

[Outlaw]

I’m a weekend away from 300k lol, so I’m sure there’s some worn components.

 

[Turbocharged400sbc]

yeah, low tension/thin piston ring sets are great for reducing internal friction and increasing fuel econ....but arent great for long term durability.

 

[DEEZUZ]

I’m a weekend away from 300k lol, so I’m sure there’s some worn components.

You can do valve seals without major tear down. Move each piston to the top, make a air fitting from old spark plug and throw it into cylinder to hold the valves up. Use a spring compressor and disassemble the spring and locks, pull valve seal off, pound new on

 

[Turbocharged400sbc]

Make sure you use the install sleeve.
the valve stems will be mushroomed at the top and at the keeper grooves and will likely slice all of the sealing ribs off of the new seals if you do not use the install sleeve

 

[Outlaw]

So maybe it wasn’t burning as much oil as I thought. It burned 3.5qt over 5,000 miles if my math was correct. Going to pay more attention this go around.

Also running 15w40 this go around. I was running 5w30 prior, wanted to bump to 10w40 but they were all out and I have bulk 15w40 so diesel oil we get.

And just for my recollection.

4qt doesn’t show on the dipstick, 5qt shows 1/3 of the way up the hash marks, 6qt is at the top. Going to check it every 1,000 and add to the top of hash marks as needed out of a full 4qt jug over the 5k interval. If I don’t write it out somewhere I’m going to forget my super accurate scientific process.

 

[boostedguy05]

But what brand. Mobil 1 is the best

 

[Turbocharged400sbc]

5w40 rotella
Just make sure you always check it at the same interval and "settling " time.
the best is in the morning in your normal parking spot that way consistency is assured

 

[Lead Pipe]

Not sure if it would help but with a faulty PCV maybe bypass it with a catch can and breathers. Cheap and easy to do.

 

[CMNTMXR57]

Most oil consumption testing is done at 1,000 mile intervals.

You can easily tell if a lot of oil is being fed back in to the intake by looking at the back side to the TB blade and bore as well as shining a light in the TB. If you see oil puddled in the bottom of the intake, you know that's a source of the consumption too.

 

[Rdrnnr]

Put a catch can on it and send it

 

[Turbocharged400sbc]

You can't burn any oil if your engine doesn't have any oil in it

 

[CMNTMXR57]

So when our van was burning 4 quarts of oil on a 5 quart sump in 2,000 miles, I was on the phone with a Chrysler customer care rep for the umpteenth time explaining the fucking situation and she started spouting off about how much is considered normal for the mileage, I quipped "well, I guess I don't need to worry about changing it, do I? It'll just burn it all off. Just keep topping it off..." She wasn't amused.

 

[Outlaw]

Update:

15W-40 was promising but the engine just didn't like it. Lifter noise was far more pronounced. Switched to 10W-30 Rotella diesel oil the past two changes and consumption was cut in half from 5W-30 and shut the lifter noise up.

Currently sitting at 312k, haven't driven it much since I got the Prius, but it'll be getting the plow hooked up here shortly for the winter.

Another thing I've noticed with the smoke on startup, it definitely is made far worse when I don't let the fuel pump prime for a few seconds before cranking it over. Smokes and idles for a few seconds like it's got bad intake gaskets when you just go straight to cranking it., but if you let it build fuel pressure it's perfectly fine, no smoke.