I'm working on an 87 Samurai with the stock engine that smokes a lot after warming up.  The smoke doesn't really have an oil or antifreeze smell and is grayish white.  A compression test shows 150 psi on all cylinders and it doesn't seem to be losing coolant. Plugs look like it's running a little rich, but not bad.  Does not overheat and no evidence of water in oil.  I recently put on a rebuilt carb, but it starts and idles with no problems so I don't think that is an issue.  Any ideas on where else to look?

What mileage is on this engine ?
Also it might be the gas your are buying, Gas-a-hol? any type alcohol, when burned, water vapor is a byproduct.
If you live in a cold weather state, you will even see frost on the side of the vehicles were the exhaust pipe comes out.
 OR It might be oil passing at the valve stems.
When this gray smoke appears, leave your hand in the exhaust "Smoke" for a while,
Does it make your hand wet with water? Or have an oily feel in you fingers?
Now on a clean white rag, press your hand into it and leave it there for a bit, later check it for stains...
Oil, antifreeze, etc.
It isn't a scientific approach, but it old school.

CAPT

Thanks for the response.  The odometer says 59,000, but it could be 159000 also.  I'll try out your suggestions.
I don't think it's valve stem seals, since no smoke on start up.  When that be something that would start leaking as the engine warmed up?
It could be fuel, I did add some carb cleaner to the gas at more than the normal ratio trying to get some carb issues to correct themselves. The smoke doesn't really have a distinctive oil or anti-freeze smell like I've noticed with other older cars I've worked on.

Hello again,
I tried some block sealant today.  Instructions called for adding to cold engine then running at idle for 50 minutes to a hour. First time around, I pulled the thermostat per an instruction video on the vendor's website.  No apparent improvement and the coolant never got to operating temp.  Re-installed thermostat and tried again with marginally better results, but now I seem to have another problem. 
The muffler on this one is rusted through and what I thought was water dripping from the rusted out area was oil.  How would unburned oil wind up in the exhaust system?

Are you positive that its oil? Not just water mixed with carbon in the exhaust. I would think if its straight oil it would have fouled a sparkplug or plugs and would be running like crap.

Thanks for the response. Yes, it's oil, crankcase was just  a little under full when I started and a quart low after two hours of idling.  There are several things I can't figure out.  Plugs do look like it's running rich, but not oily.  It idled smoothly the whole time with temp gauge showing normal the whole time after I put the thermostat back in. 
Took advise of previous post and checked a rag for staining with no apparent antifreeze or oil from the exhaust showing up on the rag. The tailpipe smoke has a lot of water vapor with clear water dripping from tail pipe though it doesn't have the characteristic antifreeze smell and minimal if any coolant loss during the two hours of idling. 
Looking at the exhaust, I can see oil staining at the cat and joint for the extension pipe.  Oil dripping from a rusted out muffler at a low point.  I'm changing the PCV valve out tomorrow to see if that helps.  Problem now is that with the oil in the cat and muffler, I'm probably going to have smoke no matter what.
If the crankcase pressure was up due to bad PCV, would oil pushing through the exhaust valve seals make it to the tailpipe without burning?  Surely it would burn if it was coming from the intake valves.  Any ideas will be appreciated

I would make sure to double check your fuel air adjustment especially if you just put on a rebuilt carb and also check the timing.  I recently went through a similar episode with my girlfriends Sami, looked like smoke and I thought it would account for the loss of oil but it turns out that it had jumped time.  I am still in awe at how this engine was able to run at all albeit not really well as far out of time as it was.  I also saw plugs with severe evidence of being run rich (this actually went on for quite a while) and the loss of oil in my case was from the rear main.

I only mention these because I beat my head against a wall for way too long before I discovered my timing issue, the symptoms really didn't point me that way and I do see some similarities from your description.  It looks like you've nailed down your problem but having more information never hurts.

J.T.

Thanks for the advice. I think the carb is okay, but can't be sure since I'm not able to run any exhaust gas tests.  As far as timing, it idles smoothly, revs smoothly and will run out just fine except for the smoke. I've pretty much decided its a head or head gasket issue.  I'll check timing just to be sure.

I'm planning to fix this Samurai up for a daily driver and plan on keeping it for a long time.  Given the long range plans, I'm considering a rebuild of the engine or just purchasing rebuilt engine and starting fresh.  Any advice on pros and cons of rebuilding vs buying rebuilt would be appreciated.  If anyone has experience with some of the suppliers like Samurai Salvage, John's, Petroworks, etc. I'd love to see your comments.

Rebuilding your own engine is nice.  You know exactly what went into it and when something fails you can blame yourself.  But it is time consuming and never as cheap as you think when you get started.

Buying one is the opposite.  You know exactly how much it will cost and don't have to spend the time working on it to get everything together.  On the other hand, when something goes wrong your always annoyed because you expected someone to do a better job then you could for the amount you gave them.