Engine oil disappear question

[Jesseyourcalipers]

1999 gmc Sierra 1500 with a 2003 4.3 engine. Absolutely no leaks from anywhere. Zero smoke out of exhaust. And okayish compression on each cylinder being 155 across the board does that mean the piston rings are probably not wrecked? Motor oil keeps going low after about a week. Would bad pcv grommets cause that? Pcv valves and elbows are new just didn’t replace the grommets

 

[vavavroom]

Pull the spark plugs and look for fouling and oil on the threads from blowby.

Even if you don't see drips on the ground you may want to crawl under the vehicle and check if there are signs of leakage.

 

[Propflux01]

Possibly valve guides bad. You wont see smoke on those except a burst during acceleration after a longer idle period or deceleration (like down a long hill, or using engine to brake vehicle). You probably wont see it because its not enough at speed to see, unless someone is directly behind you. Oil tends to "disappear" because you don't actually see much, if any smoking. Unlike piston rings that usually smoke badly. I'd do a leak down to see exactly where the compression is leaking from. Excess oil being sucked into the manifold from blowby will have similar symptoms.

 

[spasm3]

Valve guides/seals. My dad's s-10 4.3 needed valve seals , as it is was fouling a plug. Seals fixed it.

 

[Jesseyourcalipers]

Pull the spark plugs and look for fouling and oil on the threads from blowby.

Even if you don't see drips on the ground you may want to crawl under the vehicle and check if there are signs of leakage.

I just did some front differential work for my off road trip. Zero oil from the pan or the valve covers and rear main seal just replaced it few months ago.

 

[Jesseyourcalipers]

Pull the spark plugs and look for fouling and oil on the threads from blowby.

Even if you don't see drips on the ground you may want to crawl under the vehicle and check if there are signs of leakage.

Also just did plugs they were dusty pink color burning surprisingly good

 

[Jesseyourcalipers]

Possibly valve guides bad. You wont see smoke on those except a burst during acceleration after a longer idle period or deceleration (like down a long hill, or using engine to brake vehicle). You probably wont see it because its not enough at speed to see, unless someone is directly behind you. Oil tends to "disappear" because you don't actually see much, if any smoking. Unlike piston rings that usually smoke badly. I'd do a leak down to see exactly where the compression is leaking from. Excess oil being sucked into the manifold from blowby will have similar symptoms.

I have heard of blowby burning oil. Like the hot gases evaporate the oil in the crankcase? And the oil vapor or smoke just finds ways out like the dipstick? It’s possible to disappear 1.5 quarts of higher viscosity oil with Lucas stabilizer in one week like this? Way In over my head with this. Not the ideal situation with so many other stuff going on currently. Might just head to mechanic shop

 

[Chris142]

Valve guides/seals. My dad's s-10 4.3 needed valve seals , as it is was fouling a plug. Seals fixed it.

X2.

 

[spasm3]

I have heard of blowby burning oil. Like the hot gases evaporate the oil in the crankcase? And the oil vapor or smoke just finds ways out like the dipstick? It’s possible to disappear 1.5 quarts of higher viscosity oil with Lucas stabilizer in one week like this? Way In over my head with this. Not the ideal situation with so many other stuff going on currently. Might just head to mechanic shop

Leave the lucas out. Have you been using lucas all along?

 

[Propflux01]

I have heard of blowby burning oil. Like the hot gases evaporate the oil in the crankcase? And the oil vapor or smoke just finds ways out like the dipstick? It’s possible to disappear 1.5 quarts of higher viscosity oil with Lucas stabilizer in one week like this? Way In over my head with this. Not the ideal situation with so many other stuff going on currently. Might just head to mechanic shop

Usually it will get sucked from the blowby in the crankcase, into the PCV valve, and into the intake. It will act similar to worn valve guide seals as far as smoke being seen is concerned. Hence why I recommended doing a leakdown test to be sure what's letting oil by.

 

[spasm3]

1999 gmc Sierra 1500 with a 2003 4.3 engine. Absolutely no leaks from anywhere. Zero smoke out of exhaust. And okayish compression on each cylinder being 155 across the board does that mean the piston rings are probably not wrecked? Motor oil keeps going low after about a week. Would bad pcv grommets cause that? Pcv valves and elbows are new just didn’t replace the grommets

OP what part of the country do you reside, Or what are your cold weather temps?

 

[meep]

Another vote for valve guides / seals.

 

[spasm3]

It’s possible to disappear 1.5 quarts of higher viscosity oil with Lucas stabilizer in one week like this? Way In over my head with this.

I hate to to tell you this,but depending on your climate, how cold it is, Lucas stabilizer could contribute to the problem.
It's a massive thickener with no additives so I thickens your oil especially in cold weather. Oil that's too thick when cold , might not lubricate the valve guides ,wearing them out. combine that with the product diluting the oils add pack i.e. moly , zinc, etc.Then as the oil does get warm it goes right down the valve guides, especially when the engine vacuum is high. I.e. off the throttle coasting to a stop.
You don't see much smoke ,because the engine has enough compression to burn it cleanly. As opposed to worn rings where compression is low and smoke is evident.

I would try a set of valve seals first, after dumping the " stabilized oil ".
If that fixes the problem, use just motor oil from here on out.
If it doesn't, you may need to have the valve guides knurled or replaced. Either way, don't stabilize the oil.

 

[clinebarger]

Leaking Intake Gaskets can also cause oil consumption if the vacuum leak/s are in the lifter valley. A '99 4.3L will have good positive valve seals & the guides are pretty durable.....Usually on the tight side if anything.