Project BMW MINI One
Do BMW MINIs rust as badly as classic Minis? Rob Hawkins assesses the corrosion on our project car and decides to take action, just in case!
Cars these days may not rust like they used to, but there’s no point taking chances so Rob nips any problems in the bud.
Had I been working on a classic Mini, waiting 20 years to think about rustproofing it would have been far too late. In the case of the BMW MINI One, whilst corrosion isn’t going to be a problem at present, it’s worthwhile planning ahead and assuming that any surface corrosion won’t go away.
I missed an opportunity in the last issue of Classics when the MINI One went to mad4mini to have its subframe removed and front lower arm bushes replaced. If time had allowed, I could have cleaned and painted the subframe, but realistically, that takes a couple of days, meaning one of their ramps would have been out of action. At home in my garage, I have the luxury of more time, so I can leave paint, rust inhibitors, waxes and underseals to fully dry for a day before applying the next coats. Rustproofing is never a quick job, and treating the mere surface corrosion on the underside of the MINI took five or six hours to complete, spread over four days.
Having the advantage of an inspection pit in my garage made the job of rustproofing the underside of the MINI very straightforward. I’ve spent many an hour laid on my back with a car raised on axle stands and drive- on ramps. Not anymore. Standing upright in an inspection pit means I can safely work with an angle grinder and wire brush to remove dirt and surface corrosion.
I used a rust inhibitor to treat any remaining surface corrosion that couldn’t be physically removed. This turns the iron oxide to iron tannate and helps to form a seal that prevents further rust occurring. However, it also acts as a primer, so needs to be painted. I used a stonechip paint for this. In some cases I decided to add a further layer of rustproofing, either in the form of underseal or a lanolin-based solution called Prolan, which helps to provide a waterproof barrier. And where areas are inaccessible, such as inside chassis legs, I applied a thin coat of
Hammerite Waxoyl to help repel moisture, although water should drain out of the many holes along these structural parts of the bodywork anyway.
The condition of the underside of the MINI seems to be pretty good. The worst patch of corrosion I found was at the backs of the sills, close to the rear wheelarches. This area is partly concealed by a plastic trim panel, so I tried to remove it, only to discover some of the fastenings had seized, so they had to be destroyed with an electric drill and replaced. Once I had
better access to the sill area, I realised the corrosion was only superficial and could be treated in the same manner as the rest of the surface rust I’d found.
One aspect of the underside that did initially concern me was the petrol tank straps. These were coated in flaky rust when I first inspected them, so I partly detached them (they are routed over the exhaust system in a saddle design) to be able to clean and treat both sides. After scrubbing them with a wire brush, I applied a rust inhibitor, followed by a stonechip paint and finally a coat of Prolan. The lanolin in Prolan is sourced from sheep, so the underside of the MINI did smell like a farmyard for a few hours, but that seems to have worn off now.
One area of potential corrosion I needed to address concerned the boot. The boot floor had filled up with water, so I wanted to drain this, treat any corrosion, and then find and fix the source of the water ingress. With the boot emptied, I removed the plastic undertray, prised out a few drain plugs and had a drain tray at the ready. The water ran out, allowing me to dry the boot floor and breathe a sigh of relief at the lack of corrosion. Even the exposed area of boot floor was rust-free.
Next, I had to find the source of the water leak. There are a few common causes, including the high-level brake light, tailgate seal and plinth, and the rear wiper. I discovered the tailgate seal was damp, especially around the middle bottom edge. Could water be leaking past
the components above it, which include the wiper, plinth and brake light? There was only one way to find out, so I removed each one in turn, checked any seals or gaskets, cleaned away all traces of dirt and refitted parts or resealed them where possible with rubber grease that helps keep rubber seals supple.
I wish it was that easy. The high-level brake light wasn’t too difficult to remove, secured with Torx T20 screws. I found lots of mould inside, so water has been trapped, but has it leaked down into the boot? I’m not sure.
The plinth was similarly easy to remove, clean and reseal. This time I could see how water could leak past the holes in the tailgate where the wiring for the rear registration-plate lights is routed, so I sealed these areas with a little grease. It may help, but I’ll have to wait to find out.
As for the rear wiper, after removing the trim panel on the inside of the tailgate, I wondered whether it would help to remove the motor and wiper arm to reseal it, but realised the wiper arm was seized onto the motor’s spindle. Penetrating fluid didn’t help, so I’ll have to leave this job for now and see how things progress.
Fixing water ingress in the boot isn’t straightforward because I don’t know how long it took for the water to collect inside. Thankfully, we’ve had plenty of rain where I live, and the MINI has been back outside on the driveway. So far, so good, and the boot floor has remained bone dry. Or have I spoken too soon?