Glow plugs are used to preheat the diesel engine so that it can be started immediately in cold conditions. If you have trouble starting the engine or you see smoke coming out of the exhaust, it could be that one of the glow plugs in your engine is faulty. You can test glow plugs yourself without having to visit a repair shop or mechanic.
Step
Method 1 of 3: Testing the glow plug in the engine
Step 1. Use a multimeter
A multimeter is a black box containing an electronic circuit that is used to check electrical circuits or equipment. The multimeter has a large knob in the center that you can use to adjust. The multimeter has black (negative) and red (positive) wires to check current and resistance. These cables usually have a metal clamp at the end. Although the multimeter may seem confusing with all the numbers and dials, you only need to use one setting to perform this test.
Better yet, use a digital multimeter to perform this test. The digital multimeter has a display that shows the number of test results. Analog multimeters are more difficult to read because they use needles and the numbers are stacked
Step 2. Set the multimeter to Ohms
The Ohm suit is indicated by a symbol that resembles an inverted horseshoe. There are two long vertical lines indicating the Ohm range.
Step 3. Find the resistance of your multimeter
Touch both ends of the black and red wires, and record the number of results. Make sure the two metal clamps are touching each other. If you are using a digital multimeter, the resulting number will be shown on the screen.
Subtract this number later with the reading from the glow plug
Step 4. Test battery voltage
Set your multimeter to Volt reading mode. Connect the black wire of the multimeter to the negative terminal of the battery, and the red wire to the positive terminal of the battery. The number that is read should be close to 12.5 Volts when the car engine is off and close to 13 Volts when the car engine is on.
If the numbers are different, check the battery and alternator first before proceeding. The glow plug will not work properly if it does not receive the proper voltage
Step 5. Locate the glow plug
Refer to your car's manual to find out where the glow plugs are in the car's engine. The location may vary according to the make and model of your vehicle.
Step 6. Unscrew the glow plug or plug
Usually there is a cover that protects the glow plug. Open the cover to allow the multimeter clamp to reach the glow plug.
Check connectors and pins for signs of corrosion. Take this opportunity to clean it up at once
Step 7. Clamp the negative wire of the multimeter to the ground point of the machine
The two main ground points can be found by tracing the wires coming from the battery and going to the engine wall. This cable will be plugged with bolts. Clamp the multimeter negative wire on one of these screws as ground.
Read your car's manual to find out the exact location of the ground points
Step 8. Connect the positive wire of the multimeter to the top end of the glow plug
If the negative wire of the multimeter is still connected to the negative terminal of the battery, leave it alone, no need to move it
Step 9. Observe the multimeter screen
The resulting number from the reading of this electrical resistance should be in the range of 0.6 to 2 Ohms.
- Subtract the resulting resistance number by the resistance of the multimeter itself. For example, if the resistance of a glow plug reads 0.9 Ohm while the multimeter resistance is 0.2 Ohm, then the actual value is 0.7 Ohm.
- All the glow plugs in your engine should have the same number. A glow plug with a greater resistance can affect your engine's performance, even if the glow plug itself is still in good condition.
Step 10. Replace glow plugs
If one or more glow plugs have a problem, replace them entirely. Never replace just one spark plug.
Method 2 of 3: Testing Removed Spark Plugs
Step 1. Remove the glow plug from the engine
Read your car's manual to find out where the glow plugs are and the best way to remove them. The location and method may vary according to the make and model of your vehicle.
Step 2. Set the multimeter to Ohm mode
Set the range between 200-1000 Ohm. If the number obtained from the glow plug is much higher than the multimeter setting, then the glow plug is faulty.
Step 3. Know the resistance value of the multimeter
Cross the two multimeter wires with each other and record the resulting number.
Subtract this number later with the number obtained from the glow plug reading
Step 4. Touch the multimeter negative wire to the nut on the glow plug
Do not touch the negative wire higher than the nut.
Step 5. Touch the positive wire of the multimeter to the tip of the glow plug
The tip of the glow plug will be visible when you open the cap.
Step 6. View the readings of the multimeter
The resistance value of the glow plug must be between 0, 1 and 2 Ohms.
- Subtract the resistance number of your multimeter by the resistance value obtained from the glow plug. For example, if the resistance of a glow plug reads 0.9 Ohm and the multimeter resistance is 0.2 Ohm, then the actual resistance is 0.7 Ohm.
- All the glow plugs in your engine should have the same number. A glow plug with a greater resistance can affect the performance of your engine, even if the glow plug itself is still in good condition.
Step 7. Replace glow plugs
If one or more glow plugs have a problem, replace them entirely. Never replace just one spark plug.
Method 3 of 3: Testing With a Battery Charger
Step 1. Remove the glow plug from the engine
Read your car's manual to find out where the glow plugs are and the best way to remove them. The location and method may vary according to the make and model of your vehicle.
Step 2. Use a 10-12 Ampere battery charger
Using a charger with this range can provide sufficient current to heat the glow plug and avoid false negative readings.
Step 3. Attach the negative wire from the charger to the glow plug body
Attach the negative clamp from the charger to the glow plug body.
Step 4. Plug in the positive cable from the charger
Attach the positive clamp from the charger to the tip of the glow plug.
Step 5. Observe if the spark plug glows
If the spark plug doesn't glow within a few seconds, the spark plug is faulty.
- Do not leave the glow plug connected to the charger for an excessive amount of time, as this will damage a good glow plug.
- It's possible that the spark plug will still glow, but fail to warm up your engine.
Step 6. Replace glow plugs
If one or more of the glow plugs have a problem, replace them entirely. Never replace just one spark plug.
Tips
- Remove the glow plug when the engine is hot. It is more difficult to remove glow plugs when the engine is cold.
- Test all new glow plugs before you install them on your engine.
- Always wear safety glasses when working near your car.
