As soon as the move was made, a text message was sent from one friend and colleague to another.

“Sarcastically, I asked him if he was a masochist,’’ Charlie Weis said of his text to Romeo Crennel.

Crennel had just been named interim head coach of the 0-4 Texans, who this past week fired Bill O’Brien after six-plus seasons in Houston.

So on Sunday, when the Texans play host to the Jaguars, Crennel will become the oldest coach in NFL history at 73 years and 115 days old, according to Elias Sports Bureau (only George Halas and Marv Levy have coached a game at more than 70 years old).

“I’m just a football coach, and I enjoy coaching,’’ Crennel told reporters this week. “That’s why I’m still coaching.’’

Crennel, who has coached in the NFL since 1981 with six different teams and been a head coach twice, with the Browns and the Chiefs, is one of the good guys in the game, easygoing and respected.

“Romeo is like your grandfather: You just don’t want to disappoint him,’’ Weis, a former NFL and college coach who’s now a SiriusXM radio host, told The Post. “Even though he’s laid back by nature, he’s definitely got plenty of fire in him. He’ll be a more reserved-mannerism guy than [O’Brien] was.

Romeo Crenell
Romeo CrenellAP

“I think that right now, that soothing grandfather type that Romeo is where players, when things don’t go well, feel like they disappointed him, will be a welcome change right now.’’

Weis, who coached alongside Crennel with the Giants and Patriots and remains close friends with him, said it was Crennel’s presence in Houston that allowed Texans owners to make the in-season coaching change.

“Everyone wants to fire the coach,’’ Weis said. “But who are you going to give the job to, to finish out the rest of the year? If you don’t have somebody to give it to in the building that makes sense, you’re better off not doing it. [Crennel] definitely makes sense. He’s a guy that’s going to change the personality, change the tension in the building.’’

A sign of how much Crennel is respected: As he was being fired, O’Brien recommended to Texans ownership that they name Crennel as his successor.

“I hope our attitude and energy is different, and then I hope that our performance is different,” Crennel said. “You’re not going to come in and put in a new offense or new defense just overnight, because it takes time.’’

Barring a miracle, this will be a 12-game gig for Crennel before the Texans find a younger head coach to take over next season, because NFL teams aren’t usually seeking to rebuild with a 73-year-old leader.

“We right now have a fresh start,” said Texans star defensive end J.J. Watt, who reportedly clashed with O’Brien in a recent rant at practice. “ ‘RAC’ is a great man. He’s seen a lot. He’s been round a lot. He has [Super Bowl] rings, and he has a positive air about him. He has just kind of a jolly nature to him.

“So, you can’t really help but smile when you’re having a conversation with RAC. I’m looking forward to seeing what he can do and what he brings to our team. It should be fun.”