There are two different cord designs.

My 85 300D has the round screw on type. But I swapped the engine some time back for an ~82 engines out of an SD. It has the rectangular socket.

The rectangular plug may fit into the round socket, but the reverse is not true. I found shop had cut part of round plug away and it sort of goes in, but soon falls out.

I need the rectangular plug. they are readily available in aftermarket, but I just have not got around to it.

Instead, I use a magnetic sump heater. It works fine. Has the advantage that if I forget it is plugged in, if self disconnects when I back out of garage

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Bump.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

My car's OE block heater can take the round connection, but I was cheap and got one with the square plug instead. BUT: with this setup the grounding tab does not connect to anything!

If I were to get another cord I would get the round connector so that the engine / heater is properly grounded.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

While working on coolant leak, I noticed block heater cord still dangling there. I must take it out. It is the round type and won't fit the present block heater. Should go buy the other type. But with good engine, car garaged and magnetic heater for super cold days, I don't really need the block heater.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5