Rust
Rust is the biggest killer of any car, and E30s are no different. As perfectly constructed as they are, the ravages of time can't be held back and your car will at some point develop the dreaded tin worm.
When the brown starts poking through, consult this guide to see just what horrors could lurk underneath...
Contents
Front Arches
After years of abuse from grit, mud and road salt, the front arches will turn crusty and bubbly. Because of the inner lip of the arch, rust will develop from the back and by the time it has bubbled through to the paintwork, it will be a nasty cancerous patch all around the edge of the arch.
Repair patches are still available, and new metal can be let in fairly simply if you know the repair procedure. However, it is essential to remove all traces of rust from this area as it will accelerate extremely quickly.
Front Wing
Aside from the arches, the front wings on E30s are also prone to rust at their lowest point, especially if a body kit is fitted. The smallest amount of bubbling will usually reveal that the entire mounting bolt area has rotted away, and that the wing is only being held in by two bolts on the inner arch.
While a repair panel can be fabricated, it might make more sense to replace the entire wing, since they are easily detachable.
Front Inner Wing
The Inner wing, especially the flitch that supports it, can rust from behind the plastic wheel arch guard, and go un-noticed for years. The only signs will be scabbing along the top edge of the wing where it's bolted, inside the bonnet. If you see rusting along that edge, get the wing off and inspect immediately.
The repair can be made in situ, as long as it hasn't spread to the bulkhead.
Front Suspension Turret
The inner wing sits on top of a much more sturdy metal plate which forms the base of the suspension turret. Over time, water seeps in between these two skins and rots out the turret from the inside out.
It is possible to cut out and repair the thin sheet metal, since this usually doesn't affect the structure of the turret itself, but if the crack spreads too far it weakens the strength of the inner wing.
Rear Arches
Like the front arches, the rears are prone to bubbling around the lip. However, the more complex double joint of the rear inner arch adds to the moisture trap, making a double skin of steel. If your outers are bubbling, it is almost guaranteed that the rust has eaten through to the inner arch as well.
Because of the way that bumpers are mounted to the E30, it is also possible for blistering to start at the very end of the arch, where the corner of the bumper starts. Blistering here is caused by bumpers being clumsily fitted, chipping the paintwork, which then festers for a few years. If you have rust here, question why the rear bumper was touched, and look for signs of rear collision damage.
Rear Inner Arch
The welded seam in the rear arch is a known water trap, especially considering all the spray thrown up by the wheels. Despite BMW's best efforts, the smallest hole in this seam will rapidly spread out to rot the inner wing where it enters the boot. Unfortunately for the owner, the water normally collects in the side "boxes" where your jack is stowed, and you'll only see it when you go to change your tyre. The rust will show up as orange water stains on the paintwork if you're lucky; if not you'll be seeing the asphalt from inside your boot.
It is possible to cut out and repair this rust, but it is never fun laying on your back trying to weld upwards. However, simple patch panels can be folded to repair simple holes, while entire inner arch sections are available if needed.
Sills
Sills on E30s get coatings of rubberised stonechip from the factory, but after 20 years of battering from the grit it's not surprising if one stone made it through to the metalwork. If it did, the rust will munch you an MOT fail very quickly.
Cars with bodykits, especially Tourings which came with skirts as standard, are big rust risks since the wet mud can sit behind the plastic and eat away the metal for years without being noticed. If you see the tiniest bubble of rust poking out from your bodykit, be prepared for a gaping wound underneath.
Full sills are available, and are held on with spot-welds that can be drilled out and replicated with plug welds if required. For smaller holes, a patch is usually sufficient.
Inner Sills
Scuttle
Roof
A rusty roof is the only spot on an E30 that is considered terminal. While any metal work can be chopped out and replaced, the immense effort required for roofwork makes any repair uneconomical at best, and a complete b*stard at worst.
Roof rust shows itself as tiny blisters on the roof surface, bubbling up from underneath. If you have these blisters, you will need to take off the headlining inside the car to confirm the extent of the rust, but be prepared for a shock. A lot of the rust in these cases comes from the sunroof, specifically the cassette mechanism that holds the sunroof in place.
Sunroof
Floor
The floors on E30s is usually fairly solid, but there are one or two spots where rust is guaranteed. These spots sit at the front corners of the floor, and look like little square cups. These are incorrectly called "jacking points", and any attempt to use them as such will cause serious damage to the floor of the car. Certain mechanics don't know this, so it's highly likely that your car will have been lifted from these cups at some point in their life.
As soon as this is done, any underseal around them will have been broken, allowing road salt in to munch away the metal. You won't know it until you start noticing your carpets are constantly wet, by which time it will be too late.
The best repair is to cut out all the bad metal and let in flat metal plates. There is absolutely no need to replicate the "jacking points", as you are guaranteeing more rust in the future.
Bulkhead
Bulkhead rust is most evident as water leaking down behind the glovebox (or pedal area on LHD cars), leading to orange staining. It should also be seen as a spreading crack underneath the fuse box (seen with fuse box removed).
This can be one of the most problematic repairs, since the wiring loom travels through this area, and cannot be removed without stripping the interior entirely. However, lots of small patches will allow you to slowly rebuild the holes left behind, but will require more exploratory cutting to find the true extent of the problem.
Boot
For the most part, the bootlid fitted to 2-door and 4-door Saloons is pretty sturdy, but the vertical part that fits between the rear lamps is covered by a plastic shroud. This shroud is a moisture trap, and water gathers behind and starts rusting the panel from behind. It's almost impossible to notice unless you see crumbling orange powder on the floor of the boot, at which point the plastic shroud should come off for an examination.
