Yep its a known area behind those arch liners.

 

My 156 rusted that way but worse. I used zinc paint which I believed was a better long term solution...

 

oh, that isn't bad at all! id avoid waxoyl though, its an ancient product that will more often than not trap moisture and grit against the metal and rapidly accelerate further rust, and hide it until its too late. have a look into higher performance alternatives like dinitrol, lanolin based waxes like bilt hamber dynax, or zinc filled epoxy coatings

 

On my previous Giulietta I was recommended lanoguard by the specialist I use, as it goes on clear so it doesn’t hide any creeping corrosion.
That car had a little surface rust behind the rear arch liners on the outside face of the rear door shut and on the rear ends of the inner sills. I didn’t get around to it though as the car was written off shortly after, so I can’t say how good that product is.

 

Unfortunately lab tests have shown lanoguard isn’t as effective as it should be. Dynax is the same concept (lanolin based wax) but seems to be much higher performing in tests. I’ve used both in the past, and whilst lanoguard won’t make rust worse like some options, it isn’t my weapon of choice anymore

 

All steel cars rust eventually. The Giulietta along with the MiTo have proven very rust resistant, especially when compared to previous cars such as the 159, 156, 147 and GT.

 

I've used all sorts over the years. Started off with waxoyl on my fiat Uno (a long time ago!), more recently dinitrol on the Brera and now Krown. I've found that anything which claims to dry to a non-tacky film eventually cracks and lets moisture in. Dinitrol underbody black wax has done this on my Brera where I applied it along seam joints and now wish I hadn't.The only solution I can see is to apply something that stays wet or sticky and keep applying regularly.

 

9 years in the Highlands of Scotland...And it's the area between the rear axle and the read end that is affected. The salt in the road grit got the best of it. The front looks good.

I've been recommended either clean up & powder coating of all suspension elements and body/chassis, or a clean-up and Dinitrol treatment carried as below:

 

clean up and KLine + dinitrol or stuff like that

 

I tackled the other side today. Everything is good up front, just the rear. There are some very difficult to get to areas such as the mounting count outs for the rear trailing arms. When these companies say clean up and rust removal, I can't see how that possible unless they mean using rust converter. The surface rust creeps under the thick seam sealer which can't be got at. I noticed the seat belt anchorage bolts were desintigrating. I've sprayed this area with dinitrol rc900, primer then Krown followed by some hammerite underseal. Not pretty, but will hopefully keep the worst at bay for a year or 2. Done the same around the spring mount and chassis leg. Also noticed the boot floor and rear back panel (behind the lower bumper) flakey. Tank straps not great either.

 

Yes, they do rust - mine failed an MOT due to it and needed a bit of welding.

Nothing like as much as my old Ford Puma and SportKa required tho - with those cars I assumed and budgeted for welding at every MOT!