Diesel Repair

There are several diesel problems that people bring their trucks in for. The main one is when the diesel has a check engine light on. Usually, when people try and diagnose something by themselves when there is a check engine light, that really leads into other problems. Diesel parts are very expensive, and if you are just throwing parts into the truck to try and fix the problem, that is going to get really expensive.

Other common issues include:

• Running Problems: This includes cases where the engine is not giving you the power that you are used to or it is hesitating.
• DEF System Issues: Problems with the diesel exhaust fluid system are very common. These usually require someone who has the proper tooling to be able to diagnose what the problem is.

Typically, when there is a running problem or there is a check engine light of some sort on, that is when you want to go with a professional. You need somebody who has the proper equipment and the proper training to diagnose what is going on with the diesel. The challenge is that when you start throwing parts at a diesel, it gets very expensive fast because the parts in these trucks are pretty expensive. If you do not know specifically what is causing the problem, you might throw several parts in it and it still has the same problem because it was not properly diagnosed.

Problems with your injectors or the fuel system typically start with some kind of a long crank when you are trying to start the vehicle. You might also notice a misfire, or run into power problems where you get a little bit of a hesitation when you put your foot on the gas.

Other warning signs include:

• Black Smoke: This happens because the system is dumping too much fuel into the engine.
• Frequent DPF Regeneration: You may experience too frequent diesel particulate filter regeneration. This happens because too much fuel is being sent into the system, which clogs up that filter and causes it to want to regenerate all the time.

Diesel engines typically blow black smoke when they are on a heavy acceleration. This happens when your foot is in the gas because you want to pass somebody, or you are carrying a heavy load up a hill. This is totally common as you are putting a lot of fuel into the engine.

You should be worried about this when it does not go away after acceleration. If you are not into the gas and it is always blowing black smoke, that tells you that you want to have a professional look at it because that is a deeper problem. This can be caused by problems with the injectors, a fuel system putting too much fuel in, or the engine not getting enough air. This can sometimes be caused by something as simple as a bad air filter.

One of the most common things that causes a diesel engine to overheat is not having enough airflow going through the cooling system. In a diesel, you have the radiator up front and these trucks collect bugs and debris which blocks that airflow.

Other things that can cause overheating include:

• Gelled Coolant: If the cooling system has not been flushed often enough, coolant can get gelled up inside the radiator and prevent proper flow.
• Bad Fan Clutch: The fan clutch regulates how fast the fan spins. If it goes bad, it is not spinning fast enough and is not pulling enough air through the radiator.
• Low Coolant Levels: This could be because of an air pocket in the system after a change, or a slow coolant leak that has reached a point where the radiator is low.

We typically recommend changing the oil between five and seven thousand miles, even though the manufacturer may say that you can go up to ten thousand miles. The problem with diesel engines is that they are often used as work trucks and they idle a lot. If that engine is running, it is not taking miles in the truck, but it is actually using time and hours. Sticking with every 5,000 miles is usually going to protect you for those extra hours that it is sitting with the air conditioning on or performing work on a job site.

If you skip regular maintenance for your filters, one of the first things that you are going to see is lack of power and acceleration.

• Air Filters: A dirty air filter causes air restriction, meaning it is not putting enough air into the system to burn efficiently.
• Fuel Filters: If your fuel filters are dirty, it puts a lot more pressure on the fuel pump to push fuel into those injectors. This can cause premature damage to your fuel injectors from rust, water, and any debris that came from the tank or the pump.

Preventative maintenance is really important because diesel engines are so expensive. These are high performance mechanical engines that need to be taken care of. If you do not take care of them, you may only get 150,000 miles out of the engine, and they cost $30,000 to $40,000 to replace. But if you do the regular maintenance, you can get 300,000 to 500,000 miles out of these things.

The cooling system does not just affect the engine. It also cools the transmission and has everything to do with how cold your AC is blowing. If the engine coolant is too old or does not have the proper mixture, it will boil too fast and will not allow the engine to cool off. By changing that fluid out every 30,000 miles or so, you are going to have fresh coolant that keeps the engine contaminant-free.

