It never happen before, but just recently, just when I switch the ignition to ON(switch to where all the warning lights come on, one step before cranking the starter)and after the car is started up, I can hear a "lololo" sound(sounds like someone water flashed down a pipe). What seems to be the problem??

P.S. 1992 400SE, 68700KM on the car.

Is the coolant tank full? Souns like air purging from the heater core.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Yes, the coolant tank is full. I have replaced water pump just before the sound started to happen, can it be the cause??

Regard.

'92 400SE

Air in coolant system just run the engine with heater on & coolant cap off this way coolant will push the air out.