When I first purchased my B200 in Dec. 2005 I noticed what I thought might be a future problem under the bonnet .
Because MB has dumbed it down and not included a bonnet insulator, we now have a problem.
When driving in the rain or salt spray as we often have in the winter months here in Canada, this spray hits the interior of the bonnet and tracks to the interior sides and front lips.
The sides of the bonnet have great drainage slots, but the front has 3 points without any drain holes.
If you close the bonnet and look at the 2 lowest points of the bonnet near the head lights, these low points can and have trapped water in mine. Opening the bonnet drains the water out mostly, but moisture is still trapped.
I showed this to my stealer and their response was, yes it is a problem but what can we do!!
I drilled small drain holes in 7 locations under the bonnet and my problem is solved.
If I receive interest in this posting, I will gladly give a more complete procedure if requested, as this is a delicate procedure but very doable. Hopefully MB will correct the stamping holes at the build time and eliminate my repair for future owners.
"REVISED"----From 2008 the drain holes are now there!!!
Last edited by Derek Lecours : 11-03-2007 at 07:16 AM.
Hi Paul, With our Canadian winters it's sure to rust, the only question is how long it takes to rust out.
The metal surfaces are close together but not touching therefore without proper drainage, as is the case, all "B" class will be affected until they change the stamping at the factory, before the 2 hood pieces (bonnet) are pressed together.
The paint is good so the rust won't happen overnight, but it will make for a lot of unhappy "B" owners in the future.
My dealer was amazed when I showed him the hood. I can't imagine how this defect wasn't spotted during the designing stage.
In the near future I plan to install my own bonnet insulator and this will reduce the chance of water getting in. Time will tell !
Last edited by Derek Lecours : 11-03-2007 at 07:16 AM.
I think an insulator is installed to prevent excessive heat from reaching the exterior painted surface of the hood.
It also reduces sound from entering the passenger compartment and reduces splashups from tracking inside the hood.
Heat should dissipate quite well due to the fact that the motor compartment is open to the ground in many areas when looking down .
The holes are there for the insulator, why didn't they include one ? Derek
Last edited by Derek Lecours : 11-02-2007 at 10:54 AM.
. The holes are there for the insulator, why didn't they include one ?
Another cost cutting exercise probably.
Regarding the bonnet drainage would it not be possible to fill the offending part with something like Waxoyl (a liquid semi hardening wax) as by drilling into the bonnet you are actually baring the metal which in turn could lead to rusting.
I understand your concern & your resolution to the problem but how would M/B respond ( under the anti corrosion warranty) to a bonnet that had been drilled & subsequently had rusted, would they blame the drilling for the rust problem ?
The best solution is proper drainage.
I've done this by drilling a few small holes. There are a lot of little details I didn't include in the first posting.
Where the drill bit penetrates the first sheet of metal, primer and painting with a little brush is recommended followed by proper drying and hardening.
Your wax idea is good. The cavity protection spray I used is sold at the MB dealer (Part # A 000 986 33 70 10 ). It comes with a long nozzle which I tracked deep into those same holes and liberally sprayed every place I could find on that hood (bonnet).
Another product is by the Wurth company also of Germany, Part # 0893.081-A and is also a cavity wax used on Audis.
Our 'B' has a great application of cavity wax from the factory, but is mostly applied to the underbody, but we can always improve on it.
I've also done a lot of touch ups by brush with the same products purchased in a non spray form. Filling the trapped area with wax might work, but I won't chance it.
We live north of Montreal, and we live with 6 months of salt spray on our highways. I figure 1 salt season is equivalent to 10 rainy seasons elsewhere and I'm not too worried about the MB rust warranty because I don't know anyone whose ever collected, do you?
If anyone attempts to drill, you must stop the drill bit from touching the 2nd sheet of metal by sliding a mylar strip of insulation down into the offending cavity before you attempt to make this hole, you then remove the mylar strip after the hole is completed.
You could also use a step drill bit to block deep penetration, and you should also use a center punch mark to guide your drill bit.
There is no room for error when doing this drilling. I hope to get pics up for you soon. Derek
Last edited by Derek Lecours : 11-02-2007 at 10:56 AM.
Rust Problem For All B200 Bonnets (Revised) 
Linear Mode
