Diesel engines behave very differently than gas engines during the winter, especially starting and right after start up. This month’s tech article will explain what you need to know for operating your Power Stroke during the winter. First we’ll talk about how all of the cold weather systems on the engine work, and what you should expect from your truck during cold weather. After that, we’ll explain what you can do to keep your Power Stroke running in top condition as the winter moves in.
Starting Your Truck
Diesel engines work on the concept of compression ignition; as the air in the cylinder is compressed, it is heated to the ignition point of the fuel. If the air being brought into the engine is too cold, it may not get heated enough to ignite the fuel, or to fully burn it. This is why diesels are traditionally difficult to start in the winter time.
The glow plug system is the primary way of assisting the engine startup. When the engine oil is less than 131° F, the powertrain control module (PCM) will energize the glow plug relay, causing the glow plugs to turn on and heat the air inside the combustion chamber. The PCM will keep the glow plug relay energized for up to 2 minutes, depending on the engine oil temperature, the barometric pressure, and the battery voltage. The colder the oil temperature, the longer the glow plug relay will be energized.
This allows the engine to start even when the outside air temperature is very low. If the PCM detects that the altitude is 7000 feet or greater, based on the reading of the barometric pressure sensor, then it will add an additional 5 seconds to the glow plug on time. I have personally started my truck at -18° F without using the block heater; however, this requires strong batteries and a good working glow plug system. For more information about the glow plug on time, see the glow plug on time spreadsheet under More Resources.
The PCM also controls the wait to start light in the instrument cluster, which Ford refers to as the glow plug indicator. This is really a horrible name for it, because in reality it has very little to do with the glow plug system. It is controlled independently of the glow plug relay.
The glow plug indicator is supposed to tell you, the driver, when the engine is ready to be started. However, the PCM turns the light on every time the ignition key is cycled, in order to test the bulb, even if the glow plugs are not turned on. Also, the glow plugs often continue to run after the indicator has shut off. The normal on time for the glow plug indicator is one to ten seconds. On very cold mornings