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Diesel Tractor Won’t Start: Troubleshooting Guide

Diesel Tractor Won’t Start: Troubleshooting Guide

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Paul Brown

Diesel engines are considered more reliable than gasoline engines, as they have considerably fewer parts that can potentially fail. That doesn’t mean, however, that you won’t run into issues with your diesel tractor.

If your diesel tractor won’t start, the first place to look is the fuel filter. The filter may be dirty, which clogs the vents and won’t allow fuel to travel to the engine from the fuel tank. Remove and clean the fuel filter, or replace it altogether. This will likely solve your problem.

If this doesn’t solve your problem, there are other reasons why your tractor may not be starting. In this troubleshooting guide, we will walk through the step-by-step instructions for determining what may be happening with your tractor, and how to fix it.

How Diesel Engines Work

Before we attempt to fix a diesel engine, we should briefly overview how they work.

A diesel engine is an internal combustion engine. That means that it creates a force by igniting fuel internally. The diesel fuel of a diesel engine actually lights on fire inside the engine to create the energy needed to propel your tractor.

This combustion happens in four steps:

  1. Intake: This is where the air is first allowed to enter the cylinders. Inside the cylinders is where the combustion occurs.
  2. Compression: The air in the cylinders needs to be compressed and heated to a point that is so hot, that when the fuel is introduced to the air, it will ignite immediately.
  3. Ignition: The diesel fuel is injected into the cylinders by the injection rod. It is delivered in an even spray to the cylinders, where it ignites immediately. This creates the energy to cause the tractor to move.
  4. Exhaust: When the fuel ignites, it creates fumes from the reaction. This needs to be vented into the air, or the engine will crack from the pressure. In a diesel engine, this exhaust sometimes contains soot particles, which is why it is often black.

One of the great things about diesel engines is that they have no carburetor or spark plugs. These are used in gasoline engines to premix and ignite fuel and air in the cylinders.

We can safely rule out that your diesel tractor’s issues have nothing to do with those parts.

Why Isn’t My Diesel Engine Starting

Now that we know how a diesel engine works, we can look at some of the potential reasons your diesel engine may not be starting.

  • A dead battery
  • Clogged fuel filter or fuel lines
  • Damaged or broken mechanical parts
  • Overheating engine
  • Contaminated diesel fuel
  • Jammed fuel injection pump
  • Empty fuel tank
  • Cold outdoor temperatures
  • Air in the fuel lines or fuel

Step By Step Guide to Determining Why Your Diesel Tractor Won’t Start

As listed above, there are many reasons why your diesel tractor may not be starting. We will examine them in order of most to least likely.

Check Your Fuel Filter

Of all of the issues that cause a diesel engine not to start, this one seems to top the list. Remove your fuel filter and examine it. If it is dirty, it may be fully clogged, and not allowing fuel to get through to the engine.

Clean or replace the fuel filter, and try starting your tractor again.

Also, be sure to check your fuel lines. If these are clogged, they can cause the same issues as a dirty fuel filter.

Test Your Battery

If your tractor won’t start, your battery may be dead. You may hear a small click when you try and start the tractor or nothing that all. If you do, read this specific guide for a diesel engine clicking but not turning over.

If you suspect the battery you can try cleaning the posts. Remove the NEGATIVE (-) attachment first, then the POSITIVE (+) (source). Clean the posts with something abrasive, like a mixture of water and baking soda. Completely dry the terminals before reattaching the cables. Be sure to attach the POSITIVE (+) first, and then the NEGATIVE (-). 

If this doesn’t work, your battery may be completely dead. Look for leaking, swelling, or bloating of your battery case. Any of these signifies the end of your battery’s life.

This video from YouTube is a great resource for determining whether the problem is actually the battery or the alternator:

How To Test a Failed Battery or Alternator ✔

You can also take your battery to a mechanic, and they can test it for life. Many mechanics offer this service for free, so take advantage of it before investing in a new battery.

Fill Your Fuel Tank

While it may seem too obvious, it is possible you ran out of fuel. Check your fuel tank to see the level of fuel inside. If you did run out of fuel and refilled your tank, but the tractor still won’t start, you may be encountering another issue.

It is commonly known that once a diesel engine runs out of fuel, you cannot simply refill the tank and start again. The engine requires the fuel to be primed and pressurized. This means that you need to manually prime the engine with fuel before it will run again.

This involves removing the air from the fuel lines with the built-in fuel primer pump on the engine.

