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Undersealing / Rustproofing 66 Coupe

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    Undersealing / Rustproofing 66 Coupe

    I'm picking up my car this weekend and already thinking about protecting the underside.

    The car has lived in Los Angeles it's whole life and it still has the factory under seal, albeit this is flaking a little in places. The paint is still absolutely perfect under the sealant and although I will strip this back I'm reluctant to then coat it in black goop to hide the originality of the bodywork.

    Any suggestions on how best to protect it? Clear Waxoyl? Dinitrol? As far as I could see on inspection there is absolutely no rust so I don't think its a case for POR15 or one of those other products that bind to the rust.

    I appreciate I will need to do doors and other cavities and I will be applying at home myself so looking for something user friendly.

    Guidance welcome, thanks!

    Hmm, Tricky one.
    Waxoyl leaves a nice sheen and is cheap and you can top up or clean off easily if you change your mind. Safe bet. Picks up the dirt though. Maybe something tougher for the wheel arches if car used in all weathers.
    I have a can of Dinitrol Corroheat which is a clear hard wax for the engine bay which is supposed to be quite tough. Maybe there is something similar for the chassis?
    Clear POR 15..but surface would need to be super clean and de-greased for it to stick.


      I used clear wax oyl, and check/reapply if required on an annual basis.
      That said I don't use it in winter and generally it only gets wet if I am caught in the rain.
      no rust so far!


        My opinion is that if the car survived 50 plus years without rusting and you are not going to be driving in the winter you leave it alone. Nothing cooler than original red oxide underneath

        If the current coating is flaking then I would spend some time clearing off the flakes which hold in the moisture

        When we do undercoat we use a shultz type product thinned out to not hide any of the detail of the floor. Like a thick coat of paint if that makes sense.

        The frame extensions and cills basically never rust unless exposed to serious salt. Cavity wax at the bottom of the doors may not be a bad idea but don't clog the drain holes. the front corners of the doors are the worst for rust as the drain holes were not sufficient there and if parked on a slope the water gathers there at the front corner
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          Frankly, in this country, I would give it some protection. The chances are you will get caught in some sort of weather whilst out with the car and the last thing you want is corrosion getting into any seams etc.
          Depending on how it looks, I might be tempted to simply apply a wax over the existing underseal etc. Removing any underseal you have currently will likely damage whatever is underneath. You must be sure it is absolutely clean and dry though, your call really. Dinitrol will tend to melt any existing underseal back to soft and will penetrate beneath any flaking if applied with a proper gun.
          My approach is to have the car exactly as I want it underneath, then cover with Dinitrol - either black 4941, which is incredibly good (but black), or Dinitrol HP which is stickier but clear. If for any reason I want to get back to the original finish, it will all come off with hard work and white spirit. Better protected than rusty, in my book.
          Whatever you do for the bits that show, it would be madness not to use a proper professional lance system to spray corrosion protection into the frame rails, sills and torque boxes. These won't even have got primer from the factory and even from a hot climate may have signs of corrosion from condensation. Nobody's ever going to see that, except with an endoscope, and it makes a real difference. It's not worth doing with aerosols or cheap underseal guns, you need something like a Sata cavity gun, or pay a corrosion expert to do it for you - maybe someone like Rustbuster? Don't know, I do my own.


            Excellent thorough advice, thank you. I'm going to crawl under it this weekend and assess properly in light of this.I'll post some pictures up too.