Diesel Hard to Start After Sitting (Why and What to Do)

You may wake up in the morning and start your car, but your diesel engine has to have a problem getting started. This is a common situation that could have been experienced by any driver at some point in their lives.

As a driver, you might be already aware of how significant and vital the role of weather conditions on the condition and performance of the car. You can always experience some issues with your car in cold weather, and this one is no exemption.

So now, we will learn all about diesel engines. Let us get started.

Diesel Hard to Start After Sitting

What Causes a Diesel to Be Hard to Start?

This is a frustrating situation to be in. Of course, no one would ever want their vehicle not to start.

If your vehicle does not start, you will still have to think of all the possible reasons why it won’t. We will now discuss all the possible reasons why your diesel engine has a hard time starting.

1. You Might Have Issues With Your Fuel Delivery

If you suspect that your car might have issues with your fuel delivery, you can always check them yourself. You need to if the injector timing is correct. You can check this by using a scan tool.

This will help you determine if your injector timing is correct. You also need to check if the fuel has air. If there are any leaks on the fuel lines or the pump gives air into the system, this can most likely be why your engine will die right after it started.

You may also have difficulty in starting the engine again. You also need to check for clogged fuel filters. In every 20,000 to 40,000 miles, your fuel filters must be changed by then. Fuel filters must be checked and replaced as often as necessary.

You can also try to consider the pump. Check for any clicking noise every time you start the engine.

If you do not hear any clicking when you turn the engine on, it can be the fault of the solenoid. However, if there is a click when you turn the engine on, but there is no fuel that is being pushed to the injector lines, maybe it is time already to replace your pump.

2. You Might Have Issues With Your Injectors

Compared to a gasoline engine, the pressure in a diesel injector is very high. But do not worry. The pressure will go down over time.

You need to constantly check if the pressure on your injectors is too high or too low. You need to know that extreme level is not good. Your injectors can be dirty.

If your injectors are dirty, you will probably have white smoke coming out sometimes from your exhaust. You might also notice a rough idle or a loss of power.

On the other hand, if there is any black smoke from your exhaust, you might have a leaky injector. To test if your injectors are bad, you can check the resistance on your glow plugs or check the temperature of the cylinders.

3. You Might Have A Contaminated Fuel

Bacteria love warm temperatures. You should know that diesel is a perfect environment for bacteria. Bacteria love diesel compared to gasoline.

Bacteria will grow more when the temperature is warm. You need to check if there are any contaminations on your fuel. If you notice a coating in your fuel tank in the color green or black, this might be the bacteria accumulating in your fuel tank.

You can also look for sulfuric odor. It would be best if you got rid of this substance at once. You must drain your fuel tank and clean it.

You also need to check for other parts that have been contaminated. You also need to clean these parts. You can add biocide to your fuel tank so that the bacteria cannot penetrate anymore.

sitting diesel engine

How Do You Start a Diesel Engine That Has Been Sitting?

Follow these basic steps on how to start a diesel engine that has been sitting. You need to drain the fuel tank and fill it with new fuel. You also need to change the fuel filter with a new one.

Your engine will crank more quickly if you remove the glow plugs. Put some MMO to the cylinders. After putting some MMO to the cylinders, let it sit overnight.

After that, you need to crack the fuel lines in the injectors. The next day, you need to leak out the line to the injector union. You can do this by cranking the engine until the fuel leaks out.

It would be best if you let all the oil out of the cylinders. Avoid frying the starter by cranking in bursts.

Next is to tighten the fuel lines. Install the glow plugs back, and your diesel engine should be able to start right up.

Related: What Is the Cause of Hard Starting in Diesel Engine?

Is It Bad For a Diesel to Sit?

Not necessarily, but diesel might grow fungi or mold. This is why diesel must be driven around regularly. Diesel can go badly for about thirty days.

Diesel also needs heat. It must be driven around once in a while. The diesel needs to be warm. Though many people would say they encountered no problem with letting their diesel sit, it is best to be safe than sorry.

How Long Can You Let a Diesel Engine Sit?

There are a lot of answers to this. There are many diesel engines that some drivers left to sit for months or even years, and they encountered no severe problem with it. Some drivers would also say not to let your diesel engine sit for too long because you can encounter many issues.

You can try it for yourself, though. You can leave your diesel engine to have some testing on it. You may be able to know the threshold of your engine diesel.


In summary, a diesel engine can be hard to start. This can sometimes be the doing of cold weather.

 In warm temperatures, the bacteria can also penetrate and accumulate in your fuel. Diesel is an ideal environment for fungi and bacteria. You need to consider this if you are planning to let your diesel sit.


Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more