9 Worst Things You Can Do to a Diesel Engine

[DarkBlack]

2-stroke gas-oil mixture generally are in to 40:1 - 50:1

Fixed it.

 

[Shawn T. W.]

Diesels generally are in to 40:1 - 50:1 compression ratio

Do the mfg's know that? I bet you that would be BIG news to them!!

SR

OK, I was off a bit (more than double!) but I did add the disclaimer of "IIRC"! But a diesel is still nearly double that of a gasser!

However I did get the compression psi correct

Glad I'm not perfect, what a boring life that would be!

 

[dodge man]

Diesels generally are in to 40:1 - 50:1 compression ratio, and well over 400 psi in a compression check ... IIRC ...

There is a reason there is a hefty upcharge for a diesel engine in a pickup truck over the standard gasser ... They cost more to make!

I was going to call you out on those numbers but someone beat me to it.

 

[Shawn T. W.]

I was going to call you out on those numbers but someone beat me to it.

Get with the program, are you awake yet?

(I already acknowledged I was wrong ...) I WAS right on the PSI, and that the fake intelligence info that gassers were built tougher because they were under more pressure was a bunch of bulloney ...

 

[howardjohn]

With starting fluid I was always told to crank the engine over as you spray the starting fluid if possible this way there is diesel fluid in the cylinder not just starting fluid. A mechanic suggested that to me a long time ago.

 

[Texasmark]

9 Worst Things You Can Do to a Diesel Engine

• Letting the fuel tank run low. ...
• not keeping up with oil changes. ...
• Using the wrong type of fuel. ...
• Cold starts without proper warm-up. ...
• Overloading the engine. ...
• Skipping coolant changes. ...
• Neglecting filter maintenance. ...
• Ignoring warning lights. ...
• Failing to keep the engine clean.

FWIW: the following came from a diesel tech course put out by UTI earlier this year. Part of their 45 week diesel training course


Not keeping up with oil changes
Skipping oil changes is one of the fastest ways to wear down your diesel engine. Over time, engine oil loses its lubricity as it breaks down from heat, pressure and contamination. As the oil ages, it becomes less effective at reducing friction, absorbing heat and suspending harmful particles. In diesel engines, where internal pressures and operating temperatures are often higher than in gas engines, this breakdown happens even faster.

Contaminants like soot, fuel dilution and metal particles can accelerate wear on vital components such as bearings, pistons and turbochargers. Sticking to a regular oil change schedule based on your engine’s workload and manufacturer guidelines is essential to maintaining performance, preventing costly damage and extending the life of your diesel engine.

Letting the fuel tank run low
Running a diesel engine on a near-empty tank can cause serious problems. Sediment and contaminants naturally settle at the bottom of the tank, and when fuel levels drop, these particles can be pulled into the fuel system, clogging filters, damaging injectors and reducing fuel flow.

But the bigger concern is air entering the fuel system. Diesel systems rely on consistent pressure and flow, and introducing air can lead to hard starts, engine misfires and, in some cases, injector damage due to improper lubrication and cooling.

Low fuel levels can also increase the risk of moisture buildup, especially in environments with temperature swings. The more space in the tank, the more room for condensation to form, which can lead to microbial growth and fuel degradation. To prevent these issues, it’s best to keep your diesel tank at least a quarter full whenever possible.

Using the wrong type of fuel
Diesel engines require diesel fuel, plain and simple. Accidentally using gasoline in a diesel engine can cause severe damage. Gasoline lacks the lubricating properties that diesel fuel provides, which are essential for protecting high-pressure components like fuel injectors and the fuel pump. Without proper lubrication, these parts can quickly overheat, seize or wear prematurely.

In addition, gasoline combusts differently than diesel. It can ignite too early in the combustion cycle, causing engine knocking, misfires and potentially catastrophic damage to pistons and valves. Even a small amount of gasoline can disrupt the entire fuel system and may require a full flush to prevent long-term issues.

