MX-5 OC Forum

My 06/56 NC has developed what I think is corrosion under the paint on the bonnet (n/s rear corner). It looks like the corrosion is tracking like a little worm under the paint. The paint isn't broken at all... The car has only got 17k miles on it and has been mollycoddled from new and kept under a dust cover in a garage, and rarely driven in wet weather and always chammied after a wash!.. Has anyone else got this problem? I believe the bonnet is aluminium? How do I deal with this corrosion? I don't want to repaint the bonnet because the car is otherwise completely original and like new - in my experience re-paints never look like a factory finish... Thank you in anticipation!

 Yes alloy bonnet and frame. I'd take it to a good body shop. It's a single panel they can easily remove and prep/spray on a table and oven cure so you should expect a near perfect job without overspray etc. It also fits between the wings and nose cone which is usually slightly off in colour/finish due to being plastic so I really don't think the finished job will be noticable. 

If ally then oxidation... :-/ was hoping I might b able to cut/scrape back the affected paint and touch it in but I've only done that with steel panels so don't know if that would stop the oxidation. It's strange though as there is no break in the paint surface. I have to say the corrosion protection on the car generaly is rubbish. I dread to think what it would be like if I used it year round..

There is an interesting thread on MX5Life at the moment with a guy called Hamish putting right corrosion on his bonnet

 Check the warranty for corrosion that is coming from the inside outwards don't Mazda have an anti-preforation warranty for 7 years un sure about the number of years TBH may all hinge on wether the body warrnty checks have been carried out by a dealer I would suspect but it maybe worth a go and who know may save you some pennies

Alan

When you say it's covered in your garage... Is it a breathable cover? If not this could be the cause of your woes...

X66:

If ally then oxidation... :-/ was hoping I might b able to cut/scrape back the affected paint and touch it in but I've only done that with steel panels so don't know if that would stop the oxidation. It's strange though as there is no break in the paint surface. I have to say the corrosion protection on the car generaly is rubbish. I dread to think what it would be like if I used it year round..

Yes I've had "spiders" under the paint on another car and they usually come from the edge of the panel, mine came from the sill edges upwards, is the bonnet edge scraped or rubbed at that point?

Our car's a bit older than yours and I can see what you mean about the corrosion protection. Visually, there's not much on the underside and the edges of the metalwork starts to look dry and flaky after a few years. Most cars are like that at 6 years old though.

After a good look round ours it was clear there was nothing serious and the car would most likely manage its 12 year perforation warranty ok. The paint warranty is 3 years for external surfaces. Trouble is that it's hard to go back after corrosion has taken place so we had it Dinitrol'd which is relatively cheap and should now extend the life to however long we keep it given that it's a w/e car.

This is a big improvement on two Mk2s we went to view which both had rust-through on the sills and wings at 8-9 years old.   

 Alas, the warranty won't cover it because there is no perforation of the metal. I guess I am just upset because I have worked very hard to keep the car in 'as new' condition... The dust cover I keep on it in the garage is a high quality breathable one from MX5 Parts UK. The paint work is otherwise completely unmarked apart from a couple of tiny stone chips. There is no break in the paint surface anywhere near the corrosion 'spider' so I don't understand where it has come from. I have always been fastidious about drying it off after washing it and since its first year it has never been driven in the wet! I even used the supplying dealers lift to get underneath it to give the whole underside a thorough coat of waxoyl before the car was a month old...

Yes a bit of a shame if you've had it that long, and not in warranty as you say. It must just be bad luck but it will still be in great condition if you've cared for it that way. I'd definitely get it fixed professionally if you want to keep it, you'll be on a hiding to nothing trying to fix it yourself in such an obvious position and without modern paint