Grid Heaters Explained: How Cummins Diesels Start Without Glow Plugs
The Cummins 5.9L and 6.7L use an intake grid heater instead of glow plugs. How it works, the wait-to-start cycle, why it punishes batteries, and the truth about deletes.
How a grid heater works
Most diesels warm each cylinder with glow plugs. Ram's Cummins engines — and many medium-duty trucks — instead mount one electric grid in the intake tract, like a toaster element the incoming air must pass through. Key the ignition at cold temperatures and the wait-to-start light holds while the grid pulls a very large current for several seconds, heating the intake air so the cylinders can reach ignition temperature on the first revolutions. After start-up, the grid cycles on and off during warm-up to keep combustion clean and white smoke down.
One grid instead of six plugs means fewer failure points and nothing threaded into the head — a big part of the Cummins cold-reliability reputation. The trade: that single element draws roughly 100–200 amps, which is a brutal load on cold batteries.
Living with one in a Canadian winter
Respect the wait-to-start light — cranking before it goes out means cranking an unheated engine. Below about -15°C, expect the post-start grid cycling to dim the lights periodically; that's normal. Because the grid leans so hard on the batteries, the standard Cummins winter stack is: both batteries load-tested each fall and replaced as a pair, battery blankets on both, and the factory block heater on a timer. A plugged-in Cummins often starts with minimal grid heating at all — the block heater effectively does the grid's job in advance, which is exactly why Canadian trucks ship with one.
The delete question, honestly
Grid heater deletes are popular in the performance world for a marginal airflow gain, and on the 6.7L because a specific failure — the heater's electrical nut backing off and getting swallowed by a cylinder — has damaged engines often enough to spawn billet replacement parts. The honest Canadian answer: if the truck lives anywhere with real winter, deleting cold-start hardware costs you every January morning for a dyno-invisible gain. The engineering fix for the 6.7L nut issue is an upgraded aftermarket grid or intake horn that keeps heating function, not a block-off plate. Trucks that never see frost can make their own call.
FAQ
Does a Cummins have glow plugs?
No — Cummins diesels use an intake grid heater: one high-current electric element that heats incoming air for all six cylinders. The wait-to-start light is the grid doing its job before cranking.
Why do my lights dim after starting my Cummins in the cold?
The grid heater cycles on and off during warm-up, and each cycle draws 100+ amps. Periodic dimming below about -15°C is normal. Constant dimming or hard starts usually mean the batteries are due — test both, replace as a pair.
Does a block heater replace the grid heater?
It complements it. The grid heats intake air at start; the block heater pre-warms the whole engine so the grid barely has to work. A plugged-in Cummins starts faster, cycles the grid less and spares the batteries — the standard cold-country setup is both, plus battery blankets.
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