can anyone explain this?
 

i have 4 mb diesels on the road.it was 5 degrees this morning.my 79sd has no block heater yet fires rite up.84 sd was not plugged in and did not start ,87 300d no heater fires rite up.87 sdl no heater car covered with snow and ice not run in weeks fires up.why does the 84 not start.glow plugs new bosch,, timer is new..cranks fast.car runs great.plug in bloc heater for 2 hours and it kiks rite off.175000 miles....tomorrow it will be below zero ill plugg it in and it willl fire rite up.i gotta know why........

Adjust the valves and change the fuel filter.

My '82 started up this morning but then gave me grief when the fuel started to gel while I traveled down the highway. It was -15 here in Central Illinois. I filled the tank the rest of the way and the problem was solved by the addition of warmer fuel.

Since you pluged it in and it started takes away any fuel leak problems. Mine had bad O-rings on the injector pump to the lines and would let the fuel return to the tank. specially if the nose of the car was up hilland fuel below 1/2 a tank. You had to crank the heck out of it to get the fuel back do to manual fuel pump. If you change your fuel filter warm the car and fill the filter up with a injector cleaner and start it. Also check the resistence of your glow plugs to insure their all good

check to make sure the glow plugs are workin (check fuses) and put some anti gelling stuff in the tank