I just got a 2012 Base, 75k miles, one previous owner. It was kept in Tennessee but is now in Wisconsin. It has, as per my mechanic who inspected it, extraordinarily little rust, he could tell immediately that it was kept in a state that doesn't regularly salt roads.

This is going to be my third Wisconsin winter but the first two were with a 2004 almost 300k mile Civic that was already pretty far gone. Now I have a car that I care deeply about keeping as long as possible, to the point where I'm willing to incur the cost of a weekly wash if that's the most effective way.

Should I get undercoat applied or just stick to frequent car wash trips? I've seen a lot of mixed opinions on this - including something claiming undercoating is obsolete on modern cars. Does this apply to the materials used on the Fit? I have already been told that if I do washes it should be as soon as possible when it gets above 32F when the roads have been salted.

 

Cars (daily) driven in winter salt conditions will rust. All you can do is slow it down as much as possible.

Products like Fluid Film, Woolwax, or Blaster Surface Shield are well reviewed (plenty of good long-term videos on Youtube) and do seem to help. I spent many hours removing all the underbody panels/shields, fender liners, etc., cleaning the undercarriage and suspension, and then applying Surface Shield to the 2014 Nissan Leaf that we bought in 2021. We use the Leaf for all local driving, including throughout the winter. It's a lifelong Massachusetts car and they love salt here, so it was a bit rusty underneath when we got it. After the Surface Shield (and see below) it hasn't gotten noticeably worse during our ownership.

I also (hand) wash the car as often as I can in the winter, paying special attention to rinse off the undercarriage and flush the different areas that trap gunk and salt. It is very helpful to use plastic ramps to (alternately) get the front and rear up in the air a bit to make it easier to get to the undercarriage. I also have an electric pressure washer and foam cannon which make the job a bit easier.

Because we have the Leaf, our Fit is a long trip/highway-only car, meaning I don't drive it in the winter unless I absolutely have to. If I do drive it, I wash it afterwards as soon as the temperature hits anything above freezing. Yes, that sucks when it's 33F and I can't feel my fingers, but I have a 2010 Fit Sport with no undercarriage rust so it's worth it for me.

If you live in town and have access to a reasonably priced carwash that would be a good alternative and (much) better than not doing anything.

 

@Sabbagels It's a good question. I wish I had a good answer. I'll follow this thread. Maybe the smart guys here can educate me.

 

It's a car. Have it treated for rust every year and drive it. Also, a good wash/wax 3-4 times a year is required to keep it looking good. You can also put some mineral oil around the windshield to prevent rust from forming there, maybe once every 2-3 years.

Doing that, I was able to keep my cars for ~20 years / 250k km with minimal rust. And I'm in Canada, where we have lot of snow and they use lot of salt on the roads.

If you really, really don't want your car to rust, don't drive it in the winter. Buy a beater car for the winter...

In the end, it's just a car meant to be driven!

 

Personally, I think that the anti-rust can help a little but nothing beats frequent washing, especially in winter with salt. Modern products already protect better than on old cars. If I were you, I would especially do a regular washing of the underside as soon as possible after the snow.

 

I got a membership to the car wash down the street for this very reason. A lot of people around here (NE Ohio) do oil undercoating. There's a spot nearby that does only that and the line runs down the street around this time of year.

 

Based on what I have seen of the Fit's factory rust prevention, I would get a comprehensive application of something (anything) before your first winter.

I've lived in the salt belt my whole life. In general, "newer" cars are much better than "older" cars, but the Fit's price point in the Honda lineup leaves it with almost no protection (on the underside at least) and it might as well be the 80s or 90s. When my family was shopping for our Fit, they were all noticeably rusty underneath unless they were only a year or two old. The undersides of older, much higher mileage Toyotas (Camrys and SIenna) and any German cars are spotless by comparison. There's enough rust on the Fit we ended up purchasing that it adds complication to repairs and maintenance. It's not falling apart but at every turn you're planning for things being stuck, rounding off, flaking apart etc...

If there's one thing I wish, it was that the previous owner did Krown, Rust Check, or crawled under with a couple rattle cans of Fluid Film when it was newer. Years ago I used Krown more or less annually on my 90 Integra and in the 2000s I had mechanics coming out to tell me how great it was to work on because it stayed rust free. I've gone all DIY since then, so the hassles of wrenching on rusty cars are all mine now.

 

I've seen a lot of Fits where the rear wheelwells get rusted out first, in the part of the curve behind the rear doors. Or could it it be more of a First Gen thing? At any rate, by the time its visible there its probably also pretty badly rusted underneath as well.

I got lucky with mine, buying it at 21K miles and it was real clean underneath. I drive a lot in the winter but I also spray a LOT of Surface Shield under and around everywhere I can reach, including inside the rocker panels. So far so good. The use a LOT of salt where I live so I am trying to stay ahead of the rust.

 

Yes, I have seen a lot of 1st and 2nd gen Fits with rear fender issues forward of the rear wheels. The 2nd gen Fit we purchased has just revealed rust here too after this past winter, despite what I started doing (too late in its life) to try to hold it at bay. In general, my post is not about body rust you'll see topside, it's about what is ravaging underneath where you can't see unless you wrench on these cars yourself. It comes around the fenders and skirts after it's been eating at all the stuff you can't see for years. What you see rearing its head from a casual glance is just the tip of the iceberg.

 

I live in a couple of snow events per year location (SW Ohio). I go pretty overboard on underbody washes after snow events. To date I have been able to keep my 2013’s underbody rust to a minimum (With the exception of a catalytic converter heat shield I had to replace). My impression is the rust protection on the 2013 Fit is better than a 2003 Accord I had.

 

Is there a way to stop/slow down areas that are rusting with some sort of application? Heard Rust Mort is effective...

 

Sure. If you can block oxygen from reaching the surface you stop oxidation. If you block moisture and "accelerants" such as salt from reaching the surface, you slow rust.

There are dozens and dozens of products that purport to do that, including products that claim to convert the rust to a non-reactive form such as the Rust Mort you mentioned.

There are other products that coat the rust with a compound that claims to drive away moisture and block further oxidation, such as Fluid Film, Woolwax, Surface Shield, cavity wax, etc.

Or, there's the old redneck approach of smearing some grease on it. Most rednecks have a ready supply of grease on their person for just such an occasion.

All of these approaches assume that the rust you can see is caused by damage to the surface you can see and treat. It's more common that the rust you see (e.g., on a rocker panel) started on the interior of the panel and has been eating through the panel before finally appearing on the exterior. In that case, nothing you do to the exterior rust or the exterior of the panel is really going to help.