Where are the glow plugs on a 5.9 Cummins?
The glow plugs in a 5.9 Cummins are six in total, one for each cylinder, and they live in the cylinder head to heat the air for starting in cold weather.
Location and design overview
In the 5.9 Cummins, glow plugs are mounted in the cylinder head, with one plug per cylinder. They heat the air in the pre‑combustion chamber on the older indirect-injection designs (IDI) and the combustion chamber on the later direct-injection designs (DI). The plugs are accessed from the top of the engine, typically behind or beneath the valve covers. Replacing them requires careful handling to avoid breaking a stubborn plug and to ensure the electrical harness is reconnected properly.
Before you inspect or replace glow plugs, here are the key facts to know about their arrangement and access:
- There are six glow plugs total, one for each cylinder.
- They are installed in the cylinder head, not inside the valve cover.
- Access to all plugs is from the top of the engine; you may need to remove the valve covers or shielding to reach some plugs.
- Replacement requires a suitable glow-plug socket and careful threading to avoid cross-threading or breakage.
- Typical symptoms of failing glow plugs include hard starting in cold weather, rough idle, reduced power on startup, and sometimes white smoke during startup.
Concluding note: If you’re unsure about which variant you have (IDI vs. DI) or how to service the plugs, consult the service manual for your specific year/model or contact a Cummins-certified technician.
Practical guidance for locating and replacing glow plugs
For those tackling a DIY glow-plug job, follow these general steps to locate and replace the plugs on a 5.9 Cummins:
- Disconnect the battery to prevent any accidental electrical shorts.
- Remove the valve covers or any shielding that blocks access to the head’s top surface.
- Identify the six glow-plug terminals in the head, each corresponding to a cylinder.
- Carefully disconnect the wiring harness from each glow plug, noting their arrangement for correct reassembly.
- Using a proper glow-plug socket, back out the old plug slowly. If a plug is stuck, apply penetrating oil and give extra time before attempting removal again.
- Install the new glow plugs with the correct orientation and thread them in by hand first to avoid cross-threading; snug them to the manufacturer’s specification.
- Reconnect the wiring harness, replace valve covers/shielding, reconnect the battery, and perform a cold-start test to confirm proper operation.
Concluding paragraph: Proper replacement helps ensure reliable cold starts and avoids cross-thread damage to the head. If any plug remains stubborn, consider professional service to prevent head damage.
Common symptoms and diagnostic notes
Diagnosing glow-plug issues typically starts with cold-start behavior. Look for:
- Difficulty starting in cold weather or longer cranking times
- Rough running or misfires after start-up
- Excess white or blue smoke on startup that clears after a few seconds
- Check-engine-light or glow-plug indicator warning (depending on model/year)
Concluding paragraph: If symptoms persist after replacing suspected plugs, further diagnostics may be needed to check the glow-plug relay, wiring harness, and the engine-control system.
Summary
The 5.9 Cummins uses six glow plugs, one for each cylinder, located in the cylinder head. They heat the air for cold starts in both the older indirect-injection and newer direct-injection variants. Access is from the top of the engine behind the valve covers, and replacement requires care to avoid breaking the plugs and to ensure proper electrical connections. Understanding their location helps with diagnosis, maintenance, and reliable winter starts.
Where are glow plugs located?
Glow plugs are located in each cylinder of a diesel engine, inside the combustion chamber or pre-chamber. They are typically found on the top of the cylinder head and are accessible after removing the glow plug wires and any covers that obstruct them.
You can watch this video to see the location of glow plugs in an engine: 58sSiRobbYouTube · Apr 11, 2019
- Location: One glow plug is installed in each cylinder.
- Position: They are screwed into the cylinder head and protrude into the combustion chamber.
- Accessibility: You will need to remove the glow plug wires and possibly the intake manifold or other components to get to them.
This video shows a mechanic demonstrating how to remove glow plugs from an engine: 59sDriveway DemonsYouTube · Mar 5, 2022
What is the biggest problem with the 5.9 Cummins?
Common 5.9L Cummins Engine Problems
- Gear Case Leaks & Dowel Pin Problems.
- Fuel System Failures.
- Cylinder Head Gasket Leaks.
- Water Pump Failure.
- #53 Engine Block Cracks (Selective Years)
- Heater Grid Bolt Failures.
- Transmission Wear.
- Design Simplicity vs.
How many glow plugs are in a 5.9 Cummins?
Cummins diesel engines do not have spark plugs, as diesel engines use compression ignition rather than spark ignition. Do Dodge Cummins have glow plugs? Dodge trucks equipped with Cummins diesel engines use grid heaters instead of glow plugs for cold weather starting.
Does a Cummins diesel have glow plugs?
Since 2007, Cummins-powered Ram Heavy Duty trucks have relied on a grid heater system for cold starts, unlike their competitors, which have long used glow plugs. That changes for 2025, as Ram and Cummins have officially switched to glow plugs in their newest version of the turbodiesel 6.7-liter Cummins I6 engine.
