Dealing with Rodent in Engine Compartment

Recently discovered that mice (or possibly small rats) have been taking refuge from the weather in the engine compartments of our two vehicles, which are typically parked in the open driveway.

Discovered this about eight weeks ago. Rodents had set up nest in at least one of the vehicle engines, evidenced by the piles of yard debris and food wrappers on top the battery and throughout the compartment. Both vehicles showed evidence of being frequented, having accumulated “waste” matter, urine stains and footprints. Wires and belts seem to be okay. Noticed only single area of plastic housing (about the size of a dime) that appeared to have been gnawed and another area where possibly some insulation had been pulled away. No evidence of rodents in trunks or vehicle interiors.

I cleaned out the engine compartments using a leaf blower and wiped down the urine-stained areas with vinegar/water mix. Done this a few times. Cleaned out surrounding areas along the driveway and nooks around the house that had accumulated leaf litter where it seems rodents were hanging out too. Tried temporarily parking the vehicles out along the street and at different locations along the driveway to make access inconvenient. One vehicle is favored over the other. The favored vehicle is lower to the ground (easier access) and sometimes sits inactive for several days at a time without being driven. The food wrapper problem stemmed from construction crews leaving a mess at neighbor’s property, but that seems to be under control now.

Was looking online for solutions and found suggestion to apply peppermint oil. I did this a few days ago. Wiping peppermint oil over areas they sit and leaving a few oil-soaked cotton balls throughout compartment. It smelled nice walking past the cars, but it did not deter the rodents from returning. As if to taunt me, a rat “pellet” was even left on top of one of the cotton balls.

I guess next step is to place traps on the ground underneath the vehicles. Was hoping to avoid this. Any other suggestions or success stories to offer?


P.S. I’m certain this topic has been addressed on this board before. But search did not pull up any previous threads.
P.S.S. Ha ha. Community rules don’t allow me to call out rat waste for what it really is. Words prohibited.

In the past I have read using moth balls is a good deterrent. Sure won’t smell as good as the peppermint oil though! Unfortunately, a quick Google tells me that’s useless too. Of course it’s an exterminating company that posted the rebuttal, so who knows. Perhaps try googling it and let us know what worked for you.

Good luck!


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My daughter’s Honda was visited by rats. The insulation Honda uses is particularly tasty, apparently. I’ll take the rats’ word on that one.

After the wiring harness was repaired we put a cup of moth balls up under the hood. We literally took a plastic cup, punched two holes in it, and wired it up under the hood near the firewall. Filled it with moth balls. The rats did not return. Did the moth balls work? I don’t know for sure, but I’d try it again.



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Talking to my mechanic, years ago, he was in the process of replacing the hole loom of an early Volvo dan, the insulation was falling off the wires, looked like crumbly cheese, maybe as tasty, later models that corrected the insulation, but it was a nasty mess, lucky it didn’t catch fire… And I’ve not considered buying a Volvo after that…

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Mothballs do work, Also “Bounce” or similar laundry products. Also, air fresheners. In short, anything that gives off a smell the critters don’t like.

Thank you all for your replies and suggestions. When I initially searched for solutions, I read about the mothballs, bounce and air freshener ideas. Seemed like mixed results and nothing a sure thing. The peppermint oil sounded a bit more promising. I may try the mothballs next. I do have mothball crystals and will try wrapping some in a coffee filter and taping the package within the engine compartment. Also, I am making a point to drive the vehicles every day to make it less appealing for the rodents to nest. Also, I read that keeping the area lit/bright can help, so I have switched on a flood light in the problem area of the driveway.

Agreed that the mesh cloth wrapped around some of the wire bundles seems to be the (preferred) insulation that the critters have gone after, at least in one of the vehicles.

Hoping the combination of lights, peppermint oil, moth crystals and daily movement of the vehicles will get us over the hump and send the message for the rodents to move on. Going to give it a few weeks and will report back.

Please feel free to share any additional suggestions.

  • MT
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Another misunderstanding is the use of mothballs
in outdoor areas to repel rodents, squirrels, bats,
snakes or other wildlife. Mothballs are ineffective for
this use and can contaminate soil and water. Using
mothballs as animal repellants is not appropriate and
can be illegal.

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No. That is not true. Mothballs can be very effective. My neighbor used them with good success to discourage racoons from pooping in his garden.

Whether there are better, more environmentally-friendly means is a whole 'nother matter.