i replaced the plug on my heater cord, plugged in Sat nite and when i got up sunday to go to church the engine was cold.

1. does the cord go bad while the heater is good?

2. should they be replaced in tandem like shocks?

Sounds like your block heater may have givenup the ghost. But before you dispare, make sure you have power on the extension cord you ran. Could be as simple as a popped breaker or switched outlet you were plugged into, or a socket that went bad.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

i should have mentioned that i have checked and tested successfully

1. the outlet lit up a bulb
2. the screw in adapter and 3 prong plug adapter worked in the house lamp
3. the outdoor cord was connected to and ran the table saw

I replaced a badly taped plug from the po. so i am still looking at the cord or heater. but with the other ideas hear maybe i don't need it.

whats the opinion here between block heaters and the hot water heaters?

I would unscrew the cord from the block heater and check it out. If it tests good buy just that part.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

take off the air cleaner and clean the oily residue from it and then remove the intake manifold and clean it and while it sits attack the block heater.

yeah i do read the forum pretty indepth. will advise.