I have an 01 4Runner sport I purchased from a dealership and they used rustoleum undercoat on the frame and parts of the undercarriage. I got the vehicle pre inspected at my mechanic before purchasing and they felt the frame and hammered it for weak spots checking it for rust. They told me everything was fine and the rust was minimum and the frame was solid. Now im looking online and everyone’s saying to not use rustoleum or rubberized undercoat on a vehicle that old. I’ve had the vehicle for a few months now and some of the undercoat is coming off and it’s showing a little surface rust nothing major. My question is should I just leave it? Or should I try to take the undercoat off and use a oil based product. Is it even possible to take the undercoat off?

Sorry for all the question guys I’m just a broke guy trying to keep my 4Runner as long as possible. I love this truck

Yeah it will probably keep coming off and leave pockets for water/salt to collect and rust. I'll make my recommendation, as I'm sure others will too.
Not sure what region you're in, but I'm in Massachusetts. My 3rd gen 4runner has about 380K on the chassis with no rust. I just coat it with WD-40 every year before they start salting the roads, I've been hitting it again in February, but not necessary really for me cause of my long acquired skin of coating, but I do it a 2nd time anyway. My undercarriage is black and solid. Just a $20 gallon of WD-40 is all it will take to keep it solid. The WD-40 will seep into all the fissures and lifting undercoating and protect it. Just keep it coated and you're good. I actually just coated mine yesterday and I took pics before to show how good the coating holds up.
Here's my write up on how to do it -
SEASONAL RUST PROOFING using WD-40 only

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That's what stinks with Rubberized undercoating is that on brand new steel it's not so bad. On old rusty steel it traps the moisture in and can actually speed up oxidation.


Like Dogtail suggested knock off what you can and use your rust proofing liquid of your choice to slow down oxidation

Many products will work. I myself prefer fluid film. Lots of people use different products with excellent success. :]

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Rubberized undercoating is BAD. Mr Eric O in Southmain auto also shows how bad it corrodes when water gets in. Frame is flexible and it twists and any solid coating will cracks allowing water to get in. Once it is in, it cannot come out and makes the perfect condition for corrosion: Moisture, oxygen and metal!

Apply a thin film of oil (penetrating oil is the best) before the winter starts.

Oh nice! I didn’t know I could actually coat over the rubberized undercoating, that’ll make everything so much easier. One last question so when I wash my car should I skip the undercarriage wash so the oil stays?
Good thing is I live in NC so it only snows about once a year here.

Yeah I saw that video also, I wish the dealership would of never used it in the first place.

Thanks for always helping a newbie like me Brillo! Much appreciated sir!

Sorry about the multiple posts still new to the forum. Don’t have all the controls and edits down.

You can coat over the rubberized undercoating but some of the moisture will still be trapped between the steel and the coating. The good news is your in the south so no salt to deal with. Not as harsh as environment.

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