Final answer:
Sodium and potassium in used oil analysis are indicators of a coolant leak, which can seriously compromise engine health.
Step-by-step explanation:
The two elements in used oil analysis that can flag a coolant leak are sodium (Na) and potassium (K). These elements are commonly present in engine coolant additives, and significant levels in oil can indicate that coolant is contaminating the oil. Detection of these elements is critical for maintaining engine health, as coolant in the oil can lead to increased wear, corrosion, and reduced lubrication efficiency. An oil analysis can also check for the presence of other substances such as glycol, which is a direct indicator of coolant presence.