Diesel engines are built to take a beating, but they’re not invincible. Unlike their gasoline-powered counterparts, diesels operate at much higher compression ratios. That means more heat is generated right from the get-go. Plus, many diesel owners tow heavy loads or run long hauls, turning up the heat. Overheating in a diesel can lead to warped heads, cracked blocks and many expensive repairs.
Explore why your engine is overheating, ways to diagnose the problem and how to prevent it from happening in the future.
Top 7 Causes of Diesel Engine Overheating
Here are some of the most common reasons a diesel engine runs hot:
- Low coolant levels: Coolant protects your engine’s cooling system, and if you’re running low, your engine will quickly overheat. Check your coolant reservoir regularly and top it off as needed.
- Cooling system leaks: Leaks can occur in hoses, radiators, water pumps or the head gasket. If you notice a sweet smell under the hood or see puddles of coolant, get it checked out immediately.
- Faulty thermostat: The thermostat regulates the flow of coolant to the engine. If it’s stuck closed, your engine will overheat.
- Clogged radiator: Debris, scale or corrosion can clog the radiator, reducing its ability to dissipate heat. Keep your radiator clean and clear of obstructions.
- Broken water pump: The water pump circulates coolant throughout the engine, and if it fails, your engine will overheat fast. Listen for unusual noises from the water pump area, and replace it if you suspect it’s going bad.
- Oil-related issues: Your engine oil helps to transfer heat away from critical components. If your oil is low, old or the wrong viscosity, it won’t be able to do its job, leading to overheating.
- Heavy towing: Towing heavy loads or running at high RPMs puts extra stress on the engine. The cooling system may be unable to keep up.
Regular diesel engine maintenance is the best way to catch issues early and keep your diesel engine in shape.
Why Is My Diesel Engine Overheating While Driving?
Have you noticed your diesel creeping into the red zone when cruising down the highway or pulling a heavy load? High speeds and air dams or other aerodynamic components can deflect air from the radiator, leading to overheating. While your turbocharger works hard to boost engine power, it generates heat that can overwhelm the cooling system. Some vehicles have transmission coolers integrated into the radiator. If the transmission works hard, it can dump excess heat into the cooling system, contributing to overheating.
| Stressor | City Driving | Highway Driving |
| Airflow | Stop-and-go, reduced airflow | High speed but potential airflow disruption |
| Engine Load | Idling, light acceleration | Sustained high RPM, heavy load |
| Turbo Strain | Minimal | Significant |
| Transmission Heat | Less heat generation | More heat generation |
| Typical Temperature Impact | Gradual increase, may stabilize | Rapid increase, harder to control |
How to Diagnose an Overheating Diesel Engine
When your engine’s running hot, follow this step-by-step checklist to determine why:
- Check the coolant reservoir and radiator to make sure the coolant levels are where they should be.
- Inspect that the fan is spinning freely and the belt is in good condition.
- Use an onboard diagnostics (OBD2) scanner to check for any trouble codes related to engine temperature or the exhaust gas recirculation (EGR) system.
- Check oil levels and change dirty oil.
- Look for leaks or bubbles in the coolant, which could indicate head gasket issues.
If you can’t perform these checks yourself or if the problem persists, consult a qualified diesel mechanic.
How Hot Shot’s Secret Products Can Help Prevent Overheating
Hot Shot’s Secret can help if you want to protect your engine from overheating. Our products are specially designed to keep your diesel running cool and efficient.
Hot Shot’s Secret Diesel Extreme
This fuel additive cleans your fuel system, improves combustion efficiency and reduces internal stress and heat. It also prevents injector coking, which can lead to incomplete combustion and increased heat. Use Diesel Extreme every 6,000 miles to keep your engine clean and cool.
Hot Shot’s Secret Stiction Eliminator
Our oil treatment reduces internal friction and cleans oil passageways, helping oil transfer heat more effectively. This formula is especially helpful for older diesels or those with frequent stop/start duty cycles.
Hot Shot’s Secret Blue Diamond Oil
This full synthetic oil offers superior thermal stability for high-temp performance. It reduces breakdown during towing, hauling or extreme driving, providing excellent, lasting protection.
Hot Shot’s Secret Antifreeze
Our antifreeze is available in three heavy-duty formulas to keep your engine from overheating. Choose Red for 750,000-mile ultra-long life, or select Yellow or Green for 150,000-mile extended life. Antifreeze protects against corrosion and deposits, keeping your cooling system at peak performance.
What to Do If Your Diesel Is Overheating
If you notice your diesel engine overheating, take the following steps:
- Find a safe place to pull over and shut off the engine.
- Allow the engine to cool down completely before attempting to add coolant.
- Wait at least 30 minutes before checking for any signs of coolant leaks.
- Call a tow if necessary — continuing to drive could warp the head or damage the pistons.
Emergency kit tip: Keep coolant, water and a Hot Shot’s Secret Diesel Extreme bottle in your truck at all times
Diesel Engine Overheating FAQs
Learn more about preventing overheating with these FAQs.
Will Low Oil Cause My Diesel Engine to Overheat?
Low oil levels mean less fluid absorbs and carries heat away from critical components like pistons, bearings and cylinder walls. Beyond reducing friction and controlling temperatures, oil also helps to lubricate these parts. Without enough of it, friction soars, generating even more heat. Maintain the correct oil level and use a high-quality formula like Hot Shot’s Secret Blue Diamond to ensure optimal cooling and lubrication.
How Often Should I Change My Coolant?
Refer to your vehicle’s owner’s manual for the manufacturer’s recommended cooling system flush interval. Generally, it’s recommended every 24,000 to 36,000 miles or every two to three years.
Can Additives Really Reduce Engine Temperatures?
Absolutely! Certain additives, like Hot Shot’s Secret Diesel Extreme and Stiction Eliminator, improve engine efficiency and reduce heat. Diesel Extreme cleans the fuel system and promotes more complete combustion, which means less wasted energy in the form of heat. Stiction Eliminator reduces internal friction, allowing the oil to flow more freely and carry heat away from critical components.
Don’t Let Heat Wreck Your Diesel Engine
Overheating poses a serious threat to diesel engine health and longevity. By understanding the causes, consequences and prevention methods outlined above, you can protect your engine from costly damage and ensure reliable performance. Protect your engine from the inside out — explore our full line of performance additives and oils.