Strange noise. Not sure where to post this?

[john rh]

Hi,

After some help again!

My 1986 500SEL has a strange noise in the interior that I can't identify or track down:

- High-pitched buzz, similar sound to interference on a radio, but at a higher pitch and constant - it does not change with engine speed or road speed
- Not a loud noise, but enough to be annying
- There is no noise when the car is started from cold, it comes on after the engine has run for about 5 minutes then stays until the car is switched off
- Happens whether electrical fittings (e,g, radio, fan) are switched on or off
- Seems to be coming from the front left of the interior, I think?

Any ideas or tips much appreciated!

John

 

[Superspec]

Could it be the nearside thermostat? That would be affected once the engine is up to temperature. I assume you have separate temperature controls on each side of the car? Do you have any temp control issues?

 

[donubenz]

Hi,
Just a suggestion and may be worth a look.
I had a 126 S class with a strange noise from the dash. Mercedes had in their wisdom fitted a small fan unit (about 35mm diam 60mm long) to blow air from the cabin across the heat sensor for the air con. Apparently when the car is in hot sunlight it fools the sensor and blows cold air continuously. They were rubber mounted but as they ran all the time the motors became noisy. Most garages just disconnected the plug to isolate the fan as the effect does not happen much in the UK!
Don

Part number is Bosch 0130002806
one for sale in US ebay with pics
http://cgi.ebay.com/ebaymotors/BOSCH-APK-12V-0130002806-FAN-MOTOR-/150557733361

 

[stwat]

It sounds to me like it's the little electric pump that draws in air from the cars interior through the small vent next to the interior light to monitor the interior temperature. Its so the heater can monitor and regulate temp set by the heater controls. The system is fitted to non A/C models as well as A/C equipped cars.

The pump sits where you describe. It sounds like your motor is on it's way out.

Beaten to it by Don

 

[john rh]

Could it be the nearside thermostat? That would be affected once the engine is up to temperature. I assume you have separate temperature controls on each side of the car? Do you have any temp control issues?

Temp control seems OK, I think, but it's worth checking. Where do I look for the thermostat?

Thanks

John