NASCAR engineer shares possible causes behind Denny Hamlin’s Next Gen fire at Texas

At the NASCAR Cup Series race that happened at the Texas Motor Speedway this past weekend, Denny Hamlin's #11 car faced an early exit from the event after it caught on fire on lap 75. NASCAR engineer and technical director Joey Cohen appeared in an interview recently and explained how the Next Gen vehicles have their exhausts built in such a way that allows for a lot of heat to get trapped, with oxygen flowing towards it that can start a fire.

In conversation with mechanic Bozi Tatarevic, Cohen explained how cars like Joe Gibbs Racing's #11 are built, starting from previous iterations of the vehicle, which had their exhausts coming out towards the front of the rear tires, proving to be a problem.

"The exhaust used to run the full length of the rocker panel, so we used to exit the exhaust in front of the rear tires. What we come to find out there was those exhaust pipes under the driver were carrying a large amount of heat and just soaking that underside of the chassis, basically cooking the drivers," he explained [23:20].

About what happened with Denny Hamlin, Cohen explained how the current version of the NextGen car can get overheated, especially in a hot place like Fort Worth, Texas.

"Essentially, now the exhaust diffuses right there behind the front tires. It's a very short exhaust from the headers and the collectors, there off the engine,e so there is a lot of centralized heat still there. You've still got a lot of components that are running near composite panels, some things that are very flammable when they do get hot enough or they get some sort of igniter put on them," he said [23:56].

"In this case, probably looking at some engine fluids. It's not out of the ordinary for that space underneath the car there to be well over 300-350 degrees especially [on a] moderately warm day at Texas," Cohen added.

Cohen went on to explain how the Next Gen car is also built to be as low on the ground as possible, which helps it go faster, but it restricts the movement of air to the parts that can get hot. During the car's building process, NASCAR chose to build air ducts to cool those areas, but the oxygen being fed to them can also fuel a fire, like what happened with Denny Hamlin.

“To kind of cool things NASCAR has to electively create these ducts that will channel and force air to those areas of the car to kind of keep air moving across them, and fire and oxygen, it'll feed a fire pretty quick,” Cohen continued [24:51].

Denny Hamlin's DNF at the Würth 400 presented by Liqui Moly saw him score a result of 38th place, his lowest of the 2025 season.

"It’s tough to say exactly what it is": Denny Hamlin shares his thoughts post-Texas misfortune

Denny Hamlin (11) is introduced before the start of the Wurth 400 race at Texas Motor Speedway, May 4th, 2025 - Source: Imagn

Denny Hamlin's #11 car catching on fire on Lap 75 was not the first indication the driver had that something had gone wrong. After the race, the JGR driver shared that he got the sense of trouble a lap before the car exploded, and quickly reacted to make sure that the car was in shape for the engineers to figure out the true cause of what went down.

“It was blowing up for about a lap or so before it really detonated,” Hamlin said [via NASCAR]. “I tried to keep it off to keep it from full detonating.

“That was so they can diagnose exactly what happened to it. It’s tough to say exactly what it is, but they’ll go back and look at it and we’ll find out in a few weeks,” he added.

Despite this setback, Denny Hamlin still sits third in the drivers' championship standings with 338 points, tied with fourth-placed Chase Elliott.