Subject: engine problems
Question:

I HAVE A 1999 MIT. MONTERO SPORT WITH AUTO V6.HERES MY QUESTION. ENGINE LIGHT CAME ON, TOOK TO SHOP, CODE WAS CYL. MISFIRE, MECHANIC SAID TUNE UP SHOULD FIX IT, AFTER TUNE UP FINISHED MECHANIC SAID WHITE SMOKE OUT OF TAIL PIPE AND HEAD GASKET WAS CRACKED. IS IT WORTH PAYING 800.00 FOR GASKET REPAIR AND 400.00 FOR TUNE UP OR IS THIS VECHICLE GOING TO GET WORSE? HOW LONG CAN I GO WITH CRACKED GASKET? 

Answer: Mario,
A cracked head gasket can be very serious. That white smoke is most likely coolant which is leaking into the combustion chamber, and burning off. Depending on how severe the crack is and how much coolant is seeping past, your coolant level can go down quickly. If you were to run out of coolant while driving, your engine would overheat and completely destroy your engine. There's no telling how long the cracked head gasket may last.

If your Montero is in good condition other than the bad head gasket, it is still worth anywhere from $7000 - $12,000. So, spending $1200 for a head gasket and tune-up may be worth it to you.
Good luck!