Diesel Engine Hard to Start in the Morning (Causes and Solutions)

Diesel engine hard to start in the morning

‍Have you ever wondered why your diesel engine is hard to start in the morning? Well, we got you covered.

Diesel engines have always been known for their reliability and durability. However, one of the most common issues faced by diesel vehicle owners is the hard start of the engine, especially in the morning or after the vehicle has been sitting idle for an extended period.

This article will discuss the possible reasons behind this problem and provide helpful tips and solutions to make your diesel engine start more easily in the morning.

1. Fuel Pressure Issues

One possible reason for a diesel engine is hard to start in the morning is the fuel pressure in the injector lines bleeding back to the fuel tank while the car sits for long periods.

When this happens, you have to crank the engine over quite a number of times until the pressure is built back up and fuel reaches the injectors.

Check Valves Malfunctioning

There are a couple of one-way check valves in the system that could be malfunctioning.

The mechanical lift pump located at the bottom of the injection pump has a check valve that keeps the pump suction fuel.

There is also a check valve on the side of the injection pump that keeps return fuel from leaking back down into the pump.


Before replacing the pump or the check valve, it is recommended to run two cans of diesel purge through your engine to clean out any gunk buildup.

This could be the reason why the valves are not seating properly. If that does not help, go after the check valve on the side of the pump. Take it off and inspect it.

The last resort would be to replace the lift pump as these are expensive.

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2. Inadequate Fuel Delivery or Pressure

Another common reason for a hard starting diesel engine is inadequate fuel delivery or pressure.

This can be caused by a clogged fuel filter, injectors, or even contaminated or old gasoline.

If you can start the vehicle readily when cold by holding the accelerator pedal to the floor while cranking, suspect an air induction fault such as a stuck idle air control (IAC) valve.

Diagnostics and Repairs

To resolve the issue, consider requesting a hard start diagnostic from a certified mechanic.

They will be able to determine the exact cause of the problem and recommend appropriate repairs.

3. Cold Weather Effects on Diesel Engines

Cold weather can make starting a diesel engine even more challenging. Diesel engines require much higher temperatures to ignite the fuel than gasoline engines, making them harder to start in cold weather.

To combat this issue, various heating devices have been developed to keep different parts of the vehicle warm when it is not being driven.

Glow Plugs and Block Heaters

Glow plugs work by heating the internal combustion chamber, allowing for suitable conditions for compression and ignition.

Block heaters are another option, which are built-in electric-powered heaters that keep the engine block warm overnight.

Both of these devices can be extremely helpful in getting a diesel engine started in cold weather.

Waiting on the Glow Plugs

It is important to wait for the glow plugs to heat the combustion chamber properly before attempting to start the engine.

Cold fuel sprayed on semi-heated plugs can cause the diesel fuel to get up and stick to the cylinder heads, potentially causing damage.

Installing a Second Battery

Since glow plugs require a significant amount of power from your vehicle’s battery, it is a good idea to have a fully charged battery or a secondary battery installed just for the glow plugs.

This will ensure that the glow plugs have enough power to do their job, even in cold temperatures.

4. Regular Oil Changes and Proper Oil Selection

An engine is roughly 2-3 times harder to start at 0 degrees Fahrenheit due to thicker oil lubricating the hard internal parts of the engine.

Thicker oil creates more resistance on the bearings and moving parts, making it more difficult for the engine to start.

Regular oil changes and using the proper type of oil for your diesel engine can help maintain proper lubrication and make starting easier in cold weather.

Synthetic vs. Natural Mineral Oils

Both synthetic and natural mineral oils are suitable for diesel engines. However, it is important to change the oil regularly, especially in colder climates, to ensure that the oil remains fresh and maintains its proper viscosity.

Oil Oxidation and Engine Sludge

When oil oxidizes, it begins to break down chemically, leading to the formation of black engine sludge.

This sludge can eventually destroy a diesel engine if not properly cleaned and maintained.

Regular oil changes help to prevent this from happening.

5. Turning Off Non-Essential Accessories

Remember that you only have so much battery power available on a cold winter’s day.

Limit the use of headlights, radios, phone chargers, heaters, and air conditioners while starting the engine to ensure that your glow plugs receive the necessary power to function properly.

6. Using the Correct Diesel Fuel

Diesel fuel comes in two different grades: Diesel #1D and Diesel #2D. Diesel #2D is the most widely used diesel fuel and is recommended for normal driving conditions.

However, Diesel #1D is recommended for use in cold weather climates, as it is thinner and flows more easily within the engine, making it less likely to become thicker or sludge-like in freezing temperatures.

Blended Diesel Fuels

Many gas stations offer a blended Diesel #1 and Diesel #2 option during the winter months.

This can help to ensure that your diesel engine starts more easily in cold weather conditions.

7. Including Winter Fuel Additives

Winter blend diesel fuel additives can be added to your diesel fuel to help improve its performance in cold weather.

These additives work by lowering the Cold Filter Plugging Point (CFPP), which is a standardized test to determine the rate at which diesel fuel will flow through a filtration device under cooler conditions.

Mixing Additives During Fueling

It is important to add these additives directly after filling your vehicle with Diesel #1D at a service station on a cold day.

This will ensure that the additives have time to mix with the fuel at warmer temperatures, providing the best results.

8. Avoiding Mixing Additives with Winterized Diesel Fuel

It is essential not to mix additives with winterized diesel fuel, as the incompatibilities between multiple types of additives may deteriorate the fluids in the fuel blend and completely reverse any benefits.

Stick to either using winterized diesel fuel or adding your own additives, but not both.

9. Changing the Fuel Filter if Fuel Has Gelled

If you suspect that your diesel fuel has gelled, it is important to change the fuel filter immediately.

The gel in the fuel filter can block the flow of fuel from the tank to the injector pump, causing the engine to struggle to start.

10. Storing Your Diesel Vehicle in a Heated Location

Storing your diesel vehicle in a heated location, such as a garage or barn, can help to keep the engine and its components warmer, making it easier to start in the morning.

If possible, use a block heater on a timer to warm up the engine before attempting to start it.

11. Allowing the Engine to Warm Up Before Driving

It is advisable to give the engine 5-10 minutes to achieve proper operating temperature before driving.

This will allow the oil temperature to reach optimal levels and lubricate the engine properly, reducing the risk of damage from cold starting.

12. Proper Maintenance and Regular Checkups

Ensuring that your diesel engine is well-maintained and regularly checked by a certified mechanic can help to prevent hard starting issues in the long run.

By addressing any issues as they arise and keeping your engine in top condition, you can enjoy a more reliable and easier-to-start diesel vehicle.

Hard Start Problem. diesel timing >> Check out the video below:


In conclusion, diesel engines can be hard to start in the morning or after sitting idle for long periods due to various factors such as fuel pressure issues, inadequate fuel delivery or pressure, cold weather effects, and improper maintenance.

By following the tips and solutions discussed in this article, you can improve the starting performance of your diesel engine and enjoy a smoother morning drive.

Stephan K.

I have been working as a mechanic for over 13 years and have been deeper into advanced automotive diagnostics for some years.

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