An electric pump buzz which seems to be pumping the coolant continues for about 5min after the ignition is switched off on my wifes ML320 (1999).

Is this normal and if so why does it run after the engine stops?

 

That's the auxiliary electric water pump. It provides consistent engine temperature control during warmup and after engine shut down. It basically helps to maintain the coolant's temperature throughout the system, and not allow "hot spots" or "cold spots".

 

Thanks. Is there data that shows this increases engine longevity?

 

I'm sure there is data somewhere in Germany that proves the auxiliary water pump's effectiveness.

 

You'll be driving your ML several years from today. Don't worry about engine longevity. And, BTW, that fan lasts for 10 minutes, exactly.

 

Love this. Changed spark plugs, boots,and coils today and finally noticed that same coolant pump running, so I looked it up on MB world.
2004 Ml350, 201K miles. Runs like it will go forever.