Hi When starting a 7.3 in cold weather without waiting for glow plugs the motor turns over regular then sounds like it spins Different and won't start. Is this normal? If I wait for plugs I have no problem. Thanks

 

You understand the whole theory of how diesels work, Right? You don't work the glow plugs, You get no Fire.... No Bueno.

 

Well, that does depend on the weather where a person lives, too.

Here where I live it's rarely cold enough for me to have to wait before I start my engine.

Stewart

 

Yeah about 90% of the time I forget to wait... New to the diesel thing and I just forget to wait. It never hesitates to start right up? Anyone know about at what temp. It starts becoming an issue?

 

Totally dependent on a bunch of different factors.

Diesel engines are "compression ignition." The piston compresses the air in the cylinder to a very very small percentage of the full volume of the stroke. When air is compressed, it heats up. Then, at the top of the compression stroke, fuel is injected in to the cylinder, and, if all is working as designed, the compressed air is hot enough that the fuel ignites, resulting in the power stroke of the piston.

If the engine can't compress the air enough to reach the requisite temperature, then the air/fuel mixture won't ignite. Glow plugs are intended to help heat up the air in the cylinder to aid in firing.

Battery and starter strength, compression, air temperature and the temperature of the block and other metal components all come in to play. A weak engine will have trouble starting even in above freezing temperatures, while a healthy one will start without issue in sub-freezing temperatures even if all the glow plugs aren't working.

 

Battery and starter strength, compression, air temperature and the temperature of the block and other metal components all come in to play. A weak engine will have trouble starting even in above freezing temperatures, while a healthy one will start without issue in sub-freezing temperatures even if all the glow plugs aren't working

A weak engine as in, a low compression engine, or weak engine as in, a weak component that you mentioned, resulting in a non fire situation

 

I've forgotten a few times and it cranks up just like normal. But I don't live where we get sub-freezing temps. I've wondered if it's bad for the engine at all but it doesn't seem like it would be.

 

Either one.

Worn rings will prevent the engine from building adequate compression, as will a worn starter or weak batteries.

 

Thanks for the detailed replies. Explaining what is going on internally helps me realize that the glow plugs are just a starting aid and not a requirement. Thanks again for the clarification. Another reason to love this site.

 

I put a LED light that is hooked up to my glow plug relay. When power is going to my glow plugs this light is on. IMO, it is always better to let the engine do what it was designed to do.

Warm cylinders should cause your engine to start sooner and should require less fuel to start. Your starter may also last longer by not having to crank so long.

This little red light may stay on for a minute or longer, depending on how cold it is..



BBD

 

Glow plugs allowed to warm or not, starting a cold engine for me doesn't take any longer, nor is it shorter when I let the plugs warm, so that's not an issue either.

Stewart

 

I have one of these:


Pretty easy to tell when the plugs are on with this.

 

The warm climate guys likely don't need to let the glow plugs cycle.

I had 6 / 8 glow plugs fail, truck would hardly start around freezing point....

 

I watch my voltage too. I have an led that lets me know, but the voltage drop is a dead give away. Jumps from 11 to 14v.

 

I rarely give my glow plugs time to cycle.