JOLIET, Ill. — Tyler Reddick said after the eero 400 Sunday (July 5) that he had no idea what punctured his radiator midway through Sunday’s NASCAR Cup Series race at Chicagoland Speedway. We have discovered the culprit.
Reddick came down pit road just before the end of Stage 2 with his car covered in oil and coolant. The sludgy mixture coated his pit stall and three others next to him. As soon as his crew saw it, panic set in, and the No. 45 team frantically began searching for the cause of the issue.
Then, a crew member emerged with a small metal rod, less than a half-inch in thickness, that he plucked from the grill of Reddick’s Toyota.
Reddick went behind the wall, where the team was allowed to change the radiator and oil cooler – a process that may seem simple on the outset, but requires a bit more legwork than swapping one out in my old beater pickup. As racecar mechanic Bozi Tatarevic explained, a full duct assembly has to be removed in order to access both the radiator and oil cooler.
The process took 28 laps to complete from start to finish, with no small amount of that time being spent wiping the sheer amount of sludge from the car so that it was safe to return to the track.
In reality, the piece that punctured Reddick’s radiator was a simple piece of equipment used to hold the Next Gen car’s rear diffuser in place, according to Tatarevic. Given the amount of air pressure it’s meant to support, the small rod has to be stiff enough to hold the diffuser together and support it at high speed. It makes sense, then, that the diffuser stay would be strong enough to puncture both Reddick’s radiator and oil cooler if it hit at high speed, which is exactly what took place.
Reddick was allowed to replace both parts, as they were deemed to be a mechanical issue caused by running over debris on the track. If it had been another car that caused the puncture, the replacement wouldn’t have been allowed.
A few cars spun on the track before Reddick’s mishap, but the most likely candidates as to who the rogue diffuser stay belonged to were the No. 33 of Austin Hill, who backed into the outside wall after being turned by Shane van Gisbergen, or Carson Hocevar, who was turned into the outside wall by Zane Smith in the race’s early stages.
Such a small part had a big impact on the race’s outcome. While Toyota did manage to place seven cars inside the top 10, Reddick and the rest of the 23XI crew were consistently a part of the mix all night long. The five-time winner in 2026 began the night second in points, and while he still holds that spot, Ryan Blaney closed the gap with a seventh-place finish.
Blaney now sits 69 points behind Reddick in third ahead of the Cup Series’ next stop at a drafting track, EchoPark Speedway in Hampton, Geo. With only ovals remaining on the 2026 schedule, the upper echelon of the points standings could get interesting as the Chase cutline nears.
Tanner Marlar is a staff writer for Sports Illustrated’s OnSI Network, a contributor for multiple automotive news outlets, an award-winning sports columnist and talk show host, and a PhD. student at a premier college of media and mass communication. Tanner began working with Frontstretch in 2022, covering the O'Reilly Auto Parts Series.
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