PeachParts Mercedes-Benz Forum - View Single Post - Is it safe for the engine to turn off the recirculating pump?

pcmaher · #8 02-04-2008, 02:07 PM

In addition to providing hot coolant for correct heater operation, the auxilliary pump is also meant to assist engine cooldown. See following text taken from MB literature. If your engine sees high temps, you could be risking damage. See the Engine OFF Cooling section in particular...

PURPOSE
The coolant circulation pump is arranged in the return circuit to provide constant coolant flow through the heat exchanger during heating operations.

OPERATION
When a heating function is selected, the climate control unit energizes the coolant circulation pump continuously. When the control unit determines that heating is no longer required the pump is switched of.

Engine OFF Cooling :

At engine coolant temperatures greater than 100 °C, the coolant temperature is monitored for 90 seconds after switching off the ignition.
If the coolant temperature exceeds 110 °C after 90 seconds, the coolant circulation pump (A3lml) is switched on for a maximum of 10 minutes to assist in cooling the engine. Should the coolant temperature drop below 110 °C during the 10 minute period, engine OFF cooling switches off.
During engine OFF cooling:
Coolant circulation pump (A31m1) is ON,
Coolant pump control relay (K30) is energized,
Blower motor (A32m1) is OFF,
Left and right duovalves (A31y1, A31y2) are closed, thereby opening the bypass for engine OFF cooling.