Using the wrong grade of diesel (e.g., #1 vs. #2, or off-road vs. on-road diesel) can also impact engine performance and emissions compliance. Always double-check the pump before refueling and make sure you understand which fuel type your vehicle or equipment requires based on climate, application and manufacturer recommendations.

Cold starts without proper warm-up
Diesel engines don’t respond well to cold starts, especially in freezing temperatures. Starting the engine without allowing it to warm up can cause incomplete combustion, rough idling and excessive engine wear. Cold temperatures thicken both diesel fuel and engine oil, making them harder to circulate through the engine. Thickened oil struggles to reach critical components quickly, increasing friction and wear during those first few moments after startup.

Diesel fuel can also gel in extremely low temperatures, restricting flow to the injectors and fuel pump, which may lead to hard starts or stalling. This is especially problematic without the right winter blend or fuel additives.

To protect your engine, use block heaters, glow plugs or intake heaters to warm the engine and fuel system before starting. Letting the engine idle for a few minutes gives oil time to circulate and ensures the fuel reaches the right temperature for proper combustion, reducing stress and wear on internal parts.

Overloading the engine
Pushing your diesel engine beyond its limits by hauling loads heavier than it’s rated for can cause excessive stress and long-term damage. Overloading increases engine workload, leading to higher operating temperatures, reduced fuel efficiency and accelerated wear on critical components.

When the engine is forced to work harder than intended, internal components like pistons, bearings and valves experience more friction and pressure, which shortens their lifespan. The added strain can also affect the transmission, drivetrain, suspension and braking systems, putting your entire vehicle at risk.

Prolonged overloading can even lead to thermal breakdown of engine oil, decreasing its effectiveness and further compounding wear. To ensure safe and efficient operation, always stick to your vehicle’s recommended weight limits, including the gross vehicle weight rating (GVWR) and tow rating, and evenly distribute loads to avoid unnecessary stress on the engine and chassis.

Skipping coolant changes
Coolant helps regulate engine temperature and prevent internal corrosion, making it critical for diesel engine health. Skipping coolant flushes allows the coolant to degrade over time, reducing its effectiveness and exposing the cooling system to serious risks.

When coolant breaks down, it loses its anti-corrosion properties and can become acidic, leading to rust, scale buildup and clogged coolant passages. This restricts flow and reduces heat transfer, causing the engine to overheat. Degraded coolant can also damage the water pump, radiator and head gasket, potentially resulting in costly repairs.

Signs of bad or failing coolant include:

• Rusty, sludgy or discolored coolant
• Persistent overheating
• Coolant leaks or low levels
• Sweet smell under the hood (indicative of a leak)

Regularly flushing and replacing coolant based on your engine’s maintenance schedule helps keep temperatures stable, protects vital components and extends the life of your diesel engine.

Neglecting filter maintenance
Diesel engines rely heavily on clean air and fuel, making filter maintenance critical. Dirty air filters reduce airflow, leading to poor combustion, increased fuel consumption and power loss. Clogged fuel filters can restrict fuel flow, starving the engine, damaging injectors and causing hard starts or stalling.

Over time, neglecting filter maintenance doesn't just impact performance; it can lead to long-term engine damage. Insufficient air or fuel flow can result in incomplete combustion, which produces more soot and unburnt fuel. This buildup can clog exhaust gas recirculation (EGR) valves and coolers, reducing their efficiency and contributing to higher emissions, rough idling and even EGR system failure.

In severe cases, dirty filters can lead to increased crankcase pressure and contamination of engine oil, accelerating internal wear.

Ignoring warning lights
Dashboard warning lights are there for a reason. Ignoring signs like the check engine light or glow plug warning can turn minor issues into major repairs. Address problems as soon as they appear to prevent further damage and avoid expensive breakdowns.

Failing to keep the engine clean
Dirt, grime and oil buildup can hide small leaks and lead to overheating or contamination. A clean engine compartment helps you spot issues early and ensures proper airflow for cooling. Regular cleaning also extends the life of hoses, belts and seals.

