Entire male dogs and fighting

[Confusedandmystified]

We have two male springer spaniels. Both are entire males. They are 7 and 4years of age.
For the past 2 years they have been fighting. This has always been limited to the back of DH pick up truck. After trying to stop the fighting they are now in separate crates but still sound like they are going to kill each other for the first 5 mins of any journey. Highly embarrassing and I feel like I have to explain that it only happens in the car to passers by, as we also have 2 very young children.
Recently the younger dog has started waiting for the older one and pouncing ready to fight when they exit the car. Leads, distractions etc do not work.
It has been increasingly getting worse and younger dog went for older dog when going into the back garden today.
I am booking younger dog in on Monday for the snip.
My question is, will just having him neutered help at all? He is the problem. He always starts the fight and the older dog has to defend.
Does anyone have any experience of this/advice?
Younger dog is more aggressive/defiant in the home but a really chicken when we go out. Older dog is a placid gentle giant.

Castration may have prevented this issue however it has become habit now so whilst castration is likely to improve things it may not resolve the problem.

Why are they still entire?

My terrier totally calmed down after being castrated. He was often picking fights with other dogs. He's never done it since castration. He's also fatter

I have two dogs - one castrated the other not. The non castrated dog is aggressive to other dogs whilst the castrated dog often starts ww3 with his older brother. I believe that if they were both castrated there would be fewer issues.

It probably would have helped a long time ago, now unlikely but I would start with getting both castrated regardless.

Then get in a qualified behaviourist to assess them and tell you what’s going on. It will be the best money you ever spend as they usually write a plan to follow so you can’t get it wrong and make the problem worse.

Is anyone ever injured or is it all noise?

My dog was neutered at 5 and it has calmed him down a bit, but sad to say he’s still a fighter.