If none of the above-mentioned ways of preventing the rodents from your car engine compartment seems to be successful, you can try this natural method also to check whether it works. Yes, you can surely use peppermint oil in a car engine to keep the naughty tiny creatures out of your car engine. The scent of peppermint oil acts as a natural rodent repeller as the rats generally do not like the smell of peppermint oil. You can use cotton balls and soak them in the oil and then throw them in the car engine or the car interior to make it more effective, as the effect will last longer than usual when you use cotton balls.