Sorry for this newbie-type question. I have a 1985 300TD turbo wagon but Euro grey market version. It came with no engine black heater, or for that matter, no frills. Its manual everything (vs. power windows for US version).

Anyway, I've owned this wagon for a good 4 years now, pretty much living with no engine block heater while living in New England. The car of course won't start up when the temperature dips below 25 degrees F, even with brand new glow plugs and proper diesel, the car just refuses to start.

By contrast, I also own a 1983 300SD. In the middle of last winter, when it was below 10 degrees outside, because of the block heater, the car started at first crank even when the glow plug fuse went, and one of the plugs was bad as well.

I see that block heaters can be bought really cheap, and that they are supposed to replace the radiator plug. Am I right? Do I need to drain all the radiator coolant first? Are there any installation instructions/tips/tricks I can follow?