People who drive gas powered cars made in the last 20 years generally don't pay any attention to temperature. Those of us with older diesels (23 and 25!) do, at ~10F my 240D will get a little ornery at -10F it'd be difficult and at -20F it won't start without help. With the magic of the block heater it'll start no problem at all temps.
Anyway if you take a look at Youtube there are tons of coldstart videos. The interesting thing I find in those is that they're mostly from metric countries (not the US basically) so you get "Coldstart, 10C" or "Coldstart -10C".
This winter will be the 6th in which I've driven a diesel car, so 3 winters each the 240D and the 190D plus one winter screwing around with my 300TD. The 190D has a more modern engine and starts WAY easier than the 240D but either way I figure I've got a masters degree in diesel engine cold starts. Let me start by saying -10C isn't cold... Thats 14F which isn't even the beginning of cold. Cold starts at -10F, real cold starts at 0F and bitterly cold starts at -10F. Here in central MA we can expect one or two mornings a winter at -20F which is the start of take your breath away cold. The guys in the extreme north scoff at all this of course.
Anyway what follows here is what you need to know to start your old diesel Mercedes in the cold. This should basically apply to other makes too but I dunno...
#1. Throw that starting fluid away and smack yourself for even suggesting it. The MB is an indirect injection diesel with glowplugs, you use that crap you'll crack a prechamber and the engine is toast.
#2. If your battery is older than 3 years its automatically suspect, if its older than 5 you need to replace it. Don't kid yourself into thinking you can get "just one more year" out of it, you can't. I spent one miserable winter where the 240D wouldn't start even at 15F because the battery was bad. It finally failed completely and I was amazed when a new battery fixed a host of issues. If the battery is older than the toddler next door it needs replacing.
#3. Synthetic oil is your friend, Mobil 1 5w40 is best followed by 0w40. I'm not a huge fan of the 0w40 as my cars both clattered a bit more with it, I don't think it hurt anything but still... 15w50 will do in a pinch if its all you can get. 15w50 will still flow better than conventional 15w40 at cold temps but the other two choices will flow better still. Put a bottle of conventional 15w40 oil in the freezer and you'll see it turns into honey. How well is that honey lubricating your engine when its cold out? If you've got a block heater you can get away with conventional oil but remember you might want to travel somewhere that plugging in isn't an option...
#4. Glow plugs. Marshall used to chide me for my suggesting to change the glowplugs before they failed. He said that glowplugs would go 100,000 miles without being changed. I contend that when glowplugs fail its always at the least opportune time. If you've ever change glowplugs outside at -10F (I have!) you know what I mean.
#5. Water is the enemy. It'll condense into your fuel tank then freeze and you're in trouble. It'll also give a place for algae to live. Treat your fuel tank with a water remover at least once in the fall. I use isopropyl alcohol at 2x the recommended strength once in October sometime. Then I run a bottle of Diesel Kleen (from PowerService) in Novemeber sometime. I use a whole bottle of Diesel Kleen in about 1/4 tank of fuel which is probably 10x the recommended concentration but I never have water or gelling issues.
#6. Make sure you've got winter fuel. When I first got my 190D it had been sitting for months and had summer fuel in it. It would start but wouldn't go in any gear but first. I put a full bottle of Diesel Kleen in and ran it. That car has a fuel thermostat that heats the fuel so after 20 minutes or so I could drive fine. I drove until the tank was mostly empty and refilled.
-The actual cold start -
So its -10F out and you need to start your car. Lets say you don't have anywhere to plug it in either. When I was driving the 240D that was how things went most of the time for me as we lived in an apartment...
Okay get in the car, turn off all electrical loads. You made sure to turn off the wipers last night right? Make sure the heater fan is off too. We're going to need every amp available. Key on, the glowplug light should come on. Wait the 20 seconds or so until the light goes out and then wait 10 seconds more. Cycle the key back to off and then on, wait the 20 seconds again and then again 10 seconds more.
You're only going to get one shot at this, if the car doesn't start you're in the hurt...
Pump the throttle (gas pedal) to the floor 3 times, then hold it all the way down, FULL THROTTLE!
Okay key to start, the engine cranks, HOLD THE KEY ON START. Yeah I know, your dad told you to only crank for a couple seconds, he told you you'd ruin the starter otherwise because it'd overheat. Hey, its -10F, its not going to overheat. If you stop cranking now the car will be harder to start than if you don't and it will thus put more wear on the starter, crank until it starts. This is what momma benz says to do and thus the best thing for your car... Except maybe for my alternate start method, more on that later.
Within 20 seconds you should start to hear encouraging noises. If your battery starts to die at this point it needs replacing, even if the car does start. The battery should be able to crank for a good minute at this temp without dying. The encouraging noises should get more and more consistant (pop.....pop, pop......pop, pop,pop.....pop,pop,pop,pop...etc) don't give up yet keep at it until the car is actually running. Once the encouraging noises are mostly constant release the key and ease back on the throttle. On these older cars when its real cold out if you come off throttle too fast at this point lots of times they'll die, so ease back on the throttle, keep it at high idle for maybe a minute. You've used up a lot of what your battery had to offer, if the car dies now you might have a hard time restarting. My 240D has a high idle knob for situations like this, it'll keep the idle above what it normally would be. I've never had it working enough to try it. I've bought all the parts so I hope to try it out this winter.
So your car is running, take off eh? DON'T hang around waiting for it to warm up. All cars warm up best (most quickly, most evenly) by driving around. That isn't to say romp on it and merge with freeway traffic right away, drive easy for a mile or two and you'll be all set.
-Curt's alternate diesel Mercedes starting proceedure-
So the above didn't work, or you've got bad glow plugs or a bad battery or heavy oil or your block heater croaked or its -20F and your 240D won't start no matter what, what now? I had this a lot that year the battery in my 240D wasn't any good.
Start your pickup truck, its a gasser right? It always starts, no worries. Why do you drive a diesel then? Well economy of course.
Go wake up your wife, you'll need help for this. Get out the strap and connect the pickup to the car.
Let your wife drive the pickup, give her CLEAR instructions on where to go and how fast to drive. Don't make her guess about anything and remember not to yell at her.
Your car is manual trans right? So she doesn't have to pull you very fast so lets say 25mph. A fullsize pickup is better at this but any truck (or car) will do a smaller vehicle may have traction problems so your tower may have to go faster, you'll need to experiment.
So at 25mph you put the car in 2nd gear (maybe 3rd, experiment) and ease out the clutch. Don't just dump the clutch or the tow vehicle may lose traction... Ease out the clutch and you should hear the engine cranking over. You may need to let it crank over for awhile (especially at -20F) before it'll fire. Careful with the throttle here, you don't want to smack into your tow vehicle! Once the car is running and everybody's stopped get out and take the strap off. Put the strap in your car with you, you might need it later...
Thank your wife, appologize for yelling at her, bring her something nice that evening.