Fruit of the loom

I recently had expensive electrical problems with my car and the garage found that something had been chewing the wiring. The mechanic said they often see that nowadays, and it’s because the wiring is poor quality. Is this right, and how can I stop it happening again?

It’s certainly a problem, and not just out in the country - although rural garages do see more rodent damage. The insulation on wires used to be made from plastic products, derived from petroleum and not appetising to animals. However, car makers are under great pressure to reduce the environmental impact of their vehicles, including when they are ultimately disposed of. Everlasting plastic is a serious problem for recycling, so the insulation on modern vehicles is biodegradable. This means it’s made from a mixture of natural ingredients such as soya, rice, peanuts and so on. Great for recycling, but it turns out that it can be a tempting snack for any passing rodent, especially if they are taking advantage of the warm, snug engine bay as an overnight shelter. The damage can be extremely expensive to put right. Tracing all the broken connections, and getting to the components affected to replace the damaged loom can be very time consuming and racks up large labour charges.

There are various deterrents, but none that seem 100% guaranteed to work for every cable chewing critter. An ultrasonic box, powered by the car’s battery, will set you back about £15 - £20 and can be fitted very easily. The high pitched noise is too high for us to hear, but annoys rats and mice so they go elsewhere. Some have randomly flashing LED lights as well which apparently annoys them even more. If your car is left for long periods and a flat battery is a concern, there are some powered by their own AA batteries. If your car’s in a garage, leaving the bonnet up is a good idea since they like somewhere warm and dark to snuggle and snack.

Lots of sprays are available for around £7 - £15 which make the car smell unappealing with a cocktail of natural ingredients. Most products seem to have a heavy dose of peppermint and are poison free, so harmless to people and pets. An alternative recommended on many web sites is Irish Spring soap. It has a powerful deodorant-type smell and many victims of vermin swear by taping little blocks of it around the engine bay, but keep them well away from any heat sources.

Old fashioned mouse traps are an option, but they don’t have a deterrent effect; they simply catch some of the pests before they do any damage. It’s hard to say what works for certain, because you just have to wait and see if the symptoms of rodent attack stop.

One essential is to make sure you’re not tempting them into the vicinity of your car. Bread or seed thrown out for birds is a tasty starter for them. There’s no evidence either way that cat owners are less prone to attack, but cat or dog food left outside is absolute manna for rats. Keep the parking area clean and they’ll be more inclined to keep away.

So, watch out for tell-tale signs: droppings near the car, chewed engine covers or sound insulation are early warnings that wire hungry rodents are on the loose. Act quickly to put them off, or an ailing car and a big bill may be the result.

By Tim Shallcross, IAM RoadSmart’s head of technical policy and advice