'78 Bus - Trying To Identify Source of Humming Noise

locoqueso · Post by **locoqueso** » Sat Jul 11, 2009 4:03 pm

While at a stop light today, I noticed an odd noise as the bus idled. At first I thought, or at least hoped, it was from the power lines above. The light turned green and I drove away. I could not hear the noise as I was driving, but it was audible as soon as I stopped at the next light. I drove the bus home to find the source of the noise.

The noise kind of sounds like the humming of an electric motor. The best I can describe it is like listening to a gremlin vacuuming carpet in the next room. It is loud enough to hear at idle, but not over the engine while driving. At first, I thought it was the sink’s water pump, but it was not. I then thought it might be the fuel pump, but I don’t think it is that either. The noise goes away when the engine is turned off and it doesn’t start again until the engine is running.

With the engine running, I actually hear it best when I’m sitting on the rear bench, with my head leaning back over the engine compartment. I’m fairly certain it’s coming from somewhere in the rear of the bus. I couldn’t hear it as well when I went back to open the engine compartment door. I stuck my head in and thought it might be coming from the side, near the battery, but I couldn’t hear it loud enough to identify the source. If I had to bet money, I’d almost say it wasn’t coming from directly within the engine compartment, but that’s a tough call.

I wanted to record the noise, but I can't find my mic. Any suggestions or ideas on what it might be or what I should do to identify the source?

IFBwax · Post by **IFBwax** » Sat Jul 11, 2009 4:41 pm

It sounds exactly like your fan blower, but you'd know that right?

locoqueso · Post by **locoqueso** » Sat Jul 11, 2009 5:10 pm

You'd think I'd know, but I'm not sure. I went back and double checked and it "could" be the fan, but I still can't say for sure. I guess my hearing is shot from that damn rock n' roll music. I always have a ringing in my ears.

With the engine access lid closed, it does sound like it's coming from the engine compartment. As soon as i open it up, the engine noise is too loud for me to pinpoint the humming. I even tried a short piece of hose to hold up to my ear. I got right up on top of the fan and I still couldn't tell for sure, but that does seem promising.

I should check my Bentley, but is there any harm disconnecting the wires and/or fuse to the fan to see if that kills the noise? I can get back out there tomorrow morning for a fresh look.

Randy in Maine · Post by **Randy in Maine** » Sat Jul 11, 2009 5:31 pm

Could it be your electric fuel pump cavitating?

vwlover77 · Post by **vwlover77** » Sat Jul 11, 2009 5:41 pm

Easy way to tell whether it's the fan blower or not: If you turn the key to "on" but do not start the engine, do you hear the noise? If yes, it's the fan blower. The fuel pump won't run until you start the engine.

My guess is (unfortunately) a fuel pump straining against a clogged fuel filter or a restricted fuel line from the tank.

locoqueso · Post by **locoqueso** » Sat Jul 11, 2009 8:35 pm

vwlover77 wrote:Easy way to tell whether it's the fan blower or not: If you turn the key to "on" but do not start the engine, do you hear the noise? If yes, it's the fan blower. The fuel pump won't run until you start the engine.

My guess is (unfortunately) a fuel pump straining against a clogged fuel filter or a restricted fuel line from the tank.

No, I tried turning the key without starting the motor and didn't hear the noise. I only hear the noise with the engine running.

I have a brand new fuel pump, fuel filter, and fuel lines. I replaced all of them while Colin was here last month. Initially I did think it could be the fuel pump, just because of the sound, but I got down by the pump and I couldn't hear the noise. I'll crawl under the bus to double check the pump in the morning.

Post by **Amskeptic** » Sat Jul 11, 2009 11:12 pm

locoqueso wrote: Any suggestions or ideas on what it might be or what I should do to identify the source?

Spray belt with WD-40. Noise gone? Just the belt. Take off the alternator belt and run the engine. Noise gone? Sometimes the alternator brushes get noisy at the end of their lives. Distributor hot? Rotor grinding in the cap because it is not seated.
Colin

locoqueso · Post by **locoqueso** » Sun Jul 12, 2009 7:46 am

Amskeptic wrote:Spray belt with WD-40. Noise gone?...

Yes, that seems to have worked. I sprayed the belt with WD-40 and I no longer hear the noise, even with the engine compartment closed. I can't take it for a test drive yet, I also noticed my muffler strap is broken. It must have snapped yesterday. I'm going to order a new strap today and hopefully I will then be able to get back on the road next weekend.

Thank you and everyone else that responded!

P.S. I don't know if I would have ever guessed it was the belt. The noise wasn't the squeaky sound I would normally associate with a belt.

Post by **Amskeptic** » Thu Nov 05, 2009 9:40 pm

locoqueso wrote:P.S. I don't know if I would have ever guessed it was the belt. The noise wasn't the squeaky sound I would normally associate with a belt.

(Duroc, I split the topic here and moved the story to General under "That Noise")

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'78 Bus - Trying To Identify Source of Humming Noise

'78 Bus - Trying To Identify Source of Humming Noise

Re: '78 Bus - Trying To Identify Source of Humming Noise

Re: '78 Bus - Trying To Identify Source of Humming Noise

Re: '78 Bus - Trying To Identify Source of Humming Noise