3406, 3408 Truck Engines
Operation of 3406 and 3408 Truck Engines at below normal engine temperatures can cause increased fuel consumption and increased engine component wear.
Engine operation at temperatures below 71°C (160°F) is usually found when heater performance is not correct and/or the temperature gauge indication is low.
Check the engine operation temperatures with a gauge of known accuracy. This will give a check of the truck's engine temperature gauge.
The main cause of low engine temperatures is the flow of coolant past the water temperature regulators at a temperature below 71 °C (160°F). Identification of the leakage circuit is necessary to corect the problem. To do this, check:
1. Operation of the water temperature regulator.
2. Make sure the correct regulator cover assembly is used. Use of the wrong cover assembly can cause low engine temperatures. See the March 12, 1980 ENGINE NEWS article, "Inspect Regulator Cover Assembly When Overcooling Is A Problem. "
If the water temperature regulator works correctly and the correct regulator cover assembly is used, an 8N9071 Valve Assembly can be installed in the air vent line. The air vent line, which goes from the cylinder head to the radiator, is used to remove air from the engine cooling system. Without the check valve, it is possible for coolant to flow through the air vent line when the water temperature regulator is closed. The check valve prevents this coolant flow.