# Undercoating for cars **URL:** \ **Category:** In My Humble Opinion\ **Created:** [May 24, 2023, 1:25am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487 "2023-05-24T01:25:44Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [May 24, 2023, 1:25am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/1 "2023-05-24T01:25:44Z")
Now that I live in snowland, we have to deal with salt on the roads. One friend says he always has undercoating done but another says that the chances are higher we’ll total the car first by hitting a deer before it rusts out. It’s past the end of the snow season for this year, but some people say this is the time to have undercoating done. Looking online gives both views by very confident looking people. As I’m not really a car person, what say the teeming masses? (I wasn’t sure if this or IMHO was a better fit. It can be moved if needed.) ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [May 24, 2023, 1:27am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/2 "2023-05-24T01:27:56Z")
How old and valuable is the car? ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [May 24, 2023, 1:30am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/3 "2023-05-24T01:30:09Z")
It’s a used Toyota Estima minivan, maybe $9,000, but we don’t have the budget to replace it very often. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [May 24, 2023, 1:37am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/4 "2023-05-24T01:37:23Z")
Googling, Consumer Reports advises against it, arguing that the corrosion protection provided by the manufacturer makes it unnecessary. (And I vaguely remember them arguing that in applying the aftermarket undercoating, the dealer might drill holes in the car, and those holes can be the start of rusting.) ---
**Author:** ![snowthx](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snowthx/32/10660_2.png) [@snowthx](https://boards.straightdope.com/u/snowthx)\ **Post date:** [May 24, 2023, 1:46am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/5 "2023-05-24T01:46:18Z")
> [@TokyoBayer](#): > > Looking online gives both views by very confident looking people. Is one of those people named Jerry Lundegaard? ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [May 24, 2023, 1:47am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/6 "2023-05-24T01:47:16Z")
On a brand new car, it’s pretty much always an unnecessary addition that dealerships use to jack up prices. Parts designed to be exposed on the underside of a car are manufactured with a weather-resistant coating already. On used and owned cars that have gotten some years of use OTOH, it may or may not be worth it. Main problem is it has to be very thorough, and it needs to be re-applied periodically. Is the cost of getting it done every year or two to gain a few years of good condition worth it against the ever declining value of the vehicle? Unless you plan on driving it until it won’t drive no more, I’m guessing probably not. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [May 24, 2023, 2:09am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/7 "2023-05-24T02:09:24Z")
Undercoating hasn’t been relevant for two decades. Don’t bother, it’s a waste of money. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [May 24, 2023, 2:24am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/8 "2023-05-24T02:24:22Z")
Do you have an owner’s manual? The owner’s manual for my 20 year old car specifically says that no undercoating is needed, or advised. Undercoating can trap moisture and cause the very problem it is supposed to fix. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 24, 2023, 10:15am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/9 "2023-05-24T10:15:30Z")
I’ve heard some people spray the car’s underside with oil themselves, and then drive it on a dusty road. I don’t know if it does them any good or not. For agricultural equipment, there are products that leave a clinging oily film with a tendency to spread, penetrate, stay on the metal, and exclude water and rust. A favorite one is called “Fluid Film” and consists of wool wax, the heavy oil that comes from sheep’s wool, primarily consisting of lanolin. I use this on my tractor and attachments. I’ve also used it a bit in my shop. I buy it in spray cans but it also comes in cans like housepaint does. I’ve only been using it a few years, but have not found any new rust on anything I’ve been treating with it. It does cling. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [May 24, 2023, 10:52am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/10 "2023-05-24T10:52:33Z")
> [@Napier](#): > > I’ve heard some people spray the car’s underside with oil themselves, and then drive it on a dusty road. I don’t know if it does them any good or not. Project Farm > **[Best Car Undercoating? Let's find out! Is Flex Seal the Best Rust &...](https://www.youtube.com/watch?v=lyWHF4NoNVk%2F)** > > FLEX SEAL, WD-40 Specialist Long Term Corrosion Inhibitor, Fluid Film, Corrosion X HD, CRC Heavy Duty Corrosion Inhibitor, Corrosion Block, and used motor oi... Motor oil at 6:55 ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [May 24, 2023, 12:39pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/11 "2023-05-24T12:39:40Z")
> [@Telemark](#): > > Undercoating hasn’t been relevant for two decades. Don’t bother, it’s a waste of money. Agree. I live in snow, snow, snow land. The salt and mag chloride kills the trees. But has never hurt one of my cars. I drive my cars for at least 10 years. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [May 24, 2023, 12:56pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/12 "2023-05-24T12:56:56Z")
I haven’t had a new car dealer even _try_ to sell me undercoating since my first new car purchase in 1982, when I fell for the “Rusty Jones” pitch. Even the dealers in upstate New York and Wisconsin. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [May 24, 2023, 1:15pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/13 "2023-05-24T13:15:28Z")
> [@TokyoBayer](#): > > (I wasn’t sure if this or IMHO was a better fit. It can be moved if needed.) Let’s move it to IMHO (from FQ). That will allow for personal anecdotes and experiences in addition to any factual information. ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [May 24, 2023, 1:55pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/14 "2023-05-24T13:55:22Z")
Well I bought a used 2000 Ford Focus in about 2007 and in 2016 I sold the car because it was so badly rusted through that I considered it unsafe. So I probably should have undercoated it when I bought it. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 24, 2023, 2:09pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/15 "2023-05-24T14:09:31Z")
> [@Marvin\_the\_Martian](#): > > I haven’t had a new car dealer even _try_ to sell me undercoating since my first new car purchase in 1982, when I fell for the “Rusty Jones” pitch. Even the dealers in upstate New York and Wisconsin. Same here. First new car I bought around 1980. They were pushing me to use their financing but I got a better rate from a bank. That’s when they remembered I really should get that undercoating done, but luckily I could just add the cost to the money down [head pounding against the wall emoji]. ---
**Author:** ![Tride](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tride/32/13907_2.png) [@Tride](https://boards.straightdope.com/u/Tride)\ **Post date:** [May 24, 2023, 2:13pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/16 "2023-05-24T14:13:58Z")
It also depends where you are. Lots of places are transitioning away from salt to mag chloride (still corrosive, but less so) or beet juice (non corrosive AFAIK). My 2010 Dodge 1500 has lived in CO and MT and only has a tiny bit of rust. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [May 25, 2023, 9:01pm UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/17 "2023-05-25T21:01:56Z")
Undercoating can also hurt the resale value of a car, because it is sometimes used to hide rust and other problems. ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [May 27, 2023, 5:28am UTC](https://boards.straightdope.com/t/undercoating-for-cars/984487/18 "2023-05-27T05:28:26Z")
Thanks everyone for your input. I’m still looking into it. I’ll ask the natives as well. > [@Tride](#): > > It also depends where you are. Lots of places are transitioning away from salt to mag chloride (still corrosive, but less so) or beet juice (non corrosive AFAIK). My 2010 Dodge 1500 has lived in CO and MT and only has a tiny bit of rust. Here in Hokkaido, they seem to be using the most corrosive salt they can find. Lots of our neighbors have rust spots around the wheel wells and along the bottoms of the body panels. Where we go skiing / snowboarding, they seem to salt the roads if it’s cloudy, let along snowing (OK, a bit of an exaggeration) but one of my friends has a hole in the bottom of his car from where it’s rusted through. Our used mini-van is 12 years old, with only 60 k miles, and we plan on running it into the ground or until repairs start to get more expensive than replacing it with another used car. I’m not worried about the resale value. Anyway, thanks everyone for their input and I’ll do some more research. They recommend doing the undercoat in October if we do it, so I’ve got some time.