Merc 5.7 1998 Hmmm.... Sound

[victoryinerie]

I just bought a new boat and picked it up last night for me it is a 1998 Larson Hampton. I am doing all the normal checks before I take it to the water and everything seem fine, however I noticed a slight Hmmm noise from the engine area when the battery is on(engine not running), if I shut the batteries off the sound goes away. Any thoughts on what this might be? It does not stop after a period of time, I charged the batteries throught the nite and when I woke up this morning the sounds was still there...

 

[Don S]

Re: Merc 5.7 1998 Hmmm.... Sound

Get back there and follow the sound till you find out where it's coming from.

 

[Utahboatnut]

Re: Merc 5.7 1998 Hmmm.... Sound

Is the bilge pump staying on somehow (switch in manual/bad float switch) if mine is on and the engine is not running I can hear a hum back near the batteries.

 

[Danny Mc]

Re: Merc 5.7 1998 Hmmm.... Sound

I find trash holding the float switch open more than bad switches, easy to check, if float arm is down and ign is off and bilge pump is running it's prolly bad switch, "if" it's wired correctly.

 

[franktrav]

Re: Merc 5.7 1998 Hmmm.... Sound

automatic bilge should operate with or without key in the run position,this is how it pumps water from an un-attended boat left in the water. ive had my float switch jammed with debris and it made the same noise you describe.
also, an electric fuel pump that fails to kick off when the pressure is correct would also make the sound you describe...and that would be a key in run position only issue