94 E320 black (sensor)? wire hanging from middle of front bumper?
 

I have overheating in the engine and found a dangling black wire nwith a bulb sensor at the end with an eyelet for a bolt hook up to something. Any idea where it's length of wire should attach?
Of course I also noticed a bubling sound in the firewall heater hose. I added two quarts of water to the low overflow container and radiator lite went out until it heated up again pretty rapidly. Looking at the t-stat I jiggled the black hose going to the right middle side of the radiator and noticed the silver tightener was leaking. Nice if that was the problem, does it sound like t-stat replacement time?
Thank you

I believe you are describing the Ambient Air Temperature Sensor

Ambient air temp msensor location
 

Thank you for that info. Does it attach at any specific location or attached in the air stream adequate ?

thermostat removal of system air
 

Can I get help on reoving air in the system when the T-stat is replaced. A comment was made to be carefull of this but do not know how?
Thank you

sensor attachment
 

It attaches to a round plug-in, if I remember correctly it's on the inside of the lower right side bumper, but you will see if if you look carefully. it just plugs in, probably just fell out. (measures the outside air temp indicated on your dash)

I'm no expert but things I've learned from this site is that MB thermostats are designed to fail open. So an engine overheating because of a Tstat is unlikely. Sounds like you're losing coolant. Could be the head gasket - same engine as my wagon - and the original ones are bad. Check your hoses too. The top hose to the radiator can wiggle loose and the neck on those can crack too. How many miles on the car?

Check Water Pump
 

On my E320 1994 the water pump was leaking massively. I put water in one day and the next it ran nearly dry and overheated. THEN the head gasket went. So check the water pump.

On my 300CD, the upper radiator hose was leaking coolant. It had the original MB clamp on it. I tightened it a lot but it still leaked. My mechanic gave me a bigger no brand one to try and it solved the problem.

Worth trying?