5.9 Cummins Difficult Hot Start

Several issues could be causing hot start difficulties in your 5.9L Cummins:

Leak in the Fuel System

If your truck exhibits long crank times or loss of prime, it might have a leak in the fuel system. Loose or damaged fuel lines can cause air to leak into the fuel system, leading to fuel delivery problems. The difficult hot start may also be due to leaking injector O-rings, which allow air to enter the injector system and reduce fuel pressure. Replacing damaged fuel lines and leaking O-rings should fix the issue. 

Poor Fuel Quality

If your truck struggles to start or stalls when the engine is hot, the problem could be caused by contaminants in the fuel or insufficient lubricity. It could also be caused by water or bacteria in the fuel system. Replacing the fuel filter, draining and replacing contaminated fuel, cleaning the tank and using a state-of-the-art fuel additive like Diesel Extreme will clean and protect your fuel system. 

Worn Fuel System Components

Insufficient fuel supply to the injection pump when the engine is hot, or a faulty fuel pressure regulator can contribute to hard hot starts. You might also notice inconsistent fuel pressure or loss of power. To enable the system to deliver adequate fuel pressure when the engine is hot, test the lift pump and fuel pressure regulator and replace them if necessary.  

Heat-Related Vapor Lock

When your engine cranks but doesn’t start after running at high temperatures, fuel may be vaporizing in the fuel lines due to heat soak — when parts of the engine stay hot even after turning it off. A vapor lock can also occur when air enters the system and displaces the liquid fuel. To fix the issue, inspect and replace improperly insulated fuel lines and those damaged by heat soak.

Using a top-quality fuel additive like our Everyday Diesel Treatment can also benefit your engine by improving lubricity and reducing the likelihood of vapor lock. 

Hard starts can cause unnecessary strain on your engine and increase wear on components, resulting in more frequent repairs and higher maintenance costs. By diagnosing and fixing hard starts, you ensure smoother engine operation, improve fuel efficiency and prolong the life span of your engine.

Here are three ways to diagnose and fix Cummins 5.9L engine hot start issues:

• Visual inspection: Examine the engine for leaks in fuel lines, injector O-rings or connections. Check for signs of contamination and dirty or clogged fuel filters. Tighten any loose components and replace damaged ones.
• Fuel pressure test: Conduct a fuel pressure test while attempting to hot start the truck to check for insufficient or erratic fuel pressure. Using a fuel pressure gauge, test the lift pump and regulator performance to identify and replace failing components. 
• Inspect for fuel quality issues: Check for signs of water, dirt or microbial contamination in the fuel. If you find any of these, drain and clean the fuel system, replace contaminated fuel and treat the system with advanced additives like Diesel Extreme.

Minimize the chances of hard hot starts in Cummins 5.9L engines with our third-party tested formulas. 

Hot Shot’s Secret Diesel Extreme

Diesel Extreme is a six-in-one engine additive that boosts performance and efficiency.

It cleans injectors and the entire fuel system, removing stubborn diesel injector deposits (IDIDs) that can cause starting issues. Diesel Extreme also boosts your engine’s cetane rating and reduces DPF regeneration cycles, helping improve overall reliability. Diesel Extreme also works to demulsify water and stabilize diesel. Add it to your fuel system as an initial treatment to address fuel quality problems that lead to difficult hot starts. 

Hot Shot’s Secret Everyday Diesel Treatment (EDT)

Hot Shot’s Secret Everyday Diesel Treatment (EDT) helps maintain fuel system health by preventing common diesel issues and improving fuel quaility.

The fully formulated product ensures consistent fuel system performance. Use it with every fill-up to increase fuel mileage and lubricity. Engineered to boost fuel economy, power and performance, EDT also maintains clean fuel injectors, maintaining efficiency and a proper spray pattern for optimal engine operation and long-term protection.