White smoke out of your 97 montero 6 cylindr sports utility truck?
Common Montero problem. I'll bet you're burning oil - do you find it is a quart low every 4,000 miles or so? Get your favorite mechanic to do a compression blow-down test - I'll bet you need rings. Oil is seeping into your cylinders. You can drive the truck like this for a long time without really having a problem - just make sure you keep checking your engine oil level. If your state does emission checks, you're going to fail.
If you get the rings done, you'd do well to complete an engine rebuild while you're at it; the motor's already wide open, so you're going to see significant savings on labor.