Usually, the process looks like this:

  1. Locate the fuel primer pump and bleed screw.
  2. Loosen the bleed screw to allow the air in the fuel lines somewhere to go.
  3. Pump the fuel primer for 5-10 minutes to dispel the air in the lines, and repressurize the fuel.
  4. Keep pumping until you see fuel come out of the bleed screw.
  5. Tighten the bleed screw and replace the fuel pump.
  6. Attempt to start the engine.
  7. If the engine doesn’t start after 10 – 15 seconds, repeat the process above.

These are the basic steps but watch this short YouTube video for a visual demonstration for a more complete walkthrough of the entire process:

BEST way to bleed diesel fuel system (step-by-step)

Cool the Engine

Another common issue of diesel engines not starting is that parts of the engine are overheating. To determine if this is your issue, follow these steps.

  1. Check your coolant. The simplest reason for overheating is a lack of coolant. Wait until the engine cools, then, remove the radiator cap and check your coolant levels. If low, top up the coolant with the same type that is in the radiator or replace it altogether.
  2. Inspect radiator fins for dirt. Dirty radiator fins won’t allow enough air through to cool the engine. To clean these, wait until the engine cools and then use an air compressor to blow dirt off the fins. Be sure not to bend the metal pieces.
  3. Engine thermometer is malfunctioning. Your thermometer may be reading a false temperature, causing your engine to shut down prematurely. To test your thermometer, remove it from the machine and use it to measure boiling water on your stove.
  4. Check your radiator hoses for damage. The hoses running from your radiator to your engine can deteriorate over time. If there are no holes that can be seen with the naked eye, that doesn’t mean that there aren’t much smaller holes causing the problem. A professional should be brought in to diagnose this issue.
  5. Test water pump and cooling fan. If either of these fails, they will cause your engine to overheat, and prevent it from running.

Check Your Fuel for Contamination

Another reason your engine may not be starting is that your diesel fuel is contaminated. If it does start, it’s a common cause of stalling out.

First, smell the fuel in your tank to make sure it does not have any traces of gasoline. If it does, flush the tank immediately and refill with diesel fuel.

Next, check your stored diesel fuel. As diesel fuel ages, it gets contaminated by microbes, usually introduced to it through water, that grow into bacteria and fungi. This can prevent your tractor from starting as well.

How to Avoid Diesel Fuel Contamination 🔧

Consider The Outdoor Temperature

Diesel engines are notoriously hard to start in the cold. Lower temperatures bring a host of issues to diesel engines, including affecting fuel, oil, and parts (source).

Once temperatures lower, engine oil can thicken and can cause drag on the engine. It may cause so much drag that the engine cannot create enough compression in the cylinders to ignite the fuel, meaning it won’t start.

To diagnose this, check the dipstick for globby, gunky oil. You maybe need an oil change with a winterized oil to get things going again.

The cold can also affect your battery. It lowers the battery output, meaning there are fewer amps available to power the engine. This engine will likely need a jumpstart to get it going.

Diesel fuel is also affected by cold temperatures. When temperatures reach 40°F (4.4°C) or below, the hydrocarbons in summer grade diesel fuel begin to turn to wax.

These wax crystals can be created in the water/fuel separator, causing blockages. To solve this, you’ll need to move the tractor to a warm garage so the fuel can be brought up to temperature, and the crystals dissolved.

Check for Air in the Fuel Lines

Diesel engines require three things to run; fuel, air, and compression (or heat). If your fuel lines have air in them, the engine won’t be able to pressurize properly and will prevent the flow of fuel from getting to the engine.

You may have to bleed these lines to get them properly functioning again. To bleed the air from a diesel fuel system, follow these steps:

  1. Turn off the fuel valve.
  2. Clean the external housing of the fuel filter.
  3. Install a new fuel element and gaskets. Add oil to the gaskets to ensure a secure seal.
  4. Open the bleed plug closest to the fuel tank.
  5. Open the fuel supply valve fully, so the fuel can move through the system.
  6. Locate the fuel prime pump usually attached to the machine. 
  7. Pump this for 5-10 minutes, until fuel without bubbles comes out of the bleed plug.
  8. Close this bleed plug, and move onto the next plug closest to the fuel tank. 
  9. Continue through all bleed plugs in the system.
  10. Close all bleed plugs securely.
  11. Attempt to start the engine.
  12. If the engine doesn’t start, retry steps 1-11.

Examine Fuel Injection Pump

As we saw at the beginning of this article, the fuel injection pump plays a crucial role in the diesel engine system.

