Also, Chevron Delo 15w-40 is on sale at Walmart for $13.99 I believe.

Those numbers though not high are consistent as stated before.

I'd try 5 quarts with 1 quart of MMO.

 

So a 15w-40 would be safe to run in this engine? I'll run it then. What about adding some MMO to the gasoline? or is that not necessary?

i'll also probably be replacing my spark plugs to copper plugs as stated before, especially since when i pulled plug #6, there was no gap, all black carbon built up between the gap. So #6 may have not been firing for a while.

 

Yes, Delo 15w-40 is a fine choice as is Rotella.

Both are high in ZDDP, around 1300ppm. Also high in detergent. I don't know if your 300 takes 5 or 6 quarts, but whatever the amount, just substitute 1 quart with MMO.

 

Quick question though, what about a Leak down test in this situation? Would it be worth it?

 

Did you have somebody hold the throttle wide open while you did the compression tests? Your numbers are kind of low, but even, which is good. The leakdown test might well find something; you know about listening for air leaks at various points (crankcase breather, exhaust, cooling system, etc.), I take it. But I like Timbersteel's idea of making sure every part of the crankcase breather system (air filter, supply hose, vacuum line, (the PCV valve is new) is free and clear. Then try taking off the vacuum line and valve, and running an output hose into a can and see if it gets a bunch of oil in it.

The part that gets me is the oil blowing around the sparkplugs. How? Unless the plugs were already loose, they normally should hold so much pressure that you'd hydraulically split a cylinder wall or something before the plugs would fail. And where did that quart of oil go? I do know that with enough blowby you can start blowing oil out of the crankcase (my overflow test, above). But if the PCV system was unobstructed, that much blowby should put so much oil into the cylinders, I'd think you'd see considerable white smoke out the exhaust.

 

I forgot to leave the throttle open when doing the compression test, the engine also was cold from sitting, my first time, I'll probably go back and try again.

I just bought it a pvc valve a week or so ago, but I'll check the vaccum lines running to it. The blow by on the valve cover is spewing out of the valve cover breather grommet, and leaking onto the hot metal of the cover, and burning off.

The spark plugs are a bit of mystery to me too. While the tips of the plugs are dry and covered with carbon build up, , from the threads out, are what is wet. Is there any seal around that portion of the spark plug in the head?

 

Good catch Seattle Smitty!!
I completely didn't think of asking about the throttle plates being held open for the compression test.

And also, I bought a jug of Delo last night. It's around $11.32 not $13.99 as I thought it was. That's $2.83 a quart!

 

Those are taper-seat 18mm plugs, IIRC. If the threads aren't stripped and the tapered seat in the head isn't dinged, when those plugs are torqued down, nothing should get by them. Have you ever tried to break up the ceramic of a spark plug with a hammer? I've occasionally done this when I wanted to make a special tool using the metal body of a spark plug. That ceramic is very tough; the only thing that will break a spark plug in a running engine is detonation.

Try your compression test cold again, but with the throttle open. Then squirt a fair amount (I don't know, maybe a teaspoon-worth) of engine oil into each spark plug hole as you re-test each cylinder. If adding the oil causes the reading(s) to go up significantly, that means your ring-sealing was improved by the excess oil, therefore you very well might be getting blowby from worn rings. If the added oil causes a big improvement in one cylinder, it still might be a cracked piston.

 

I ran another compression test today, with the trottle open all the way, and this is what i got:

Cyl 1 150 psi
Cyl 2 155 psi
Cyl 3 155 psi
Cyl 4 150 psi
Cyl 5 150 psi
Cyl 6 155 psi

I also ran a wet test, but i realized afterwards i used too much oil. It's a wonder it fired back up at all. Where as everyone said teaspoon, i probably added a few tablespoons full. After i started the truck back up, it smoked so bad that i thought it was going to catch fire. It smoke a good 30 minutes after this until it went away. That was my mistake.

So the wet test probably isn't accurate as it should be, but all cylinders jumped up to 170-175 psi. I had a few go past this by a little, but like i said, i added to much oil.

If i had to guess, i wouldn't think it is the rings. What about you guys?

 

Those are definitely MUCH better numbers than your first test. ~150 all around is really decent compression.

And don't feel too bad, I made the same mistake the first time I used oil to check the rings. (glug glug). I was blowing smoke for a while. I made the foolish decision to go drive it off because it sure made everyone behind me pretty upset.

I wonder if you have other things going on like maybe some bad valve seals, or a bunch of crud in the oil passages. I'd try a really good cleaning and go from there.

 

I blew my first cylinders rings one day.
and I knew it immediately. I had a glistening oil change and above 2500 rpm in fourth gearbit spewed some serious oil out the breathers. I solved it by taking the front tube, and sticking it in the catch can I made( stabbed a hole in the carb cleaner can I had) and whenever I'd start to notice a haze behind me while driving, I'd pull over and dump the can of oil back in(i had a spare being built) I went close to ten thousand miles like that and no issue when I pulled it. Never bothered changing the first cylinder spark plug. It was always just straight oil.

 

Wait a minute, you said you did a "wet test," which I guess means you put some oil down the spark plug holes. But the idea was to turn the engine over a few turns, to get the oil spread around, and then to RE-test compression (having FIRST checked compression WITHOUT any added oil)(but with the throttle open in all cases). If compression goes up a bunch on the second of the two tests, that means you have worn rings, which the excess oil is temporarily sealing, giving you a boost in compression. Didn't you do that test? That was the point of adding the oil, to do that test.

But anyway, if you are getting 150-155psi WITHOUT the added oil, your rings would seem to be okay.

What is going on here?