Do I Need a Torque Wrench?

If you plan to do any major work on your engine or on some major powertrain components, you absolutely need a torque wrench. Overtightening cylinder-head bolts, for instance, can easily cause expensive damage and catastrophic coolant loss. Too-tight exhaust manifold bolts can cause the manifold to crack.

What happens if you dont use a torque wrench?

Too tight and something will break, it may be the thread on the bolt, or much worse the thread on in the hole. Bolts will also break, sometimes leaving a very hard to remove bit in your frame.

Do you need torque wrench for lug nuts?

Yes, when possible use a torque wrench for wheel nuts and bolts. It's not safe to under tighten a nut/bolt and it may be damaging to over tighten (or you can't loosen it later). Also you can/need to retighten wheel nuts and bolts after a short time to check if they remain tight after the initial tightening.