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MG MGA - rust on inside of bumper

While I was under the car yesterday I noticed some light surface rust on the inside of the rear bumper. The rear bumper is only 3 years old. Is there something I can use on it to stop it now before it gets any worse?
Kris Sorensen

Kris - I've been told - and do it myself - to paint the chrome bumpers inside and out with good old Dr. Diesel.
The diesel gets into any pores in the chrome and then the surface can be wiped clean. The inside rust will also be held at bay. Not expensive either. Cheers Brian
brian pollard

I have repro bumpers and they have rust on the inside . a wire brush and a can of aluminum paint did a great job. PS: My car is clean and origional but not perfrect. gordon
Gordon Harrison

>> I have repro bumpers...
>> My car is clean and origional...

Don't want to stir up a fuss, but aren't those two statements contradictory? :-)
Andy Bounsall

Hi Kris. I would use a powered wire wheelto remove the rust, then use phosphoric acid to neutralize any that remains in pitted areas. After all the rust is removed, I would coat the inside of the bumpers with a thin coating of heavy, sticky grease. This will prevent oxygen from reaching the metal, and should at least slow the rusing process. Cheers, Glenn

that's beacuse we use more salt in Quebec that Ottawa. So much it even effects my car when its stored in my garage LOL LOL.Gordon
Gordon Harrison

I'd use the phosphoric acid treatment like Glenn says, but then follow up with 2 coats of epoxy primer and some top coat.

Original bumper was painted on the inside. Clean it up and paint it again. Grease is messy and wont last.
R J Brown

I wire brushed my bumpers and and then gave them two coats of aircraft-grade zinc chromate primer, followed by a light sanding and two coats of semi-gloss black from a rattle can. It has held up perfectly for four years now.

You can order zinc chromate primer in rattle cans from Aircraft Spruce and Specialty Co. See:

Frank Nocera

Hi Randy. On the contrary, grease lasts extremely well, if it is thick and sticky. I used a thin coat of wheel bearing grease on the backside of my bumpers many years ago, and there is no trace of rust. Over time, a thick coating of dust and road grime coats the grease, which covers the raw grease, and prevents it from getting on one's hands. I know this method of rust protection is somewhat unorthodox, but it is extremely effective at preventing rust! I use grease on the underside of all my vehicles for the last 20 years, including my current Toyota Camry and my MGA. Before that, I relied on rubberized undercoating and dripless oil, neither of which were satisfactory for preventing rust. Grease adheres much better than undercoating or dripless oil, and lasts for many years. I simply brush on the grease, using an old paintbrush. I retouch the underside of my greased vehicles every few years, and am amazed by how little additional grease I have to add. Yes, grease is a bit messy, but I am convinced that it really is a most effective method of rust proofing. Any minor paint scrapes that penetrate to bare metal, and are covered with grease simply do not rust. Even light surface rust that is greased does not seem to get any worse. I still use dripless oil, which I spray inside the sills and pillars, and boxed in areas of my vehicles that I cannot reach to grease. I got turned on to greasing the vehicle underside by an English professor who drove a very old, and very rust free early Saab. I noticed his vehicle was rust free, although it was very old, and the paint was very faded. I asked him why his car wasn't rusted out, and he told me to look underneath. When I did, I could clearly see the layer of grease, which covered the entire underside of his Saab. His only instructions were to make sure to use a thin layer of thick grease, and to ensure that grease covered everything that was not intended to rust, excluding the exhaust system and rubber components, and to use extra grease on and being forced into welded seams. Cheers, GLenn

...AND it makes it so much easier to slide in under the car if you need to do some repairs. 8^)
Andy Bounsall

I'll go with Gordon on the protective qualities of grease. I've pulled well greased stuff out of crates on WW2 shipwrecks, and it was still clean of rust after more than 50 years in salt water.....
dominic clancy


You can also use the silver POR-15 paint. Wire bursh the surface and use a small brush to paint on.


Larry Hallanger

I've had good success in similar situations with spray-on "cold galvanizing" which is just zinc powder in an epoxy base it gives a matte grey finish that can be overcoated and has lasted well for me. Readily available in spray can at better parts stores or marine suppliers.
Tom Heath

Thanks for all your great ideas. I can see the benifits of the grease but I may lean toward the cleaner look of paint.

Kris Sorensen

Hi Kris. I must admit that the greased underside of my MGA looks like a dog's breakfast! On the other hand, it's not rusting out either. Good luck with your painting. Cheers, Glenn

This thread was discussed between 11/05/2007 and 17/05/2007

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