Block Heater: How Long To Leave It Plugged In?
 

Hey everyone,

I tried searching to find the specific answer to my question before posting, but I didn't seem to find it...

I'm in Nashville, TN and our temps are getting down to between 6F-12F overnight this week. I couldn't get her to start this morning, and she had been sitting cold for two days and it's stayed in the 20s during the day lately. How long should I keep her plugged in for? Is it something I just need to do an hour or so before I leave in the mornings, or should she stay plugged up overnight? Thanks!

RF

If you leave it plugged in overnight, in the morning it will start like it's 75F outside.

'87 300SDL 275,000
'94 SL 500 50,000

I'm a little surprised the car didn't start, so let me ask this:

1. Did you consider running the glow cycle twice?
2. Have the valves been adjusted within the past year?
3. Is the battery well charged?
4. Do you use synthetic oil? Also significant.

Valve adjustment seems absolutely essential for good starting in cold weather. All my past problems have dealt with that.

I have a functioning block heater and use it only when the temp gets close to 0 degrees. I let it run for about two hours before starting and the car starts well, without needing to use the idle increase. I do crank it up a little after it starts, to warm it faster so the car is toasty warm when I get in, to drive. Plus the trans will also be warmed up.

Hope this helps. My car is not garaged over night so being out in the cold

Four hours seems to be a good number (use a timer set for four hours before you want to start the car). Overnight is good too, costs a couple of pennies extra for the electricity (about 400 Watts for a factory block heater, about 600 for the lower radiator hose aftermarket heater).

I drive an aging 1986 Golf diesel to work, have it set on a timer to come on at 4am so it should be nice and warm at 6:15 when I start the car. The timer was set to kick on around 4:45am but with our current weather situation of below zero I pushed it back to four.

Having said that I have been known to leave a vehicle plugged in for the better part of a day on the weekend just in case I needed it to go somewhere, and that goes for the W140, which has 15w40 oil in it.

I think two to four hours is sufficient depending on outside temperature, any more than that might be waste but when it's this cold out I would prefer to err on the too long side.

my .02

steve a

Thanks for the tips guys....

I think I do need to have the valves adjusted... The PO said it had not been long since it had been done, but I'm not totally sure about that. I did let it run through a few full glow plug cycles, and the plugs are all working.

So other than it costing a few more bucks on your power bill, there's not anything BAD for the car to leave it plugged in overnight is there? That was my main concern..... It being bad for the car...

Won't hurt the engine or the block heater to leave it plugged in all the time so long as you remember to unplug before driving.

Cold weather
 

MBinNashville- I feel your pain. I'm in Smyrna and just check the weather on the internet and with the wind chill we're at 4 degrees. I had to go into work this morning- went to start my 300D up and no luck. Let the GP's cycle through one more time and it started up. Funny thing is, when I left work (in Brentwood) I had to cycle them four or five times until it started. Didn't even turn over. I was thinking the battery was dead but I've put two batteries in this car over the past two years or so. I know I've got some electrical gremlins but can they be causing the battery to die this quickly. It's an MB battery.

My brother has a 300CD and had trouble starting his this morning too. He just had a local guy do a valve adjustment on his a couple months ago and was running fine since. All our cars are FL cars so they're not used to this type of weather- also, being FL cars they don't have block heaters. It doesn't help either we live in an apartment complex so our cars are parked outside too. We're going to give our cars a little run tonight before going to bed so they warm up a little.

Good luck!

-DieselClan

I have an 87 300 sdl. Does this car have an idle increase on it and if so where is it.

Mike

I heard on the weather channel that wind chill only effects human skin. If its 20 degrees outside with a wind chill of say 5 degrees our cars feel the 20 number. Anone confirm if this is true? Mike

yes, It is true. Wind chill only applies to naked humans.

Mbnashville, Two hours plugged in is all I have ever needed in Monteagle.

I have the timer set to turn on at 4:30 for a 7 to 8 am start. The timer are set to shut off at 10 if we don't leave early.
It is worth the peace of mind to ease the cold start strain too.

Wind chill would only apply if the object or person is warmer than the air blowing over it. Convection is a very efficient means of heat transfer but there needs to be a diffference in temperature between the air moving over the object and the object being cooled. In the case of a cold engine, it should be the same temperature as the ambient air and therefore the air cannot make it colder.

Originally I started on Citroens and truck diesels, so my thinking is a bit different. One observation: Mercedes cars, especially diesels, depend a lot more than some cars on good electrical grounds, and being that the cars here are usually older, I am not surprised that some grounds have weakened or gone bad. Once I adjusted the valves and replaced and repositioned my ground cable, I have never had a problem with starting.

Shorts and electrical "gremlins" are a big problem on older Citroens, which are 6v. Usually these cars are 40-65 years old, so the best thing to do is replace all wiring, bit by bit, after checking the function of the various motors such as WSW or starter.

I was amazed at how much better the MB diesels I've had will start after redoing the grounds.

Wires can fool you. I bought a Citroen from a museum and couldn't get it to run to save my life. I went through wire by wire and found the wire ebtween the coil and the distributor had corroded through after 20 years, but the outside wire had been waxed and polished for display purposes and you never would have known.

50 cents worth of wire later, the car was running.

Moral: Check your grounds and all contact points in the GP system for maximum delivery to the cylinders, and maximum starter speed to get the vehicle rolling once the cylinders have been warmed.

One hour should get you started. Two hours would allow for a easier start. A lot deppends on the condittion of your engine and whether you are just using it as a starting aid or trying to get the whole block to operating temps:P