This issue has been reported happening on Epoch mod as well as Wasteland and KoH. A relevant excerpt from the Epoch forums post from user Havoc302: "Vehicles exploding when people get in them. I can only assume this is related to the file that loads the vehicles on the server, where near the bottom enableVehicleSimulation is set to false. So the vehicle is loaded in by the server (and is visually) floating, often you can see it drop a little when you approach it showing that simulation has been enabled but sometimes it doesn't do it. So you get into a vehicle that's obviously been damaged at the loading of the server but simulation doesn't happen until you get in, then it explodes. Enabling vehicle simulation at server load coupled with the above rotating damage handling fix should see these issues completely resolved."
Source: http://epochmod.com/forum/index.php?/topic/31193-vehicles-exploding-at-server-start-and-when-hopping-in-them/