Water jacket:

Water-cooled engines could overheat if the cooling water system fails to remove waste heat. Removal of the waste heat prevents the engine from seizing due to excessive expansion of the components under a high temperature condition. A cooling water jacket is commonly where the sensor for the cooling water system is situated.

The water jacket temperature sensors give early warning of abnormal engine temperature, commonly an alarm function only. The setpoint is set such which if the condition is corrected in a timely manner, important engine damage will be prevented. But continued engine operation at the alarm temperature or higher temperatures will lead to engine damage.

Exhaust temperatures - Within a diesel engine, exhaust temperatures are extremely important and could give a vast amount of information regarding the operation of the engine. High exhaust temperature could denote an overloading of the engine or possible poor performance because of inadequate scavenging (the cooling effect) in the engine. Extended operation along with high exhaust temperatures could result in damage to the exhaust piston, valves, and cylinders. The exhaust temperature commonly gives just an alarm function.