I just picked up my new to me 99 XJ that I bought from a forum member in NC who overheated it. My dad lives down there and his shop put a used motor with 100K on it that he heard run before buying and putting it in mine. Well he drove it around after the install for a week about 150-200 miles and only had one issue happen once for about a mile where it started to smoke a little more then normal out the exhaust but he shut it down, and started it back up and it was fine. Well I finally got it transported up here and it started smoking after about 5 miles of driving.. No loss of power, all gauges are reading good, all fluids are good, idle is fine, no misfire or sputtering or any unusual noises at all..
Also when the motor was put in all new gaskets/seals (except head gasket), thermostat, hoses, belt, battery, plugs and wires etc. were put on.
Any ideas what it could be?
Someone suggested it could be a sticky lifter?
It does have an aftermarket cat-back system that splits to duels after the muffler but I don't think that would make a difference..
I do have a video of what kind of smoke I am talking about once I have a computer near.
Any advice would be greatly appreciated!

I never heard of a lifter making a vehicle burn oil. It could be worn out valve seals or piston rings.

Make sure all the PCV hoses are hooked up right.. sounds like it might be sucking oil up from someplace.. Pull the spark plugs.. are they clean ?
A cloged or improperly hooked up PCV system can cause what you are talking about...engine case is not breathing right.. forces oil out through a Hose on valvecover to intake and it smokes...Or forces it out valve stem seals into combustion chamber ^ like he was saying

My 94 with 140,000 has been doing this for about 10,000 miles now.

This is exactly what i've read. In my case, it's probably the valve stem seals. I just haven't really gotten around to looking into it further.

White smoke = coolant

Blue or black smoke = oil

Keep tabs on the levels of both of these fluids.

Consider a compression test. Would have been a good idea before installing the engine. A good "snapshot in time" on the internal condition of the engine...........Easy to perform. Compression tester can be rented if you don't have one or don't want to purchase one. Check with a big box parts store.
The compression spec. is 120-150, with no more than a 30 psi variation between cylinders. A dry AND wet compression test would be best here...........

Mine is a slight blue-ish tint and CERTAINLY smells like oil. Smells/looks like a 2 stroke dirt bike on about 42:1 mix ratio.

It only does it out on the trail or when its been idling for about 7-10 minutes. You can romp on the gas from a stop light or whatever and it doesn't smoke a bit.

Steamy white is coolant and smells sweet blue black is oil you might have a warped head or when they did the valve job they mixed valves whats happening is when it gets hot whatever is the problem is expanding and allowing the fluid to pass

Sorry it took so long but here is the vid:


http://s93.photobucket.com/albums/l6...=VID_00021.mp4

Its whiteish smoke, and the coolant level didn't change on the 15-20 mile drive home..
Thats at an idle, after it has warmed up.

Does it smell like burning oil?

Not like burning, but it does have a little smell to it, not really sure how to describe it though..

And its not always there, which is whats the most confusing..
tomorrow when I have light again I will check it over more, check the PCV system and keep an eye on the fluids..

how cold is in OH? it looks like small amount of steam. could be water in the fuel.how long did it sit before the new motor?

Its actually pretty warm today say 40-45, and it probably sat for about a week before driving it (except on and off the trailer) and when I got it, it was about an 1/8 of a tank so I did fill it up.

As mentioned, want to make sure that it isn't the normal steam/water combustion process type of smoke here.

Hopefully this isn't a stupid question, but how does one go about checking that?

And thanks for all the ideas so far guys! Gives me a couple things to check here today.
And heres a quick pic of the new rig and the DD:


Edit:
I looked over a little bit (but not too much when its about 20 degrees and I don't have garage to fit this in..) I pulled a plug to see if it was fouled, but it looked pretty good all fluids still look good oil is still clean and full and coolant is right about where it was, and just checked over connections and such under the hood, and didn't find anything out of place other then the A/C compressor not plugged in, and the coolant overflow line looked like it was kinked between the cowl support and hood as if it was not routed right, so I moved that back and secured it back up.

What do you guys think of it having a stuck/bad injector? It makes sense in the fact thats not happening all the time, and everything else seems normal?
I have the fuel rail and injectors from the old motor and will just the whole rail in and see if anything changes!