1985 M Benz 300 Turbodiesel

How do I install a block heater on my '85 M Benz 300 turbodiesel?

First, make sure there’s not already one installed. Most 300D’s imported to North America came with a factory installed block heater. Some, if they went to warm weather states, never had them hooked up. There is a detachable cord that plugs into the heater and is then routed forward through the grill. If the cord is missing it can be purchased for about $15 at the dealer or aftermarket.

To see if your 300D has the block heater, look on the right (passenger) side of the engine block from underneath, and it’ll be about halfway up. It will be round and about 1 1/2" across, threaded into the block. It’ll have a three prong electrical connection showing. The cord simply plugs into the connection.

If your 300D didn’t come with the factory heater you’ll just see a metal threaded plug in the opening. You’ll see a way to attach a socket to the plug to remove it which allows the factory heater to screw in. This is in theory only though, because removing the plug out of the block after 25 years will be near impossible! I have had the cars up on a hoist, using a 3/4" drive breaker bar and a 4’ cheater handle and was still unable to break the plug loose. There is a real danger of breaking a chunk out of the block itself trying to get the plug out, which would result in a new block.

My advise is, if there’s not already a factory installed heater that just needs the cord then don’t try to remove the plug to install one. An inline heater in the lower radiator hose would be the next best option.

I used an inexpensive dip-stick heater in mine and it worked pretty good…Whatever type you use, you need at least 100 watts to get the job done. Some block heaters are 500 watts!

benzman is correct. I owned to 1985 300-DT’s and they both had block heaters in them. I think that the electrical cord had to be soldered on though and not simply plugged into the heater. I’m not certain of that though.