Over half of the cores that we receive are cracked. Save yourself the wasted shipping cost or paying a machine shop when you can test your head yourself at home with this kit. Kit includes magnet, applicator and magnetic powder. Most cracks in 2.3 heads are found on the #2 and #3 exhaust seats in the area shown in the picture above. If you have a small crack, sometimes these can be fully machined out, please send us a picture and we can tell you if the head is salvageable before shipping. Another good area to test in addition to all exhaust seats is the cam towers. These heads can also rarely crack on the intake seats, so test the entire combustion chamber to be sure. ALL OIL must be removed from an area before testing however carbon is ok- it actually helps to show cracks. Enough powder is included to test multiple cylinder heads.