It all depends. Upon start up and warm up, you may see a little somke from the vent tube and it is no big deal if you do (or don't). Once it is up to operating temperature, it should not really smoke from the vent tube. Being that it is a used peice of equipment (you do not know the history of it) I would not be too worried about it unless it is vast amounts. If it is enought to keep the mosquitos off of you when running the tractor, it is too much. I agree with the previous post, if you have an issue with the dip stick popping out, then there is an issue. Also, at least at first, you may want to check the oil on a regulare basis and be sure that it is not "making oil". This means that diesel is running down the cylinder walls and filling up the cankcase (there are several causes of this). If it ain't dump'in diesel in the crankcase and the dipstick stays in, run it as long as you can. To be honest, if there is a small issue with the cylinder walls from some past "accidnet", you are not going to make it much worse by using the tractor. Just keep good oil in it, clean air filter, and keep the radiator clean. You may also want to watch your exhaust pipe. If the exhaust is clean or normal (not a lot of smoke) then I really would not be concerned. Just my opinion, hope it helps.