My '90 Montero V6 has been emitting a good deal of smoke when started cold, seems worse in warm weather. It uses no coolant, and only about a quart of oil in 4 - 5K between changes. It is also intermittent. I think it may be worse in warmer weather. This smoke lasts a half minute or so and can be bad. Is this valve guides?

 

what color is the smoke?
if its a blue-ish smoke, its oil
ifs a white smoke, its coolant.
If its oil, it could be either the valve guides, head-gasket/gaskets, or just plain pooley seating valves.
if its coolant, it could be a bad headgasket (most likely), or it could be a bad gasket on the intake manifold.

BTW, there is a whole forum on here for the montero, and they may have some better answers for you there.

Also, you say that it gets worse when it is warm? could be a poorly functioning EGR valve. or even a bad pcv valve.
You really need to start your diagnoses with a good oil, and filter change, chaning of the PCV valve, and air filter, and also, consider a good internal engine cleaner, something like sea-foam that will eat up the carbon built up in the motor.

 

valve seals are the cause of smokey startup 99% of the time.

 

amen to that.