I kept having rat problems in my rarely used truck and its engine, I tried to put a light in there, I tried moth balls, I put traps in there, I finally solved the problem by parking my truck on metal ramp stands, I think the rats don't like the angle and also that the truck is higher off the ground. This has been working for about a year now. (I am just charging my battery, I don't have to leave the hood up to keep the rats out)
