JoeAugust,

One thing it isn't is glow plugs. They only aid starting and once the engine is started, the GP are turned off and have no effect on the runing of the engine. It isn't bad fuel either. I you got dirty fuel, the engine would just have reduced power from a plugged filter but wouldn't misfire or smoke grey.

Don't let anyone tell you the GP should be replaced.

Greyish smoke usually means unburned fuel. It seems like something has happened to one or more of your cylinders to cause a compression loss and the cylinders are not firing. Could be a head gasket leaking between 2 cylinders without much leakage into the cooling system.

A compression test would be in order.

P E H