How frequently should I wash 4Runner underbody?

So I've been taking my 4Runner through the car wash about once a week and I always do the underbody spray. I do this because the top-side gets dirtied up frequently so surely the underside is, and I figure in particular when the snow and ice, and hence SALT, starts, I should do that to prevent rusting.

Well my father says I am getting the underside washed too much, that I should not be getting the underside washed once a week but more like once a month, because otherwise I will start to take the coating off the bottom (not sure if he meant the rust inhibitor coating or the paint itself now that I think about it). However, the impression I had is that road salt is murder on the underside, so you want to get it washed regularly.

So which of us is right? I have it scheduled to go in for Krown rustproofing next week.

 

I would do it once a week in the winter months with just plain water (hi pressure at the car wash)

 

I’d also go to a quarter wash once a month and get down yourself and wash it with the soap. The car wash while better nothing is not as good as what you can do by hand.

I don’t know much about krown but I’d be sure to get it redone each year also.

I see so many 4R, Tacoma, and any other frame vehicle rust bad here in MI with salt and too many on this forum. It’s really ashame.

All manufacturers could do a better job preserving these frames. But then we would not buy as many vehicles.

 

I've used Krown, fluid Film, and now Waxoyl, the first two will wash off at certain wear spots eventually and the under body car wash only accelerates the process. IMO I would leave the under body unwashed and let the undercoat do its job in protecting it. As a side note if you are getting Krown applied at one of the franchises they like to drill access holes in the sills, I would advise against this. The 4runner already has factory access holes at the bottom of the sills that give plenty of access with a wand sprayer. Drilling more holes seems to give rust a starting point.

 

For the guys that fluid film what do you do you do for winter driving? Do you wash underbody salt off? I know you take off fluid film doing that but seems like a catch 22 since you would think need to get salt off also.

I am pretty lucky that I can keep mine parked in winter with the fluid film on and use another car. But I get it for those of you driving your 4R in winter.

 

Well I don't know if they have that as an option for the underbody. They have different

Will say that to them about the access holes, thanks. I know up here, the salt will rust away the bodies of vehicles even, at least trucks. Cars seem to be more immune, but I see lots of trucks with the wheel wells rusted to high hell. So the road salt does murder on the bodies of trucks and SUVs, or at least body-on-frame ones. So with the coating then, I am thinking maybe get the vehicle's body washed once a week but the underside maybe once a month, and depending, maybe once right after major snowfalls where they salt the roads heavily?

 

On my 2012 Tacoma I would fluid film heavily in the fall and that stuff will stay on well into the spring with no issues. I would still go to the car wash with it to get the salt off the paint on the doors and panels but wouldn’t care about any under carriage wash if I’m covered in fluid film. That stuff will keep the salt off the metal so no need to worry. If you do go to the under carriage wash- the fluid film will not wash off. So totally up to you. If you’re fluid filmed- just go once a month or so.

I am new to the 4Runner world and just picked mine up a couple days ago. Did not get to spray wool wax in time up here in the Midwest, Salt is already on the road. So I just plan on going to the wash with the under carriage feature any day it’s above 32 degrees. You’ll be totally fine. Again my 2012 Tacoma lived it’s whole life in the Midwest with salt roads and was only fluid filmed the last few years. There was still no rust at all on the frame because I washed regularly.

 

If there is salt on the roads, some shops will do a salt wash before applying the coating. The Krown shop I am going to is going to do that.

 

Another option is a harder protectant like Amsoil Heavy-Duty Metal Protector. https://www.amsoil.com/p/heavy-duty-metal-protector-amhsc/
You'll need about 2 1/2 cans to properly treat a 4Runner.
I treated my 2019 when new and this Amsoil product has work well and is still 100% intact.
I did let the product cure for 12 hours - as per the directions.

Also - I have prepped vehicles in the past for coating and used marine "Salt-Away" to treat the frame and underbody.
It does an excellent job of removing salt.

$51 Salt-Away Concentrate Gallon (128 fl oz.)

https://www.amazon.com/Salt-Away-Pr...g-goods&sprefix=salt+away,sporting,283&sr=1-4

 

IF you haven't done any undercoating spray, I would wash the undercoating weekly if it is being exposed to wet salty road grime. Once you get the undercoating spray, I wouldn't wash down under until salt season is over.

 

I drove a municipal snowplow for 22 yrs. That means I drove on the saltiest, sloppiest roads in town getting to and from work. We were allowed to wash our personal vehicles in the heated wash rack. The under carriage of my '96 Silverado was power washed, by hand, on my hands and knees, after every snow storm when the roads dried up. Some storms may have taken 3 days for the roads to dry. I am a firm believer in hosing off the chassis when ever practical. 272,xxx miles on the old gal. Frame has surface rust but it is solid. I have never treated the chassis with any rust inhibitor. Lived all of its life in Wis. Pic was taken Sept. of 2021. I hope my 4R looks this good in 25 years.

Also OP, all of the paint on the under carriage is still intact. This is my 1st hand experience with hosing the bottom of my vehicle.

 

Thats a beautiful old pickup sir. Kudos to you on maintaining it so nicely all these years.

 

Thank you!! Was a labor of love keeping it this way.

May as well show the inside. Notice the big lever in the middle.

 

I would use woolwax much thicker than fluid film and you literally need to power wash it in the strongest setting to get it off

 

if it's bare, once per week at minimum. if you have fluid film or a similar product sprayed on, you don't want to wash that often since it will wash it off. i would do it more like once per month that way it lasts all winter

 

^^^^
This.

Coat your underside in Fluid Film or Wool Wax. Wool Wax actually recommends not aggressively spraying the underside during the winter with their coating applied using a high pressure wash. A light rinse with a garden hose is ok.

 

So many pedals & levers. No way that truck gets stolen by some punk kid today!!

 

wash frame once a week....come spring..go underneath...eye ball it...clean, and if needed, prime / repaint..

 

I have mine sprayed with Krown. Their FAQ says it doesn't wash off.

https://www.krown.com/en/faq/