We've had major problems with mice in the engine compartment of the 2500hd (gm). They nest in the large fuse box, eat fuse plastic(!), eat the. Black insulation skin, and rip out the glass wool to make nests throughout engine (and, inside air filter box). I used snap traps for two years, and caught many (so many, i stopped counting). And, that was during the summer/fall season (6 months). The other six months the rig was stored in a marina heated facility.
This winter, we are storing at our house outdoors. I separated truck from camper, and parked truck 40 feet from where mice invaded it (truck now out in middle of driveway, far from forest, and our dry stacked stone wall). So far, so good. Our snow hit in october this year, and no mice. I did build a custom steel piece (out of an old gm air filter mesh), and have installed it in the air filter intake to block mice (i remove it and put filter back when i start the truck). This summer, i will replace the black insulation (my dealer will do this for $237).
Research vegetable additive plastics and wire insulation. This is a major issue with at least 7 vehicle manufacturers and numerous of their models, today.
*drier sheets were absolutely useless. I tried 4 brands, and all of them were used by our mice, shredded, and made into nests! Also, the problem with volatiles like peppermint, and many other odiferous deterrents is that in open air, the effectiveness degrades, as the wind over your engine (with hood closed) or excess air movement oxidizes those agents in hours or a few days. Btw: mice create scent trails, and more aggresive mice will often encroach weaker holed up mice, and scare them off, whereby even more aggressive mice will displace those (a vicious cycle, following those scent trails throughout you engine, the scent lasting up to several years, unless you steam clean your engine...every few weeks.
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2004 Chevy Silverado 2500HD 4x4 6.0L Ext/LB Tow Package 4L80E Michelin AT2s| Outfitter Caribou