How long can I leave the block heater plugged in? It was around 20 deg. F this morning and I'm afraid of beating up the starter with the kind of start she had today. Do I plug it up for a few minutes or leave it plugged in overnite?

Block heater is an electric resistance heater and will take several hours to soak the block. I think they are designed to work overnight. I have no experience only general knowledge of what I have read - Alabama winters are pretty mild and I keep my 240D in the garage (have not used the heater).

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

If you plug it in for only 3 minutes, you might as well plug it in your ear. It takes hours to warm the engine with the electrical block heater. However, since the engine will usually start OK at 30F, an hour should be sufficient. It it was below 0F, you should leave it on overnight. It won't overheat.

P E H

A lot of people have told me to plug it in for an hour and a half or two hours before use.

Alex

I'll put it on a timer to come on at 3:00 a.m. Thanks.

Greetings All,

After reading all the posts on this topic I'd say that two hours should be enough to get the engine coolant temp where starting is quite a bit easier than at ambient temps of zero or above. Of course if your temps stay around minus zero temps, I'd add another hour to insure an easy start. So far down to 10 degrees F I've had no problems with a no plug in situation, but I'm sure an hour of heating would bring engine temps to normal at starting. If you choose to use a timer to do your dirty work, please insure you buy the upgraded timer that actually is rated at 20 amps to insure the thing works on a better level. Seems like the cheap ones end up stopping after only a week or so. There's a $4.00 difference between the grades, but it's worth it.


Charles

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'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Current draw of the block heater isn't near 20 amps. I would guess it is about 500W which is about 4 amperes. I'm saying that because I had a 1200W tank type heater on another MB and in an hour it had the entire engine so that it felt warm to the touch, almost as if it had been shut off a short time ago. The original block heater isn't any where near that capacity.

P E H

I just installed a block heater in my 300D and it is rated at 400 watts (the car has to live outside of the garage this winter). The heater is made by Zerostat/Temro in Canada for M-B (220D, 230, 240D, 300D, 450SL/SEL). Believe it or not, the instructions do not say anything about how long it needs to be on to warm the coolant enough to ease starting! I researched other posts on this site and the consensus was 2-3 hours, with 3 hours needed when it is colder (10-20 degrees F. and colder). However, no one mentioned the wattage of the block heater which has a large impact on how long it needs to be on.

As I recall, an extension cord with 16 gauge wire should work fine (up to 100'). 400 watts divided by 110 volts = 3.636363 amps.

Good luck!
Tom

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1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
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Which ever diesel I plan on using the next day, I plug that one in the night before. If I need the car for 7 am, I am not going to get up at 4 am to plug it in. Here in NJ it has been getting down to the low 20's at night, so I have been plugging the cars in. Anything to make the battery/starter work less, the better.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
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As a tangent to this discussion;
Is there any problem plugging in the block heater for the night when I return home from work and the car is already warm?

Currently I have a timer that turns on three hours before I leave. I have a garage in an apartment complex and don't pay (directly) for the electricity in the garage.

I solved this problem a different way. I moved to Texas.

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Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

No electricity?

No Brass Monkeys !!

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

Touche.

I wouldn't plug in the block heater when the engine is hot from running. It may cause cavitation and corrode the heating element. Also the extra "on time" may shorten its life.
P E H