How to spot a failing EGR cooler

Updated Oct 16, 2023
An EGR valve.
An EGR valve from Detroit Diesel. The valve controls the EGR cooler.
Detroit Diesel

EGR coolers are meant to last the life of the truck, but depending on duty cycle and maintenance habits, customers may occasionally find themselves facing a failing part. When they come to you for help, here’s what you need to know.

Nitrogen oxide forms when the extreme heat generated by the engine combines nitrogen and oxygen. If the combustion chamber gets too hot, the chemical bond breaks down, releasing nitrogen oxide.

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EGR coolers are heat exchangers — EGR stands for exhaust gas recirculation. They take the hot exhaust gas, pass it over engine coolant, reducing nitrogen oxide emissions. According to the U.S. Environmental Protection Agency, NOx emissions accounted for about 6.2% of greenhouse gas emissions in the U.S. in 2021. Under pressure to reduce emissions, engine manufacturers looking for a way to reduce NOx landed on EGR coolers.

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“It’s relatively new to diesel engine technology,” says Len Copeland, product marketing manager for Detroit Diesel, which added EGR coolers to its engines in 2002.

The EGR cooler is located between the turbo and the EGR valve on the engine, AMBAC International says. The EGR valve connects the engine’s intake valve to the exhaust valve. The EGR system uses a hollow tube or series of tubes to recirculate the gas back into the engine. The coolant passes through a series of tubes next to the EGR valve, creating an inert, cool exhaust gas and lowering the temperature of the combustion chamber.

The EGR cooler was the simplest way to reduce NOx in the system, Copeland says, because the inert gas was already present in the engine.

“We don’t have to have a new tank of air or fluids on the vehicle,” Copeland says.

The EGR cooler is controlled by a vehicle computer through the EGR valve. The system dispenses coolant based on the temperature of the combustion chamber. Excess heat is transferred to the vehicle’s cooling system and dissipated using the radiator.

Jay Daran is the marketing manager at Roadwarrior, a company now makes an aftermarket EGR cooler under the Evercool brand.

“EGR coolers are difficult to manufacture because it’s a small thing of tubes and fins,” says Jay Daran, marketing manager at Roadwarrior, which has an aftermarket EGR cooler line. And those small parts make it difficult to manufacture and vulnerable to mishandling.

“That’s why there’s not many aftermarket options available,” Daran says.

EGR coolers require regular cleanings and, depending on the cleaning method used, those delicate parts could be damaged or weakened.

“It’s best to use a special EGR cooler cleaner to get rid of debris,” says Robert Isherwood, CEO of AMBAC International.  “EGR cooler detergents tend to be the best when it comes to removing carbon build-up, but some of these products may be slow-acting. You should never use flammable cleaning materials, as they may ignite inside the engine.”

AMBAC says some shops use ultrasonic technology to send vibrations through the cooler cleaning it in a matter of minutes.

Detroit Diesel’s latest EGR cooler includes design improvements that make it easier to replace and maintain, Copeland says, including a specific diagnostic code in DetroitConnect. The input and output coolant tubes are integrated into the block of the engine, reducing failure points and making the part smaller and lighter. The part has also been standardized across all Detroit engines.

“It makes it less prone to parts shortages,” Copeland says. “It’s easier to stock for parts counters as well.”

If an engine manufacturer doesn’t have a diagnostic code for its EGR cooler, other signs of a failing part are white exhaust steam or smoke coming from the tailpipe.

“This usually means the cooler is either cracked or leaking due to gasket failure,” Isherwood says. “If the coolant seeps out of the valve it will mix with the exhaust and start to boil as it moves through the engine, which causes the gas. It could also mean there’s condensation on the cooler, which can lead to steam.”

Daran says high exhaust temperatures are another sign the EGR cooler is having problems. That will trigger the check engine light or even put the truck into limp mode.

“High temperatures could start with a clogged DPF, which would also mean the EGR cooler has a clog and it would pretty much cook the EGR cooler,” Daran says.

Isherwood says a failing EGR cooler is one repair, but running on a damaged or broken cooler can lead to thousands of dollars in more work that would need to be done.

“If you have a leak and too much coolant enters the engine intake valve, it could lead to what’s known as hydro-locking, which damages the internal components of your engine,” he says. “Coolant doesn’t compress like air and fuel, which puts added pressure on the combustion chamber, including gaskets, rods and bolts.”

Note: This story has been updated. 

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