Heat Tabs are small metal tabs that contain a specialized material in the center designed to melt at a specific temperature. They are used for monitoring engine temperature to determine whether or not a motor has exceeded the recommended margin, otherwise known as "overheating."
These are Diesel heat tabs and they melt at 255-260 F
(need a lower temp tab, try 411-5811-90)
When you attach a heat tab to the engine it provides visual evidence that an engine has been overheated. A special heat sensitive metal has been formed into the center of the tab. When an engine reaches the tab's melting point, this metal will melt and flow out. This is a positive method of determining that a rebuilt engine has been heated beyond normal operating temperature, voiding the warranty. Attach a Heat Tab to the upper portion of the block or to the cylinder head casting with Aluminum Paste (411-5811-82). DO NOT attach to manifolds or shielding.