I just got back from vacation last night and drove about 600 miles each way. I check the oil when I stop at gas stations because the ol girl usually likes to eat a little oil- usually a quart around every 800 miles. I noticed on the way there and back I didn't use a drop. I changed the oil the day before I left and it was the on the exact same place on the dipstick when I got there. Same on the way back. I was cruising up I75 99% of the trip between 65-75 mph. Here's what I know:

- fixed plenum gasket/aftermarket pan last year and it's still good
- compression on all cylinders was around 160 dry except #7 was 140 dry, 160 wet and #8 was 120 dry, 145 wet
- does not smoke on initial start up; hot or cold
- only visible smoke is at idle then when I take off there's a puff of smoke and that's it; no visible smoke after that
- I have true duals and no cat and it smokes equally out of both tailpipes at idle

It seems like it only uses oil when the engine is at idle speed. Any ideas on what could cause this? Could it just be the rings on #7&8 cylinders? Thanks.

 

Rings or valve seals.. Have you done another compression test? Any way you could do a leakdown test?

 

I would lean more towards valve seals. At idle, manifold vacuum is highest, and has the greatest opportunity to suck oil down the intake valve guides. Not to mention that the stock seals are probably dry, and brittle from age..... I.E. Not doing their job anymore.

 

I don't have a leak down test kit but I might get one next time I'm by Harbor Freight. dlyter those were my 2 thoughts as well- especially since the compression came up so much when a little oil was added to the cylinders. I was always under the impression that usually when valve seals were leaking is when you would get that puff of smoke when you first started it- at least that's the way all my Chevy's were lol. Heyyou I was thinking it probably had something to do with vacuum as well since there was more at idle; so valve seals make the most sense. I just didn't want to take the time to do them if it wasn't likely that was the problem. At least they're relatively cheap. That'll be the next thing on the list to do. I hate the truck blowing smoke- it makes me think that other people think it's a piece of junk lol.

 

With the right tools, (on the head valve spring compressor, and an air compressor, and the right fitting to pressurize the cylinder, to hold the valves closed....) the job is tedious, but, not really difficult. Don't be in a hurry though. If you drop a valve into a cylinder.... fishing it out is a bear, and usually leads to having to yank the head.

 

another method:
one cylinder at a time, and with all spark plugs removed, rotate piston down. feed in a generous amount of 1/8 - 1/4 inch soft rope into the spark plug hole. rotate piston up until engine stops. this pins the valve up in the head, allowing the springs to be unclipped and seals replaced.

 

This method actually works pretty good if you don't have air available. Use cotton rope. Any 'stuff' that stays in the cylinder will burn off quickly when you start the engine.

 

10-4. A buddy of mine has the adapter for the air compressor and the tool to compress the spring on the head so I'll probably try that route first. My brother just blew the engine in my parent's s10 so now I've gotta Yank that engine and find another one. You'd think people would have enough sense to stop when it starts smoking then knocking...

 

Nah, they don't wanna have to walk to the nearest phone, even when it is in their pocket...... They would rather make SURE they do a thorough job on blowing the motor.

 

Even better - he called my dad and dad was on the way to pick him up. He didn't feel like waiting because he was tired and hungry. The truck kept dying but he kept getting it started again. About 1/4 mile from the house something let go and shot through the oil pan. Made it about a block past there and locked it up. Coasted the rest of the way home. RIP iron Duke lol. Now he has to ride his motorcycle to work every day in the rain because my parents won't let him drive anything else