smd

Hi,

I bought a 1992 300 SL 24 a few weeks ago. I really enjoy driving in it. When the engine is on I keep hearing a humming sound coming from behind the front seats. Now I know the engine is in front so does anybody have an idea what this could be?

Thanks.

LeaUK

There are two pumps in the rear, one for hydraulic fluid and one for vacuum - could be one of these.

Lea

smd

Thanks, someone told me that it could also be the fuel pump as it is apparently located there as well. Are you supposed to hear this humming sound or do you think I should get it checked? In stationary position it is quite audible!

grege

Yes fuel pump is rear right wheel well area, just behind the driver in a RHD car. Mine makes a bit of noise (done 120ks), will get it changed at some stage but has been that way for a while, not seen any problems from it yet.
Greg E

LeaUK

If this sound is continuous then I would also suspect the fuel pump. My '93 is silent whilst running and the fuel pump can only be heard just after I turn the ignition switch on and before I start. I tend to leave the car in this position for two to three seconds just before before I crank to ensure stability - but that's just me.

Get it checked as it shouldn't be noisy!


Lea

500SLZ

Okay, so I have the same sound when the car is running... so, if I turn the key to the running position (without starting) and I hear that same humming, then the noise would be the fuel pump. If I don't hear any sound, it must be something other than the fuel pump... what else could be a motorized humming that seems to originate behind the rear wall that is continuous when the car is running?

SRHsl600

With the key in, but no engine turn, the fuel pump is audible in my 94 SL600. With the engine in low RPM, but not in motion I can still hear fuel pump, vacuum and hydraulic pumps. When driving all those sounds are muted relative to radio, wife, wind and road sounds. In all my vehicles I have waited for pump failure!

500SLZ

LOL! Thanks SRH, I catch your drift! Now all I have left to do is figure out how to unlock the inside of the car and I'm good to go!

SRHsl600

Key slot above vent, ( center of the car ) is where the door pockets, interior back deck door and console compartments can be locked as a guard from pilfering when the vehicle is topless

500SLZ

Thanks for the reply SRH, I've got that one figured out now, I'm dealing with the ol' Central Locking System virus! From what I've read during last week since purchasing my first 500SL, is this affects one hell of lot of folks out there with SLs. My pump is brand new and crating vacuum, but won't unlock the interior compartments. It runs on too long as well, giving me the idea that there is a broken or disconnected line somewhere. Where and how to access the problem is a nightmare for me as I'm not familiar with the 500SL. This has made for hours of fun in my garage trying to figure out where there is a leak or malfunction as I need to get into the rear storage compartment to fix the blown subwoofer!

SRHsl600

yellow tubing is tough, but connectors can come apart. center console, door panels and radio space is where I would listen first. If those panels or access ports have been open , it is easy to not connect when they are replaced. Good luck on the hunt!