When the engine is running, what is a sign that the oil is circulating properly?

When the engine is running, a sign that the oil is circulating properly is indicated when the warning light goes off. This warning light is designed to alert the driver when there are issues with the oil system, such as low oil pressure or low oil levels. When the light goes off, it suggests that the oil is circulating appropriately, with sufficient pressure and volume to lubricate the engine components effectively. This is crucial for maintaining engine health and preventing overheating or damage due to inadequate lubrication.

The other options do not properly indicate good oil circulation. A steady oil temperature gauge could suggest that the engine is running smoothly but does not necessarily confirm that the oil is circulating. A decreasing oil pressure gauge reading is alarming and indicates that there may be a problem with the oil system, signaling potential low pressure that could cause damage. Additionally, seeing an increase in oil level on the dipstick is not a sign of circulation; it could indicate an overfilling issue or contamination with fuel or coolant, which are problematic. Thus, the most direct sign of proper oil circulation in a functioning engine is indeed when the warning light goes off.