If the pump is stuck in either the open or closed position, it either won’t deliver fuel or will be blocking the engine from accessing airflow. Either of these will prevent your engine from starting. If it does start, it’ll likely stall out or lose power when under load or going uphill.

If the issue is with your fuel injection pump, you are best bringing your machine to a professional mechanic. The fuel injection is a difficult part to work on at home. It could cost you more, in the long run, to attempt to fix it yourself.

Still, if you want to see what rebuilding one of these looks like, this YouTube video is very informative:

How a Diesel Injector Pump works CAV DPA Build Part 1

Other Reasons Your Tractor Isn’t Starting

If you’ve run through this entire guide and still haven’t figured out why your tractor isn’t starting, you may have one of the following issues.

A Mechanical Part is Damaged Beyond Repair

There is the chance that part of your engine is simply broken. There is no quick fix for something like this, you will have to take it to a professional mechanic, or order the new part yourself if you can identify the issue.

Glow Plugs

Glow plugs are used to aid in the starting of diesel engines in cold weather (source). These glow plugs are placed in the pre-chamber in a pre-chambered diesel engine, while direct injection engines have glow plugs in the combustion chamber.

These little devices have filaments that heat up, which helps the air in the cylinders of a diesel engine reach a high enough temperature to combust the diesel fuel when it enters the chambers.

There can be as many as 10 glow plugs in your diesel engine. Usually, if one fails, you won’t notice a difference in the performance of your tractor. If, however, two or three of these fails, you may notice your tractor is much more difficult to start, if it will start at all.

To find out if your glow plugs are still working, follow these steps:

  1. Leave the glow plugs installed in the engine
  2. Disconnect the wire leading to each glow plug
  3. Connect a test light, like this Innova Circuit Tester (link to Amazon), to the POSITIVE (+) terminal on your battery
  4. Touch the end of the test light to the wire of each glow plug
  5. If the test light glows, the plugs are okay, if it stays dark, those plugs need to be replaced

Your Fuel Cap is Creating a Vacuum in the Engine

tractor won't rev up? Check the fuel!

When an engine runs, the diesel is delivered the engine by the fuel pump, through the fuel lines and fuel filter, to the cylinders. The combustion in the cylinders then creates fumes that are expelled through the exhaust of the tractor.

The pulling of this gas from the fuel tank to the cylinders creates a small vacuum; an amount of pressure in the fuel tank.

As diesel leaves the fuel tank, the tank is under pressure from the substance inside of it leaving. This needs to be replaced with either more fuel or air to keep the pressure inside equalized. Even if your tractor starts, it’ll run rough and smoke if the air to fuel ratio is not in balance.

In the past, the cap for a diesel fuel tank had an open hole with a baffle, or screen, to allow air to enter the tank while keeping dirt and debris out.

Today, our diesel fuel tank caps do the same thing, just in a more sophisticated fashion. Diesel fuel caps have vents in them to allow the air in, which equalizes the pressure in the fuel tank.

These vents are small and nearly impossible for dirt and debris to get through them to the tank.

They can, however, become clogged from dirt in the air. When clogged enough, the vents will be blocked, and the air will not be able to get into the fuel tank. If air cannot replace the fuel leaving the tank, the fuel lines cannot deliver the fuel to the engine.

This is called creating a “vacuum” in the engine. It will prevent your tractor from starting.

To fix this, you can try to clean the fuel cap, though you are probably better off replacing it altogether. If you replace the fuel cap, be sure to purchase a diesel fuel cap with the vents, not a gas cap. Most gas caps do not have vents in them, and your problem will only persist.

When to Call a Professional

If you have gone through this article, and you haven’t solved the issue of your diesel tractor not starting, it is probably time to call a professional. A professional mechanic, while expensive, can likely determine the root of the issue in less time than you ever could.

Another general rule to follow is if you’re at all nervous about working on large machinery, call a professional.


There can be many reasons why your diesel tractor won’t start. A lot of them are simple fixes, like dirty filters, which only require cleaning, while some, like a broken fuel injector pump, are complicated and require professional mechanical attention.

Let’s review some of the reasons why your diesel tractor may not be starting:

  • Clogged fuel filter or fuel lines
  • A dead, weak, or cold battery
  • Empty fuel tank
  • Low outdoor temperature
  • Air in the fuel lines
  • Damaged or stuck fuel injection pump
  • Broken mechanical parts
  • Faulty glow plugs
  • Fuel cap creating a vacuum

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