Well on coolant, a heavy engine antifreeze with the additive that stops pitting of the cylinder liners or the cast cylinder block.....forget the name of it.

Not getting it out at least every once in a while and working it hard for an hour or so, then changing the engine oil and filter.

Cranking it up every month or so to keep the oil particles in suspension, not deposited on the bottom of the oil pan as sludge.......to name a few.

 

[Hay Dude]

Well on coolant, a heavy engine antifreeze with the additive that stops pitting of the cylinder liners or the cast cylinder block.....forget the name of it.

Anti-Cavitation additive

Not getting it out at least every once in a while and working it hard for an hour or so, then changing the engine oil and filter.

Cranking it up every month or so to keep the oil particles in suspension, not deposited on the bottom of the oil pan as sludge.......to name a few.

Agree. Not good to let them sit too long.

 

[RayIN]

We, as a company had Auxiliary Power Units (APU's) installed at Kenworth prior to taking delivery ...

If the drivers will use them there is a huge savings in fuel, they roughly burn 1-2 gallons of diesel per "night" whereas my 15 liter Cummins burns .8-1.2 gallons of fuel per HOUR at idle ... Over the course of 4 years they more than make up the initial $13K cost ...

PLUS, they share the same coolant as the truck engine, so when I start the 15 liter the coolant is already 75°-125°F, so starts easier in the winter, and less warm up needed, besides it keeps the batteries topped up ... Yet many drivers insist on idling there trucks all night, even like last night in South Carolina it was about 70° when I went to bed, 52° when I got up ... I was snug in my sleeper, without even needing the heater in the APU! Or they leave it idling while fueling, then wander inside for another 15 minutes ...

You would be greatly surprised at how many ignorant diesel pusher motor-home owners will start the drive engine and allow it to "warm-up" every travel morning. This is contrary to what Cummins states in their engine owners manual. It states 3-5 minutes to get the oil circulating, then drive lightly until the engine reaches normal operating temperature.
As to motor oil changes, I let Blackstone labs say when to change motor oil in any engine that requires 5G or more.

 

[EzraWalker]

I was taught that only applies to diesels with glow plugs or pre-heat systems doesn't it??
used sparingly has been a staple for century hasn't it?
its still sold today for use on diesels by many manufacturers like Lucas etc..... approved for use on diesels.

happy to be proven wrong though.
Cheers

On the first diesel tractor I was taught to use as a teen, the old farmer carefully taught me to build a small fire and place a 5 gallon square kerosene tin with top and bottom cut out around it to shield it from breezes (since we were in the barn with the hay storage). Then we’d go in and eat a hearty breakfast while that tractor’s fuel and oil became something less than a sticky brick in the -70F temperatures. Once done we’d go out and he showed me the trick of starting it and the route to take for each task to avoid as much of the deadly winds blowing across that early morning farm as possible. Those were NOT the good old days!

 

[Sawyer Rob]

There are no farms where it is an honest, -70F...

SR

 

[DarkBlack]

There are no farms where it is an honest, -70F...

SR

Probably seemed like…-70

 

[GrandpaSmurf825]

I've been educated. Maybe Biodiesel has two major issues and I saw neither mentioned. 1. Even B10 begins to gel at around 30 degrees Fahrenheit and the higher the blend the worse it gets. 2. It cuts the power. Fact! B30 can cost you as much as 50%. I learned this in John Deere engine school. We used their power units. It was a (don't tell anyone because everyone wants to use bio diesel) secret you weren't supposed to tell.
Whomever said you can't overspeed an engine with a governor electronic or otherwise. Want to bet on that? You absolutely can. Hydrostatic machines with improper valving can do it. Trucks with manual transmissions and idiots behind the wheel can also do it. Did you know that they won't warranty an engine that's been over sped in a vehicle that way. The ECM logs every instance right up to the one that grenaded it. Who knew?

