Rust treatment for rear wheel arches

[notsofast]

The rear arches of my 320i aren't rusty (in fact they're almost pristine ) and I want to keep them that way.

I'm thinkin' of a spot of preventive rust treatment - somethin' along the lines of waxoyl and/or underseal. What would you use for those arches?

What sort of prep would I need other than just giving those arches a good ole jet wash?

And how do you get the waxoyl into the inner sills?

BTW, I bought this old school 320i a month ago following buying tips from zoners. I've done nearly 1k miles since and I'm lovin it . Over Easter, I had the nsr wheel stuck in a gravel trap (a deceptively deep bank of gravel in a seaside carpark at Camber Sands). That arch took a helluva gravel blasting before I managed to get free with the help of 3 pushers and a lota gravel digging! No more seaside car park for me for a long while, that's for sure! The stone-chip paint insider the arch seems to be undamaged but I'm taking no chances. A little TLC is in order.

Thanks in advance.

[Jos]

The undersealer on BMWs is pretty good, the problem spots are up where the outer arch meets the inner wheelhouse, these trap dirt and crap which soaks and holds the water. If you can keep those bits clean you shouldn't have too many problems.

Waxoyl is a self repairing wax and imo shouldn't be used as the sole protection underneath, get a good rubber based undersealer and put a coat of it on 1st, then Waxoyl over the top of it. Just ensure the surface is dry and dirt free before starting.

Good undersealers are available from 3M, Tectyl and Dinitrol. They all have ranges that suit different applications, from Waxoyl type stuff to rubber compound sealers.

Regarding filling the sills, I think there is a bung about 1/2 half between the 2 wheels, although I haven't tried to take it out. Short of that you could drill a small hole and fill through there. Don't be tempted to weld it back up though...Waxoyl burns with vigor..

[notsofast]

Thanks alot Jos for your advice. My only worry about rubberised underseal is that if the seal is not perfect (around the edges) and moisture gets trapped under the rubber skin, then it'll be a recipe for even more rust!

The people who make waxoyl also make an underseal (with waxoyl added) which is prob not rubber based - I wonder if that's any good.

Cheers

[Jos]

I know the stuff you are talking about, it actually does seem ok but I would be wary of it, the only stuff that can take being hit with stones is the rubber based stuff. Trapped moisture I don't think would be a problem, most of the rubber sealers are either hygroscopic (asorb water during curing) or have agents in them that prevent the formation of rust. You could also treat any damaged parts with a rust inhibiting primer 1st.

The other option is to use Jenolite or a phosphoric acid based product, this converts the rust to Iron Phosphate and stops the rust apparently, I don't have a lot of faith in it though.. hydrochloric acid would be much more effective as it strips it down to the bare metal, but it also attacks the fresh metal making it important to neutalize it after it the surface is clean. You also need to paint it really fast as the metal oxidizes (rusts) almost immediately. Acid and alcohol mix prevents this to a degree (used in galvanizing)

When you are shopping about, have a look at Marine application stuff, it has to put up with a lot more abuse than cars do.

From what I have read if you have rust present on a metal, covering it up to prevent oxygen getting to it isn't actually enough to stop the spread. There is always a free oxygen molecule available as a byproduct of rust formation, this can go on to attack metal deeper down.

[Jesus325iTouring]

I was going to add my 2p's worth after doing reundersealing and waxoyling mine,but everything I've done has been covered nicely by Jos,my only tip is to warm the tin of waxoyl first in a sink of hot water,you get a much more even spread,oh and buy a mask for driving for the next couple of weeks after doing it,my car stank of waxoyl when I had finished

[Jos]

You can thin it down with petrol, fill the sills right up and let it sit for a couple of hours, then drain the excess back out again. It means you don't need to use loads and it cuts the weight down a fair bit.

[Jesus325iTouring]

You can thin it down with petrol, fill the sills right up and let it sit for a couple of hours, then drain the excess back out again. It means you don't need to use loads and it cuts the weight down a fair bit.

Thats a good idea,I might do mine again this year and try that way

[notsofast]

Thanks Jesus. But I luv the smell of waxoyl in the mornin'! Clears the sinuses.

Robert Duvall's immortal line in Apocalypse Now: "I love the smell of napalm in the morning. The smell, you know that gasoline smell, the whole hill. Smelled like... victory." Great movie and I betcha he sprayed napalm in the box sections of his choppers.

Which underseal did you use BTW?

Cheers