When I was under my car the drainage tubes did not go into the sills. !!!
Its not going to get better. It might just need a section of outer panel cutting out, and new metal put in, or, once you dig into it, there may be damage to the inner sill. The cost of the repair will likely rise the longer it is left. Remember, its rusting from the inside out, so what you see is literally the tip of the iceberg.
Mk2.5s had a 6 year warranty.
what if i clear the drainage holes and spray the critical areas with hammerite. It will not make it any better but would stop the rusting process would it not (assuming the inside is not rotting yet and it’s only the outer sills)?
As stated above, its rusting from the INSIDE out, so there is little point in painting the outside with Hammerite. You could spray the inside with a rust preventative, but the eventual repairer will not thank you for making his job harder. I nearly set a car on fire when the rust inhibitor I had previously sprayed into a sill caught fire during subsequent welding. The longer its left, the more expensive it will be to fix.
Alan
I would recommend cutting off the outer skin and replacing it, repairing anything found inside at the same time, have a look at my website, we have done many repairs just like that, my advice would be to get it done as soon as you can afford to do it
Conditional on having all the inspections…
Of course, but the duration is an indication of how much confidence the manufacturer has in their product. Mercedes now offer a 30 year body guarentee.
It’s not a big deal to combine an inspection with the annual service. Surprising how many people don’t bother though - which affects their car’s resale value.
This give you an idea of the paint inspection:
http://www.mx5scotland.co.uk/board/viewtopic.php?f=6&t=8599
In truth, if they spot rusting, they’ll rub down, repaint, and that will probably look ok for the balance of the warranty, and then the big holes appear.
I don’t think Mazda make repair patch panels, so instead they will have to replace the entire rear wing. Hence wriggling.
The Mazda 6 year warranty on the bodywork (for my 2.5) was an anti-perforation warranty rather than an anti-rust warranty and actually excludes damage due to corrosion caused by salt - so they probably would never have paid out for any repair even if it had become apparent during the warranty period. The dealer I bought the car from never suggested that I have the annual check - they did the first one automatically with the first major service and I suppose I assumed that it was included as a service item rather than having to be specifically asked for - I later noticed the lack of stamps in my service record.
I guess I was lucky in that the rust on my car became apparent after 10 years - sills just repaired last week by The MX5 Restorer at £250 per side (3 days) - looks good and I hope it’s going to last well - Garath did point out several other areas that will need attention soon though.
I’m reading these threads with some interest. Our Mk1 97 Classic has the same sill rust problem. I’ve bought some rear sill sections off eBay which are slightly thicker gauge but like many people have said its the rot from inside out that needs to be tackled first.
My plan is to remove the rear end of the sill, cut, repair clean as must as I can and then paint with zinga - 96% zinc protection paint, then refit the outer skin repair sill. Seeing the cross section, I then plan to flood the sections with rust prevention liquid - haven’t decided what yet. Then repaint " For me the problem is the double skin and the trap the rear sill section has - maybe it needs a 3rd drain hole for this double skin section. It woont be any worst than what’s there already? Maybe!if I think the repair is sound I’ll post the stages I go through with pics.
Regards
namb
Best of luck with the repairs and let us know how it turns out 
I don’t suppose deliberately feeding rainwater (and perhaps with it some pollution therein) into mild steel inner cills from the rain rail has helped any 5 of any vintage. As for galvanising, I recall seeing a brochure insert that was distributed to dealers many years ago showing an exploded view of Mk2 panels and those that were supposedly zinc coated.They were nothing of the sort of course, and these brochure inserts were withdrawn.
I see plenty so called prestige cars of similar ages rotting away merrily…especially Mercs & BMWs. Cannot help but notice the rear arches of many other Mazda models going to seed. I guess good old British winter salting + mild steel is always going to be an issue.My Dad used to coat all his Poxhalls ,and Beetles in old engine oil through the 50’s & 60’s and as far as I know, they remained rock solid. Let’s face it, cars are made to squeeze through warranty periods…after that why should the maker really care? I think the required “body inspections” at dealers is just another cash cow “hook” to keep people in fear of going anywhere else for services. Mind you, is it not the case now that owners are entitled to go elsewhere without damaging their consumer rights? Nice touch from Mazda to computerise Mk3/Mk3.5 service histories too. I’d prefer a hard copy please!
There’s lots of interesting stuff here about sill repair and the causes of corrosion. I’ve just had mine repaired and the experience made me wonder whether when buying a car it would be better to assume the work will need doing and budget accordingly for this. I paid top money for my NA about three years ago and, yes, it looked mint and was low mileage etc. But despite being garaged and only covering 10k miles since I bought it (almost only ever used in dry conditions) the sills were rusting from the inside just like any other mx5. I might have been better to buy a cheaper car and have it repaired from the outset. I’m putting my faith in a good quality repair with the sills now sprayed internally with waxoyl but only time will tell! My view is that while drain holes etc do need to kept clear perhaps an equally damaging thing that we can do little about is condensation within the panels due to humidity and temperature changes. Hopefully the cavity wax will prevent that from contacting the metal.
How do all the Eunos that come over have squeaky clean sills after 15 years and rust with 5 years of getting here?
We put so much salt onto our roads which finds its way into the inner cavities and it combines with condensation and other dampness which cannot escape from the rust-prone areas.