OH is currently dealing with the exact same problem! He only became aware of mice in the bonnet after the garage told him when the car went in for an mot. Like @Topbird he has set mouse traps baited with peanut butter and has killed 5 so far.
Shortly after we moved here - former farmhouse left vacant for 3 months and rodents from field mice to rats resident in the grounds and outhouses - we found that the insulation under one of the car's bonnets had been significantly chewed.  Had the car checked over to make sure all the wiring was OK and put down poison in strategic places.
Haven't had the problem since but we do have 2 cats and 2 dogs and the cars don't sit for more than a few days as there are no shops within walking distance.
When I worked in a garage a customer bought his van in for some work when the mechanic opened the bonnet he found a kitten inside the engine bay it had travelled five miles from the the company depot and didn't show any sign of distress, it hadn't been eating the wiring just getting warm maybe.
I bought some peppermint oil today & sprayed the engine compartment & round the tyres with it, the shop assistant said she’s had other people buy it for rodents. We have traps & sonic devices coming in the post so thanks for all the info.
I’m a bit reluctant to put down poison as next doors cat actually sits under the car a lot but that’s more to pounce on birds from what I’ve seen in the past! Maybe it’s just not a mouser? The car gets used daily so I don’t know why they’ve just started doing this & next door have 3 cats which come in our driveway & garden!Â
It might just have been a one night / single curious mouse event Astrantia - let's hope so.We preferred the snap traps because they're usually a quick, clean kill and you get to see the results. Any of those in exposed outdoor locations (eg near car wheels) should be in proper boxes so that birds etc can't be harmed.
Similarly any poison blocks or trays should always be in a locked bait box so other wildlife and children can't get to it. I did use poison for dealing with rats when we had a problem around the compost bins a few years ago - but that was mainly because there's no way I could handle a dead rat to get it out of a spring trap.
Don't like using poison - it's a slow, painful death and there's a risk of poison entering the food chain for predators such as owls and cats.Â
Heaven is ... sitting in the garden with a G&T and a cat while watching the sun go down
My husband owns a garage; car repairs, MOTs etc and he very regularly sees mouse damage in car engines.  Sometimes just a nest but sometimes very extreme damage with the wiring and electrics.  He’s had cars that have had to be written off as the damage was too costly to repair.  He says he finds it’s mainly Japanese makes … Hondas or Toyotas but that may be because a lot of our customers drive them. Â
Our cars are parked overnight in our carport so we always have humane mice traps in there, baited with chocolate so they visit them before our car engines!  We go through phases of finding a mouse in the traps in the morning which we then release.  I wonder and say to my husband that we might be enticing them into the carport with the chocolate, but he is so paranoid about a mouse getting into the engines having seen what damage they can do, that it’s an argument I’m not going to win!!!
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Haven't had the problem since but we do have 2 cats and 2 dogs and the cars don't sit for more than a few days as there are no shops within walking distance.
The car gets used daily so I don’t know why they’ve just started doing this & next door have 3 cats which come in our driveway & garden!Â
Similarly any poison blocks or trays should always be in a locked bait box so other wildlife and children can't get to it. I did use poison for dealing with rats when we had a problem around the compost bins a few years ago - but that was mainly because there's no way I could handle a dead rat to get it out of a spring trap.
Don't like using poison - it's a slow, painful death and there's a risk of poison entering the food chain for predators such as owls and cats.Â