My car came with a big 110v AC plug behind the grill and today I figured I'd plug it in. I had always thought that block heaters were just electric blanket deals so I was surprised that mine made noise. It sounded like an electric motor running. The wire just goes into a big plug screwed into the block behind/under the turbo. It was puling some current because the cord was warm after a few minutes.

So how do these things work?

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My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

Normally just a heating element similar to what you would find in an electric kettel. Plug it in and it gets hot. After 30+ years it may have corroded (most are copper) or have large deposits on it causing the noise and excessive current draw.

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1982 300sd, new project car to restore

It doesn't matter if you know what you're doing, as long as you look like you know what you're doing.

Or it could be operating normally. I've had ones I could hear and the cord does get warm since it's drawing current through it.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

yours could be an aftermarket one. some are in the heater hoses, with pumps to circulate the coolant.
but like mentioned, you are likely just hearing the water boiling off the elements.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
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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!

The standard MB Block heatyer is just a little heating element that heats the coolant in the water jacket. fits into the side of the engine on the right side in front of the starter.


this is one shown in Fast Lane.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I just had an OEM block heater installed and it works great! Little expensive, but definitely worth it in a cold climate like mine.

As the others have said, check for corrosion since all the fittings are at least a quarter of a century old. A bunch of parts on mine were corroded so I had everything replaced.

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Never be ashamed to ask for help.

1985 300D
1987 300SDL
1970 Jaguar E-Type OTS
2002 Dodge Intrepid (Traded In)
2011 Ford Crown Victoria

My blockheaters have always made a little sizzling noise from the coolant being in contact with the heater element.

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The noise is analogous to a kettle "singing" when it's on the stove. Has to do with tiny water bubbles forming and breaking, I think. Click and Clack would know.

The block heater should take about 4 hours from stone cold to easy-start warm. You'll also have heat in the cabin almost immediately. If you don't want to leave the block heater on all night (it draws a good 400 Watts and the aftermarket ones even more) you can set up a timer to turn on the block heater 4 hours before you need the car to start.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Be sure that your extension cord is an appropriate gauge for a block heater. They do draw a lot of current and the longer the run of cord the bigger gauge wire it should be. If the gauge is too small it could be the reason the cord is getting hot.

Thanks for the pic Charlie!! I'm thinking about adding one to my 240d.

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2006 Jetta TDI DSG 320k miles
1997 Ford F150 325k miles 4.2L V6 "Work Truck"
2008 Tundra 225k miles 5.7L
1982 240D.....sold
1984 300D...Totaled OUCH!
1985 300D Turbo 222k miles "Dos" sold to 79Mercy
1986 300SDL 98K miles "The Beater"....sold
1987 190E 2.3 16v Euro spec 115K miles....sold

They are nice to have on those cold mornings. I have a lower radiator hose heater in my 240, it was free and convenient. It helps but it's not as good as a real block heater. Also getting the freeze plugs out of the block and be REALLY hard, so a lower radiator hose heater is easier to install.

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The PO of my car installed a small battery trickle charger and wired it to the same cord as the block heater, so plugging the car in both preheats the engine and tops off the battery. I thought that was pretty clever.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

That's a pretty damned good idea actually.

Quite clever.
Is there any downside to trickle charging a battery constantly?

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I think it would depend on the rate of charge. I mean people put battery tenders on their motorcycles all winter to save the battery's so it cant be bad for them.