Plot hole: Even if boys of that age had the technical know-how to quickly repair Jeeps over 20 years old (seriously?), any gasoline in the tank would have long become unusable, the tires and lines would have rotted away, and the electrics would all be dead. Now if it was in the desert or a dry garage, it may have survived, but it's on a tropical island, in a shed that has all sorts of holes in the roof, leaving it exposed to every kind of weather the island could throw at it. In addition, the kids start the jeep with the small battery of an ATV, which cannot produce enough power to crank a Jeep engine.
Suggested correction: It is not uncommon for youngsters to want to help family members when fixing cars, it also wouldn't take much to know how to change a battery and put some fuel in. The gasoline came from the crashed ATV outside so it is therefore fresh. In regards to the age of the vehicle, it is not known when it was last used. It could have been used by builders whilst Jurassic World was under construction. Judging by the difference in condition between the garage and the main rotunda, it looks like the garage has been somewhat maintained which would back this theory up. It is also worth noting that the Jeep was left to rot after filming and that is genuinely the condition they found it in, apart from putting new tires on it they didn't have to do any mechanical work to get it running so it is indeed possible to get a vehicle running that has sat for years. In regards to the battery, there have been huge advances in technology. I have a classic Capri which used to use a huge lorry / forklift battery. It will now start off a battery from a 2008 Ford Focus.
No it isn't possible to get a machine that's been sat for years without first repairing it, especially since machines that have been sat for years become non functional due to the damage by the effects of aging.
I'm a mechanic and can confirm that a car will start after many years without "repairing it." Yes it won't start as easily as the Jeep did in the film, but it will definitely start without needing to replace anything other than fuel and the battery. There's also plenty of videos on YouTube of people starting cars that have sat for years and years.
Anyone who thinks the jeep wouldn't start should head over to youtube and watch some barn find videos. That jeep was immaculate compared to some of the things you see start up for the first time in decades on youtube.
There's a road leading right to the garage, one Claire knows about because she says it leads to the new park, it IS overgrown but no tropical trees have sprung up in 2 decades, it all kinda suggests those jeeps might have been used far more recently. The truth is, we don't know. It could have been 20 years, 2 years, or some park employee had a pet project and it was 2 months since they last ran. Someone had been in there to replace the night vision goggles' batteries.
Plot hole: What broke the gate the boys went through while driving around in the gyro-sphere? As far as map tracking of the I-Rex it couldn't have been her. So what dangerous dinosaur was hanging out in the west plains?
Suggested correction: It was the Indominous Rex. A major plot element is the fact the Indominous Rex can camouflage itself and hide its heat signature making it impossible for humans to track. The heroes then attempt to track the creature using the velociraptors.