I've been around a lot of engines from little pony starting engines to 11,000 cubic engines with glowing exhaust manifolds. I treat turbo engines the same. They only need a minute or so to "relax" from a hard pull. The exhaust cools fast and the coolant temp drops quickly when the load is removed. Of course some don't get shut off at all but others do and when every looks satisfactory I shut them down.

If it's monitored for condition and coolant additive or spin on filters are used coolant will last forever. The PH balance is the critical element in keeping coolant where it needs to be. We literally had a couple thousand pieces of machinery and it was far cheaper to maintain the coolant than to replace it every couple years. We had spin on filters and PM mechanics that checked the coolant as part of the inspection. As someone mentioned. Heavy duty coolant is an important factor. Coolant isn't all the same and if you go buy cheap automotive coolant and mix it in the long term results will not be great.

Some things on the list I don't agree with.

Individuals aren't as likely to do it but businesses have a baseline oil sample taken and then monitor engine oil for abnormalities as the hours build up. It can give a heads up to bearing wear or coolant starting to get into the oil. Certain metals can only come from specific components on some engines so they can give early warning to an impending issue.

 

[Texasmark]

That list is pretty obvious, but here’s 2 others not on the list:

Lugging: lugging a diesel engine can be harmful as it may lead to increased wear and potential damage to engine components. It's generally better to operate at higher RPMs to ensure the engine runs efficiently and avoids stress.

I see this frequently. I see a lot of operators run at a lower RPM than they should.


Here’s another big one not mentioned:

Shutting off a hot turbocharged diesel: Shutting down a diesel engine with a turbocharger over 1200 degrees instantly stops the oil flowing through the turbo bearings. The oil can actually start “coking” in the bearings.

If you were to rev up your engine and then shut it off, it will cause damage and wear to the turbocharger as the oil pressure drops with it is still spinning at very high RPMs. Modern turbochargers can have turbine speeds above 100,000 rpm! Even the older models will have RPMs ranging from 40,000 to 60,000.

At these speeds, lubrication of the turbocharger bearings is super important for your turbo to last. The turbo must be allowed to spin down before the oil vacates. If not, you will be putting another turbo on before long.

Rod bearings around the crankshaft and main bearings, especially on older engines. that skimped on the number for a given length of engine. With the higher compression of diesel engines they get stressed more than equivalent hp gassers and used to be gassers would need upper overhauls where diesels would need lower overhauls.

 

[joea99]

I couldn't care less how long the fuel has been sitting.

Most of mine is about three years old by now, and one tank closer to 10. Treated and stored correctly it doesn't seem to matter one bit how old the fuel is.

You do you. How many low volume fuel places can you believe have correctly "treated and stored" fuel? Free of water/algae, etc?

 

[Too many Kubotas]

You do you. How many low volume fuel places can you believe have correctly "treated and stored" fuel? Free of water/algae, etc?

I don't worry about that. I can treat it myself for the conditions.

Any water is taken care of by filters and additives, but if somehow there would be algae in the fuel it'd be a new one for me.

Although, I have had quite a battle with bacteria in a fuel tank of a vehicle I bought.

Algae needs light to grow so it's not an issue in fuel tanks, and there are additives available deal with bacteria in fuel. Which needs water in the fuel to start growing, so not hard to avoid.

 

[Larry Caldwell]

I run my truck to the fuel light every tank for the most part. I figure if you always suck all the fuel out then there won't be time for lots of sediment to build up.

I will also say that when I ran a big excavator too low I was changing muddy fuel filters at a very inopportune time....

Tractors have a device to deal with dirt in the fuel. It's called a sediment bowl. The reason you don't let a diesel run low on fuel is that priming the injector pump is a PITA.

 

[Larry Caldwell]

"In diesel engines, where internal pressures and operating temperatures are often higher than in gas engines.."

That statement is wrong. Diesel burns much colder than gas and is less violent than gas, that's why diesel engines last much longer as diesel does much less wear and tear on the engine parts compared to gas

Yes, it's the compression ignition that is hard on the engine. Diesel hits hard. As you say, it runs cooler, but is similar to a compression knock in a gasser.