Let me give you the short story.
About a week ago, I did an oil change on my 2000 Z24 with the 2.4 Twin Cam engine.  Castrol Syntec Blend 5W30, and ~1 Qt Lucas Oil stabilizer, to what [I thought was about a total of] 4.5 Qt.  I've been using a little Lucas for the past many oil changes, no problem, and I use it religiously in my '89 Z24.  Anyway, I head to work.  22 Mile drive.  Towards the end of the drive, I ran around 5000 RPM for around 30-40 seconds (Going up fairly steep hill, for a 4 lane highway, accelerating).  I pull off the offramp, smell a little something weird.  Pull into the parking lot, and smoke's coming up out of the hood.  Doesn't smell good.  I check my oil later and I'm at the "add 1 qt line".  Don't have any oil, so I drive it real light on the way home.  I pull into the driveway, smoke is minimal (but remember I drove it lightly).  I get home, and I add 1qt of Castrol Syntec Full synthetic.
Tuesday, I go out, drain the oil and change the filter, thinking maybe I got a bad filter or something, which has never happened before. While underneath the car, I notice that oil seems to be all over, and seems to be originating from the rear, lower-middle portion of the motor (nowhere near the filter), up too far in a cranny to really pinpoint, I just know that there is more oil on the lower rear of the motor and tranny pan than I am used to seeing.  I wiped everything clean, so I could tell if it gets covered again.  Anyway, I reuse the oil since it is still clean, (refilling it with a straining funnel) and fill it to the top of the Full range.  I drive it lightly to work and back (44 more miles round trip), still smell the smoke, but only actually see minimal smoke.  I checked the oil level and it seems to be in operating range, but it's so dark I can't even tell, since the oil is still so clean.
After all that's happened, the car still starts easy, and seems to run fine.  Only thing I notice is that the motor seems a little warmer when I come to a stop than I think it should be, though I haven't really paid much attention to it before.  I am not overheating, according to my temp gauge.
I will be pulling it up on ramps on Wednesday to see if  I am still leaking.  I really hope not.  Has anything like this happened to anyone with a 2.4 Twin cam?  This motor has 54000 miles on it, and the only modding I have done thus far is MSD Ignition, and a short ram warm air intake. 
Somebody please tell me you know what I should do?!!  Thanks in advance 1000x!~!!!  I care much for the car, and don't want it to DIE!
--==pghcavman==--
 
Oh yeah, forgot to mention that I checked my coolant, to see if somehow I blew a head gasket.  Coolant's 100% clean.  If it's a gasket, it's external leakage only. 
BTW, I haven't taken apart a DOHC motor yet.  I've taken heads off of, and put back together both a 2.2 I4 OHV and 2.8 V6, but no OHC motors yet. 
What could have happened here?
--==pghcavman==--
 
Most likely its just an oil seal somewhere.  Probably the crankshaft seal.  If you have a hayns manual or another repair manual look in there to see how to change the engine seals.  If your not comfortable with that just take it to a mechanic.  Unfortunately it is expensive to have a mechanic do it where as the part itself is pretty cheap.
 
Well, I just got home from work about an hour ago, and no signs of smoke.  I will be checking my fluid levels tomorrow and see what I see. 
--==pghcavman==--
 
It's been about a week.  No more sign of smoke, and running fine.  
--==pghcavman==--
 
that lucas @!#$ sucks. dont use it.
running at 5 k for like 40 secs probably just made your engine extremely hot, which had something to do with metal expaning and oil going where it wasnt. idk if that made sense.
-Borsty
 
aint nothing wrong with lucas, its a proven product and it works!
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** Flat Broke Racing Inc.**