Why are there no glow plugs?

[Diesel Dan]

This morning I started the bus in 35 degree weather just to see how it would do without plugging in the block heater. The cranking was very sluggish, but it started on the second try. I still don't understand why it is that my bus has no glow plugs (DT466). Both my Ford F250 (7.3 liter IDI) and my Mercedes 300D (3 liter IDI) have glow plugs, so that is what I'm accustomed to. Neither of those vehicles would start on a 35 degree day without glowing the plugs. Does anyone know how it is that bus engines are able to pull this off? I know the DT466 is direct injection, as opposed to my other vehicles, but I think the newer F250's are also DI and they have glow plugs. So what's the deal with this?

[Jarlaxle]

The DT466 doesn't need them. Most larger diesels have no glow plugs...even the 5.9 Cummins doesn't use them. Until recently, many had no starting aids at all.

[Diesel Dan]

Well, yeah I understand how diesel engines work, with the higher compression igniting the fuel without spark; but if the 7.3 liter international engine in my F250 has glow plugs, and really will not start well without them, then how is it that a DT360 (5.9 liters) international (and the 5.9 cummins) doesn't need them? Heck, even my DT466 (7.6 liters) is only slightly larger than my F250's 7.3 engine. And again, I will reitterate that the Ford Powerstroke diesels (6.9 and 7.3 liters) use glowplugs, and have direct injection and these engines are used in Ford pickup trucks and in International school buses. Same goes for the older 7.3 IDI engines. I just don't get it...

Ah well, it doesn't really matter. Just an academic question really. But inquiring minds want to know!

[Jarlaxle]

The DT360/408/466/530/570 is a superior design compared to the 7.3 PSD/T444E, not needing the crutch of glow plugs to start when cold. Most large diesels do not have them...many now have intake heat grids, but that is more for cold-start emissions than anything else.

[Diesel Dan]

Originally Posted by Jarlaxle

...many now have intake heat grids, but that is more for cold-start emissions than anything else.

Cold start emissions... heh... We recently had some 20F weather here in Austin, and I couldn't plug in my block heater on my Ford F250 with the 7.3 IDI during the day since I was parked at the office where I work. It wasn't too happy about starting even with a long glow plug cycle, and when it fired up it ran rough at first. Man, you shoulda seen the cloud of smoke that drifted across the parking lot of my office building!