Project Box Hauler: Glow Plugs

July 19th, 2010

By: Kevin Wilson

Photos: Kevin Wilson

Here’s the complete set of Diesel Rx 7.3L Power Stroke glow plugs. Note the tips are slightly discolored from testing.

Glow & Go
Installing New Glow Plugs Will Fix Cold Start Woes

Since diesels are compression-ignition engines, meaning there are no spark plugs to start the combustion process, nearly every diesel is equipped with some sort of glow plug system to get the fire started in cold weather. The little “Wait to Start” light that comes on usually indicates that the factory glow plug system is activated as part of the cold start circuit. Today’s computer-controlled engines have taken the glow plug system engagement to an all-new level, taking into account the various engine parameters as to when the glow plugs will be activated or not.

Like any other mechanical part, glow plugs get tired over time and eventually need to be replaced. Since we were pulling the valve covers off the Project Box Hauler to do a compression test on our 200,000-mile project Super Duty, we figured it was tim e to toss a new set of glow plugs in the old 7.3L Power Stroke. The typical indication of a possible glow plug problem is poor cold starts, or the fact the truck won’t start at all in cold weather without being pre-warmed with a block heater. A solenoid-type controller activates the 7.3L glow plugs and that too can be a source of trouble, especially if it has bad connections or was replaced with a cheapie parts store solenoid, according to Nate Brekken of Strictly Diesel in Scottsdale, Ariz.

There are several different types of glow plugs, and this illustration from Diesel Rx shows the internal components of a typical glow plug.

Diesel Rx, the consumer division of WAP, Inc., (formerly Wellman Automotive Products), is the single largest domestic manufacturer of glow plugs left in America. WAP supplies glow plugs for a variety of diesel manufacturers including GM, Ford, Mercedes to name a few, along with units for the military HUMVEE and the big diesel folks such as International Harvester, Case, John Deere and Caterpillar. Diesel Rx also handles OEM replacement fuel injectors, glow plug controllers, fuel pumps and feed pumps from its Shelbyville, Ind., facility.

Diesel glow plugs are an integral part of the cold start process.

So it was a no-brainer to have Diesel Rx send us a new set of glow plugs for Project Box Hauler, along with a new glow plug controller solenoid. Installation is relatively easy, once you get the valve covers off the Power Stroke, which is the hard part of the job. While you’re in there, it might also be a good time to inspect, test and replace any bad fuel injectors. The Ford experts at Strictly Diesel made the glow plug swap look easy, and the process is outlined in the following photos.

If your diesel is having trouble starting, especially when cold, it might be time for new glow plugs, especially if the odometer has a lot of miles on it. Replacements are relatively inexpensive, and will buy you some peace of mind and easy starts on those cold winter mornings. While you’re at it, it’s good insurance to replace the control unit, as well.

Diesel Rx
(877) 421-3187

Strictly Diesel
(480) 922-8768

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