Detroit Diesel coolant temperature range.

• A. 180-200
• B. 160-180
• C. 200-220
• D. 180-220

Answer: (D)

The coolant should be kept within a window that covers both warming up and staying safely hot during operation. About 180°F is the point at which the engine reaches efficient combustion and proper lubrication, while up to around 220°F stays within the normal safe operating limit for most Detroit Diesel engines. If the temperature stays too cold (below 180°F), you’ll see poorer fuel economy, higher emissions, and increased engine wear because the engine hasn’t reached its optimal operating temperature. If it climbs above 220°F, you risk overheating, which can lead to coolant loss, warped components, and gasket damage. The range that spans roughly 180 to 220°F accommodates both getting the engine up to temperature quickly and keeping it within a safe operating limit under typical loads, making it the best choice.