Thread: Rust on Z4's
View Single Post
      11-12-2012, 10:56 AM   #3
baege
Lieutenant Colonel
1321
Rep
1,589
Posts

Drives: 2022 Cayman GTS 4.0 6MT
Join Date: Jun 2009
Location: Toronto, Canada

iTrader: (0)

Quote:
Originally Posted by v3.2mc View Post
i found this... seems for BMW's 2006 and later there is a 12 year warranty against rust.
found this thread on e90 post which has me thinking:

The body of the e90 is dipped in a phosphate blend, this does NOT prevent rust. It does however clean the metals of contaminants and de-grease them. What this does is allows the base coat, paint, and primer to adhere to the metal much better which in turn is the rust prevention strategy.

The drivetrain including front and rear sub-frame DO NOT go through this process and are NOT painted. They are still highly susceptible to rust.

The BMW corrosion warranty is a PERFORATION warranty which covers ONLY THE BODY of the car. It does not include the subframes.

The 06 and 07 subframes are already starting to rust, especially around the carrier bolts.

Keep in mind that rust oxidation is caused by a chemical reaction between oxygen and the metal. Pure water does not cause much rust at all, however oxygen carried in the water will cause rust oxide. Salt will speed up the process via an electro-chemical reaction (electrolytes) very similar to how a battery works.

The undertray on our cars does not prevent all moisture from reaching our subframes unfortunately, nor do they help with humidity.

Rust proofing is very simple. It's a thick grease that the water (and oxygen) can't penetrate. If the oxygen can't get the metal, no rust.

It is not necessary to rustproof inside the doors, under the hood, trunk, etc. unless there is some type of damage that has penetrated the paints and to the metal. The hinges of doors, trunk, hood should be rust proofed for good measure. Rust proofing the subframe, especially the rear subframe is very important, especially the carrier bolts.

Washing the underbody after a salty drive will not prevent rust. You are now combining the oxygenated water with salt, making salt water and blasting it into crevices that potentially were not exposed to this previously. There are also undertray panels preventing you from spraying in a lot of areas where water from puddles and moisture in the air could penetrate. Including salt water, rain, snow from going in through the front kidney grills, ducts, around headlights, etc. and moisture getting onto the front subframe, bolts, etc. which can't be washed from the underneath.

It is not expensive to rust proof just the subframes. If you care about your car I wouldn't do it any other way. And if you have an early model e90 and you think rust proofing is a waste then ask a mechanic to put it on a hoist, take off the underpanels, and take a look yourself. You'll change your mind.
Appreciate 0