• Battery Issue: You will know it is a battery issue if the engine is just not cranking over fast enough. You have to have a lot of RPMs to be able to start a diesel.
• Glow Plug Issue: If it is cranking over really fast and it is not starting in cool weather, that could be a glow plug issue. The engine block is not getting heated up enough to actually ignite that diesel fuel. A red flag is if the truck was starting fine when it was warm out, but now it will not start when it is cool.

The most costly thing you can do is throw parts at a problem rather than getting it properly tested by a professional. This can get very expensive fast because diesel parts are pricey. Another costly repair is when somebody runs gas through their diesel by mistake. If this happens, the tank needs to be drained and you need to put fresh diesel in the system.

The most expensive mistake is putting diesel exhaust fluid (DEF) into the fuel. If that fluid gets poured into the diesel, it crystallizes. If you turn that key on and the fuel pump pumps it into the injectors, you might have to replace everything from the tank up to the fuel injectors. If you make this mistake, you must stop, take the key out, and do not do anything.

The most effective habits are the simple ones recommended by manufacturers, focusing on clean fluids and filters. Key habits include:

Oil Changes: Change your oil every 5,000 to 7,000 miles to keep the engine clean. While some manufacturers suggest longer intervals, regular changes are “cheap insurance” for an engine that can cost $30,000 to $40,000 to replace.

Air Filter Maintenance: In dusty environments like Arizona, air filters should be checked or changed roughly every six months. This protects the turbocharger from compressing sand and debris into the engine.

Fuel Filter Changes: Most diesels require fuel filter replacements every 20,000 to 30,000 miles. This prevents contaminants found in standard pump fuel from clogging or breaking expensive fuel injectors.

Maintenance should generally follow the manufacturer’s schedule for oil, fuel, coolant, and air filter services. However, for diesels used in commercial applications or those that spend a lot of time idling, maintenance should be performed more frequently. In these cases, service intervals are determined by engine “run time” rather than just mileage.

Unlike gasoline, diesel typically only has one grade at the pump. While fuel additives are available, they generally do not change performance significantly. Maximum performance and longevity come from the engine’s technology and ensuring all fluids and filters remain clean.

Clean filters ensure that the air and fuel entering the engine are free of debris, allowing injectors to fire properly and the engine to stay lubricated. This maximizes power and mileage while preventing the “undue wear” that occurs when an engine is forced to suck in dust or run on dirty, acidic oil.

Just like a gas vehicle, “putting your foot in it” or racing from light to light will significantly reduce your mileage. However, modern diesels are so powerful that even with light pressure on the gas, they can achieve between 20 and 30 miles per gallon.

Cooling system care is less about immediate efficiency and more about engine longevity. Over time, antifreeze can become acidic and eat away at rubber and metal components. Regular flushes prevent the coolant from gelling or plugging up the radiator, keeping the engine at an optimum operating temperature.

The best protection during extreme heat or heavy towing is staying ahead of all basic maintenance. A professional should check all fluids and service intervals; if a diesel is up-to-date on maintenance, it can handle heavy loads in high temperatures without issue.

Modern diesels are highly specific regarding the types of antifreeze, transmission fluid, and differential oil they require. Using the wrong grade can cause issues like transmission “chirping” or hesitation. Using the correct, manufacturer-upgraded fluids ensures the vehicle lasts a long time and performs at its peak.

Fleet owners benefit from “professional eyes” that can predict failures before they happen, such as a battery about to go bad. Regular inspections at a repair shop allow technicians to take photos and keep records of potential issues, helping fleet managers avoid costly breakdowns and downtime.

Realistic mileage varies by vehicle type:

• Eco Diesels: Can achieve 25 to 40 miles per gallon with proper maintenance.
• Heavy Duty/Work Trucks: Typically get 15 to 25 miles per gallon, even when carrying heavy commercial loads. With proper preventative maintenance, these engines can realistically last between 300,000 and 500,000 miles.