Under carriage protectant, preserver ?

[48firetruck]

I've been cleaning 77 years worth of crud out my 42s undercarriage and frame. Is there any type of undercoating or chemical that can be sprayed on to preserve whats there and not make a mess? I'm not interested in paint or conventional undercoatings, looking for a rust inhibitor / sealer that's basically invisible when dry. Does such a chemical exist?

[INTMD8]

What I did on my 59 was soap/pressure wash and when dry, fluid film in all crevices/inaccessible areas and sprayed the rest with satin clear coat.

Doesn't drastically change the appearance and seals everything up.  Not sure if there is a better option than the satin clear if you want to keep it looking similar to how it is now.

[60eldo]

 Hi Jim, do you have a pic of the same, but the front end you can post for me, thanks Jon

[INTMD8]

I can take one, this is as far forward as I have at the moment.

[signart]

I have used this with great results on tools and antiques, protects leaves a great patina. Can be used as primer for a top coat or apply 3 coats of the neutralizer and leave it natural. If you have Mennard's $6-7 Wally gets about $8

[Jay Friedman]

.....I'm not interested in paint or conventional undercoatings.....

I know they don't look very nice, but I think chassis paint and especially undercoating are the best means of preventing undercarriage rust.  My '49 was heavily undercoated when new in Denver, and I'm convinced that is the reason the car is still here with virtually no rust underneath.

[fishnjim]

Keep it dry, free of grime, and you probably won't need anything and keeps it factory.   Anything you apply needs to come off at some point, so I avoid, if I can.   Usually the better it is, the harder to get off, otherwise, it'd fall off and wouldn't be any good.

If it's seen salt, then needs extra help, especially in the lap joints, crevices.   These are riveted frame era.   
Pressure washing may remove some paint from the underbody and cause more issues so be careful with that.   
There's a list of "treatments" a mile long.   I don't know that any of them have been tested for the real long term on frames.   The CRC SP-400 (mil spec) corrosion inhibitor I use on antiques lasts only a couple years according to the label and needs re-applied.  Not a good option here. 
You can treat the surface rust, but not very effectively with the body on.   For my money, a frame off, blasted and powder coated is best for long term, but won't be factory.
I've tried these water based eco friendly rust neutralizers/inhibitors and not impressed with results.   But those require dipping, where you need spray/brush apply.   Be careful of overspray on the painted surfaces with anything you choose.   Test on a unnoticeable area first.   Why risk it?
I have not used the Eastwood frame rust convertor stuff they claim lasts, but POR, et al make too.
I've been using the 3M spray undercoat on the new vehicles that aren't coated, and any work I've done on the '58 that needs to be re-undercoated.   Factory was the tar based stuff which isn't available.   It's a high build rubber and not transparent or smooth.   Truck(non-GM) has nine years with it now with no issues.   GM vehicles have advanced in terms of corrosion protection these days.  Wasn't even a science in '42.   GM uses parafin dipping on the frames now, but not a DIY project.

[60eldo]

  Thanks Jim,,,,looks great. Id leave it like that.

[Lexi]

I have not applied any rust inhibitor to my current vintage ride, I just keep it dry. I also never wash my car, (but keep it clean and polished). I have annually treated my daily drivers however, with Krown Rust control. It is an oil spray that is done once a year in the shop. I began using Krown when I remembered a conversation I had with the owner of a '59 "Turnpike Cruiser", (or similar model), in 1979. He was oil spraying his car with a reddish colored fluid. He had purchased the car when new, in Canada. I believe he said the liquid was an aircraft lubricant similar to transmission fluid. He had drilled all sorts of access holes to reach the hard to get spots. Once every fall he spent an afternoon treating his car for the winter season. This guy was indeed a mega car "freak" and an enthusiastic preserver. The array of tools, tiny hoses & injection apparatus he was using to treat the car was amazing. To me this offered proof that those willing to invest the time and energy would at least delay the planned obsolescence of their automobile. This car was his daily driver and was white in color. No sign of rust even along the rockers. Quite the sight in 1979 Canada for a 1950s daily driver to be rust free. It was also always driven all winter long to work as well. He said "Someday all rust prevention will be based on this". I always remembered this and began using Krown in the 1990s and have had no issues with my daily drivers.

Come to think of it, when was the last time you saw a vintage oil or grease covered part from a salvage yard that was rusty? Coating with oil makes sense, at least to me based on my experience. Yes, it is not perfect and it is messy, but nothing comes without a disadvantage. Seeing that immaculate white 1959 Ford was quite an eye opener, and a compelling case for oil spray as a preservative, when used as a film to coat metal surfaces, (a standard procedure in the machining industry). Clay/Lexi

[Mike Josephic CLC #3877]

I'm not completely sure what your goal is.  Allow me to post
a few comments and questions.

You want a rust control product that is "invisible" but want it to
protect the metal you've so nicely cleaned.  You don't want to use
a paint.  You value originality since the car has it's original finish.

1) I know of no product that would be "invisible" and provide any
degree of protection, especially if you're driving in winter weather
with ice melt products on the road (salt, magesium chloride, etc.).

2)  If originality is a concern, cars as they came from the factory
were painted as follows:  underbody in red oxide primer (2) chassis
components were black semi-gloss paint

3) Cars never came with undercoating from the factory.  Some
seam sealer was sprayed or brushed on in areas but undercoating,
if done, was a dealer add-on.

That's a summary as I see it.  What you must decide is what do you
value most (1) originality (2) protection or appearance (as you wish
it to be).

By the way, I spent 35 years in the chemical industry.

Good luck,

Mike

[Roger Zimmermann]

Maybe a clear wax would help to some extend. However, on surface rust I'm not sure if that product can help.

[Jeff Maltby 4194]

Zero Rust is user friendly having used it on my 49 frame.

https://www.zero-rust.com/zero-rust-products.html

[Dr. John T. Welch]

Explore the products by Noxudol

www.noxudolusa.com/our-products/

[Mike Josephic CLC #3877]

Nice idea, but the OP is looking for something that does
not leave a visible film.  This material (depending on which
varient) dries tan / brown / black.  Contains waxes, bitumen,
aromatic solvents.  For example, UM-1600 as recommend for
cars:

Color: Black
Consistency: High thixotropic
Type of film: Elastic
Density at 20° C: 1000 ± 40 kg/m³
Dry content: 70 ± 5 %
Solvents: White spirit
Film thickness: 0,5 â€" 1,5 mm

Reminds me a bit of what Ziebart has been using for the last
40 years or so.

Mike