Opinions are like buttholes, everybody has one, and they all stink...
We are just making guesses here....
Butt....
I have to agree with the 'Dawg' here...
It sounds like water getting into the engine somewhere...
And never, ever settle for Knurling in valve guides. Knurling is for freshening up an old, tired engine a little, not for a fresh rebuild.
Get new guides, and have them HONED to size. Never let them use cutters or knurling tools on valve guides for a fresh engine.
The three angle valve job probably isn't necessary for a mostly stock six cylinder, but it won't hurt anything either. Neither will cleaning up the head ports or matching the intake to the head(s)...
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You said the Jeep sat in freezing weather for a period of time...
Did it have adequate antifreeze during that time, or do you know?
It sounds like the block may be cracked internally if there wasn't adequate antifreeze.
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Anytime you get the gray sludge you described, there is water in the oil, or you have mixed oils that shouldn't have been...
If it were me, I'd tear the engine down, and inspect all of the gaskets very closely for a leak. (tear down inspection is a lost art)
I'd have the block and heads pressure tested for leaks.
If they pass, I'd pay to have the block and heads inspected for cracks, either with ultra sound, chemical inspection, or magnetic inspection.
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Some things you might try...
1. Leave the vehicle sit overnight, crack the drain plug in the morning and put a glass jar under it. Don't take it out, just crack it loose about a turn.
Allow the jar to get an inch or so of the contents of the oil pan in it.
If you get water in the jar, DON'T run the vehicle until you change the oil, then take it to a good shop for further tests to tell the location and extent of the damage.
IF you don't get water or antifreeze, that doesn't mean there isn't a problem, it just means you have to look a little closer...
2. Keep a pretty healthy sample of your used oil in a clean container, preferably glass...
Have someone with a air conditioner leak detector 'Sniff' the sample.
(whip out your chemistry books folks...)
Modern antifreeze has ingredients that release halogen gasses.
Air conditioner coolants also contain halogens, and the leak detector will detect the antifreeze in the oil, even in small quantities...
We sniff the dipstick tube before we buy cars now just to tell if the water seals in the engine are still intact.
(It just tickles me to the core to see some ASE guy trying to do freon leak detection on a vehicle that has antifreeze leaks... he has to turn his sensitivity down so far the detector is useless, but he can't figure out why the job keeps coming back...)
3. If you know someone with emissions testing equipment, you can look for exhaust gasses in the radiator when the vehicle is running. If the head gasket is leaking, during the compression and power stroke, raw fuel (unburned hydrocarbons) and exhaust gasses could be forced into the cooling system.
4. Do a pressure test on the cooling system.
Remove the water from the system, install a pressure test cap on the radiator, and add pressure.
If the pressure escapes, over time, there is a leak in the system.
It may be head gasket or the intake manifold gaskets...
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Just thinking out loud...
Good luck in your search, Aaron.
"I Have The Body Of A God... Buddha"