Why are diesel engines so hard to start in the winter? Does the cold prevent the glow plugs from heating up? Also, what can I do if my diesel truck doesn’t start on a cold winter morning? Put the plugs under my armit? 
When the motor is cold, the fuel that is injected condenses on the cylinder walls making it difficult to ignite. Most diesels are equipped with a block heater in the guise of a electical plug. If you have one, just run an extension cord to the nearest recepticle. Not only will your diesel start quickly, but you’ll get blissful heat nearly instantly.
They draw about the same wattage as a lighbulb.
If your motor is not equipped with a block heater get one. Not only will you have easier starts, it’ll let your motor get oil more quickly and prevent dilution of the motor oil with diesel.
Another possibility is that your diesel is gelling in the cold temperatures, but the oil companies typically mix diesel for colder climes to avoid such problems. If you are gelling, a small amount of kerosene in the tank will solve that problem, but I bet the problem is the cold block.
But you could try the armpit idea and let us know how it turns out.
I don’t know much about diesel trucks, but I have experienced this with tractors, diesel mowers, etc. They usually have a switch on them that you press and hold to heat up the glow plugs, after about 5 secs. (or more/less depending on temp.) they fire up. If there isn’t that type of switch on your truck, I don’t know what to tell you. I suppose you could let it run all night, but fuel/neighbor problems may arise, it’s a diesel though so running it all night wouldn’t be harmful on the engine (I know, that suggestion isn’t feasible). Hmm…let me know how the armpit thing works!
Seriously though, I don’t see why they wouldn’t have some kind of button/switch like tractors have, unless it’s done electronically, then that’s a whole other problem.
>> Why are diesel engines so hard to start in the winter?
Because they’re cold. The mixture has to auto-ignite by compression and it is easier to reach the necessary temperature if you start out hot. The glow plugs just heat the air. Diesel motors are also harder to start because they have more compression and are harder to crank. I have a diesel on my boat with no glow plugs. Lovely
Here are some things I have done and do:
1- Use the decompressor if you have that. If you decompress, the motor will turn with no effort and when it has gathered momentum you compress and it will start pretty easily.
2- Use starting fluid. You spary a bit in the intake and it works like a charm. Do NOT use starting fluid AND glow plugs as the fluid is extremely flammable.
3- Heat the admission collector with a blowtorch. This does the same as the glow plugs except much quicker and better.
4- Direct the hot air from a hair dryer to the air intake.
A combination of the above will guarantee a quick start on any diesel.
If you live in very cold weather and starting is a problem very often, you can get an electric heater you can plug in the mains and will heat the block. That will also make a huge difference in that the motor starts out much wormer which is better for it. Buses and large trucks have a separate heater which burns fuel and heats the cooling fluid so the engine will be warm when it is first started.
Diesel fuel comes in different grades and some may start better than others. I know some people who have boats which do not start up well will mix a small percentage of gasoline into thier diesel fuel and this makes it easier to start. You have to be careful though because diesel lubricates the injectors and gasoline does not so you cannot mix too much. Just enough.
So I guess it isn’t as simple as my JD tractor, ok then, was just trying to help (told you I knew nothing about diesel trucks). But, seriously, why don’t they have a switch to heat up the plugs? Or do they? Anyhow, I did learn something about diesels, in case I ever get one, for what reason I have no idea…
cw, most trucks do have glow plugs but having glow plugs is not a guarantee that the motor will start. First, the glow plugs drain the battery when you most need it. Also, they can fail. And, in extremely old weather it may be difficult to start even with glowplugs.
Thanks for all your replies. My truck doesn’t have a block heater so I will have to try and find one. I’ve never seen one here in Korea but they must be for sale somewhere. It gets really cold here up north. The truck has spark plugs and you warm them up by turning the key to the ‘on’ position. After about 5 seconds the little indicator light goes out and the engine is theoretically ready to start. It’s only failed to start once when the temperature dropped to -20 Celcius. I’ll have to see my local mechanic about getting a block heater and see what he thinks about other methods. No, not my local mechanic – he causes more trouble than he cures. I’ll go to the offical Kia service station and ask them.
By the way, is a block heater expensive? How does it work? I mean, I know it keeps the engine warm but what part of the engine?
Thanks for all your help.
>> The truck has spark plugs
They are glow plugs. Different animal.
>> is a block heater expensive? How does it work?
It should not be expensive if your engine is designed to take one. It just goes in the block, in the cooling fluid, and just warms up the entire block so the cylinders are warm. As you can see, you just want to heat the air and/or engine and there are many ways to do it. Glow plugs are just the most convenient but possibly the least effective. You could even drain the coolant, heat it over the stove and then pour it in the engine again.
Right, ‘glow plugs’. Sorry. Writing ‘spark plugs’ is force of habit since I’m not used to having a diesel vehicle.
I don’t think your problem has anything to do with the temperature of the engine at all. It is your fuel. An ingredient in diesel fuel is parafin wax. When the temperature gets too cold, the parafin will start to coagulate. When this happens, the fuel won’t flow. You can buy anticoagulant additives for diesel, it keeps the fuel liquid but will result in some black smoke at the tail pipe. Learned all this last week from watching Two Guys Garage. And they have some nice pictures here that show what I am talking about.
Hmm, the Two Guys site does not allow deeplinking. To find the example of frozen diesel from the links in my previous post, click previous shows, High pressure diesel, then fuel woes.
What?
As I said, diesel fuel characteristics can be improved in extremely cold weather to make it more fluid and more flammable, which will make for better starting. You can add expensive additives or mix in some gasoline. But To say the only cause of poor starting is the fuel is just silly. Everything counts. Besides, Fuiel injectors work at tremendous pressures and the fuel being a bit less fluid is not going to make much difference. Note also thatthe fuel return to the tank carries warm fuel and so, as the motor is running, the fuel in the tank is getting a bit warmer.
A co-worker had terrible problems with his diesel car in very cold weather. The fuel would jell in the cold. He tried all the aforementioned methods, with poor results. Then he talked to a guy who drove big trucks for a living. The driver told him how to mix alcohol in the fuel and how much to add. Tom bought the stuff at a truck stop, and he never again had starting troubles in the cold. I don’t know the ratio, but a truck driver can tell you.
Mixing alcohol in diesel fuel is a terribly bad idea for several reasons and it will not help starting half as much as gasoline or specific additives. I don’t reccomend it.