No Start in Cold Temperatures
 

My father in law has a 1991 300E that simply won't start in cold weather. The starter turns but the engine will not turn over. The problem has existed for some time and the car has been serviced numerous times. The only way it starts is if we hang a light bulb in the engine compartment overnight. This apparently keeps it warm enough to start normally the next morning.

Bad sensor?
Any help/info would be appreciated.

Thanks,
-Jeff

Possibly the solder is cracked on the fuel relay board. Temperature may cause expansion or contraction to the board thus allowing intermitant contact.

Solution is to resolder the cracked pin connection... or replace fuel relay with new one.

To inspect... remove relay... then pop off cover... inspect solder pins (on the printed circuit board) of circuits that run to pins 7 and 8 of the male plug in. If you see a crack surrounding the pin... solder it or replace relay.

Alternatively listen to see if fuel pump is buzzing when ignition is first turned on. If not then problem is most likely with the relay.