Please assist I need to create a unit that dispenses an agent into my trucks fuel tank on filling up. It must measure the fuel and then every x amount of fuel it puts in x amount of agent.
I have no knowledge on electronics so please assist. 
Hi, it would be doable with arduino, the hardware would be the problem.
I assume the fluids are flammable so special requirements for flow measurement and dispensing valve.
Tom.....
Do you have access to the signals in the fuel pump meter? To avoid the issues involved with attempting to get into the existing plumbing, I'd go about it thus.
Your additive dispenser sits on the pump. As the fuel is dispensed, the quantity gets noted on the arduino. As the fuel pump gun is placed back into it's holster, the arduino will beep. User then picks up additive hose places into tank and presses button. The correct amount is automatically dispensed and resets the arduino ready for the next truck.