Oh and the malibu rust did start right around those fender skirts and grew insanely fast, it went from a beautiful car into a rust bucket in record time.

 

i am a beleiver in a good factory undercoating, the one on my buick kept the frame, floors & rockers just as solid as the day they were sprayed with undercoating at the factory.... in 1965. so thats about 40 years and 92,000 miles on SALTY NJ roads. pretty amazing stuff.

on the other hand, my uncle had a mint '74 buick la sabre convertable with NO rot that he did a quickie resto on... paint, interior, top, and he insisted on getting an undercoating done... well the undercoat actaully sealed in the little bit of moisture on the frame & floors, and the car rotted out WITHOUT the aid of salty roads in about a year and a half. which was sad.

IMO, washing the car off is the best way to prevent rot. a friend's dad had a '91 S10 he bought new, and made sure to wash the undercarrage religiously. he sold it with almost 250k miles on it, and the body was still really nice.

 

I don't think undercoating would be a bad idea. My 05 that I bought used is already rusting on the frame and core support. My car lived it's whole life in Belvidere IL and was driven on the highway (basically getting salt/sand blasted) - I wish the previous owner spent some time to under coat it. In the spring I have to get the door seams fixed because they too are starting to bubble (especially the passenger's side door).

 

You are all making me feel guilty for only washing my car in the winter about once a month. Live in southeastern PA -- and salt is definitely used in my semi-rural area. So, far my 2005 car doesn't have any visible rust....but now I want to rush out and crawl underneath it.

 

Undercoating is good to do on a new car with a pristine undercarriage. Mostly its good for keeping stones from chipping the factory primer off of the undercarriage which can be a beginning point for rust. If you have already driven the car for a while, or there is already rust on the undercarriage, I wouldnt recommend it because it can actually seal in moisture over the rusty metal and speed up the rust. Thats what I have noticed, but some people may have different results with undercoating. It really all depends on the condition of the undercarriage before application, the quality of the undercoating and application and the environment that the car endures.