Diesel Engine Glow Plugs Vs Intake Heaters: What's The Difference?

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Over the last century or so, the auto industry has changed in a myriad of incredible ways. It's mind-boggling to think of just how far we've come. What would the drivers of 1925 have thought if they'd seen the audacious and polarizing Tesla Cybertruck, for instance, or any one of Volkswagen's formidable diesel engines? Despite the incredible technical advancements we've seen, there are some problems that the industry has been grappling with for decades. One is that our vehicles just don't like getting started on cold days — no more than the frustrated drivers behind their wheels.

That tired sputter on a chilly winter morning has exasperated almost every driver at one point or another; it's a bit of a rite of passage. It's such a common problem that auto manufacturers have developed mechanisms that attempt to eliminate the issue, or at least help mitigate it as much as possible. Two such features are a diesel engine's glow plugs and intake heaters. Both were designed to help diesel fuel combustion, particularly when the engine or ambient air are cold. An intake heater warms all of the air going into the engine's cylinders, while glow plugs in each combustion chamber provide a little extra heat before ignition. While these two components both use electricity to heat air to help the fuel burn better, their mechanisms and designs are quite different.

Diesel engines use glow plugs instead of spark plugs. The two components are similar but work in very different ways. Diesel engines use compression ignition, where the piston compresses the air, heating it enough to combust the fuel. Gasoline engines use spark ignition, where an electrical spark at the tip of each plug ignites the fuel-air mist. Glow plugs are mounted in the combustion chambers and are activated when the vehicle is powered on. Their heated tips help raise the temperature in the chambers to a point where the fuel will combust properly, and they are especially helpful when the outside temperature is low. Glow plugs have a post-ignition role too, and will often stay heated for a short time after the engine starts to help maintain performance.

First used by Bosch in 1922, glow plugs are now either ceramic or made of highly conductive metals like platinum or nickel-chromium alloys. Ceramic glow plugs work a little more efficiently and quickly, but are typically more expensive than metal plugs. When glow plugs need replacement (an unfortunate necessity of almost all vehicle components), this can be a tricky prospect. Because ceramic plugs are particularly delicate and replacing them can require some awkward maneuvering, diesel owners inexperienced with this task might want to have a professional change their glow plugs. You should also never replace ceramic plugs with metal ones. Fortunately, this shouldn't come up often; the Royal Automotive Club estimates that glow plugs can last up to 100,000 miles. 

An intake heater's function is quite clear from its name. Because diesel engines make use of the heat generated by compressing air, keeping that heat consistent and reliable is the key. Not only does more efficient combustion save you money on fuel, but a pre-heater brings the temperature in the chambers to an optimum level for combustion, reducing polluting white smoke. Intake heaters have electric elements and are mounted in the manifold or air cleaner assembly or in between components. 

The wire or ribbon heating elements in intake heaters are made from alloys of metals like chromium, copper, and nickel. They draw power from the battery, so you'll want to make sure your charging system is working properly before installing a product like the Standard Motor Products DIH1 intake heater for Ram trucks. Installing an intake heater usually only requires the removal and replacement of a few bolts and two gaskets, so this is a job most experienced DIY mechanics can handle.