Where to apply seam sealer in engine bay?

[Bmachine]

I've read several post where people mention applying seam sealer prior to painting. I wanted to double check the critical locations where this should be done in the engine bay area.

So far I am thinking:
- Where the upper part of the firewall is welded to the fender and the heater fan area. (First 3 pics)
- All along the flat horizontal area where the fender lip goes over the inner fender. (Fourth pic)
- In the two far left and right corners flat area near the A pillars. There is a scary looking cavity there which looks to be a perfect water trap. I have seen a piece of rubber that seems to make a fairly weak barrier to keep water from entering that area but I would think water can sneak in there from either side of that rubber. The tricky part would be to be able to push the seam sealer deep enough since it is only about a centimeter or so high but more like 4 or 5 cm deep. (Last pic.)

Does that make sense?

Here is what I am talking about:

 

[Gransin]

Bo,

I used a product called Sikaflex 252 as seamsealer everywhere on my car. I don't know if that product is easy to get in the States, but I'm sure there are many different options.
First I put a layer of epoxi paint all over my bare shell, when that had dried for a while I put on the seamsealer, and on top of that came the other layers of paint. But you can put the seamsealer (at least Sika 252) straight on to the metal just as good, if you wont be using any epoxi.

Make sure you use a seamsealer that's paintable, otherwise there will be lots of tears..

About the corners near the A-pillars, I didn't put anything there. My thinking is that it's better that it is ventilated than totally sealed up. But I sure did have the rustproofing guys at the shop spray a lot of oil (or whatever product they're using) everywhere in that cavity after the car was painted.

Another thing that came to mind, the seamsealer was applied with a brush from factory, but that was very hard to replicate at least with the Sikaflex 252, if you have the possibility and want to have that brushed look no matter what product you end up using, do some experiments before and try to find a good way to get it looking nice, and not like me with a very tight time limit and without a store close by to buy and try different brushes.

Can't comment on where they actually had seamsealer from the factory, but I'm sure someone else can chime in, I put it almost everywhere

 

[eriknetherlands]

Bo,
I can't help you with factory specs on where seam seal was applied. My car was repaired in the front, so not original anymore in that area.

I would keep the area of the last picture open. Think about seam sealing as being SEAM sealing; where two plates are in contact water will be sucked into it (capilair action) and will have a hard time evaporating, giving it time to eat your metal. That is where seamseal is a solution; covering the seam from both sides. Also don't forget that every seam also has a front and back end to it; close these seam ends as well. Big lumps also tend to shrink a bit over time, and then it is creating even more crevisses.

Should you manage to dig up some reference pics or specifications, do post (or link) them here. I'm sure others are intersted.
Erik

 

[Bmachine]

Thank you Robert and Erik. Yes, that A pillar area is best left alone. That is a really strange design/engineering decision btw. Why create an obvious rust magnet pocket such as that one???
There was a piece of rubber that was supposed to keep most water out of that area in my car. But it was very dried up and in poor condition. I need to get more of that. I'm sure if I do a search there will be someone who has found a good replacement part.

 

[Gransin]

Thank you Robert and Erik. Yes, that A pillar area is best left alone. That is a really strange design/engineering decision btw. Why create an obvious rust magnet pocket such as that one???
There was a piece of rubber that was supposed to keep most water out of that area in my car. But it was very dried up and in poor condition. I need to get more of that. I'm sure if I do a search there will be someone who has found a good replacement part.

Bo,

Those rubbers can be a little bit tricky to figure out from the parts diagrams.

They are part#: 51711810529, you need two pieces. Don't know if they are available from BMW, but W&N has them in stock (a little expensive, 35€/each).
Number 11 on the diagram, don't know why they made the diagram that bad.

 

[Bmachine]

Excellent info. Thank you Robert.

But 35 euros each for a couple of 20cm rubber pieces???

 

[Paul Baker]

I've read several post where people mention applying seam sealer prior to painting. I wanted to double check the critical locations where this should be done in the engine bay area.

So far I am thinking:
- Where the upper part of the firewall is welded to the fender and the heater fan area. (First 3 pics)
- All along the flat horizontal area where the fender lip goes over the inner fender. (Fourth pic)
- In the two far left and right corners flat area near the A pillars. There is a scary looking cavity there which looks to be a perfect water trap. I have seen a piece of rubber that seems to make a fairly weak barrier to keep water from entering that area but I would think water can sneak in there from either side of that rubber. The tricky part would be to be able to push the seam sealer deep enough since it is only about a centimeter or so high but more like 4 or 5 cm deep. (Last pic.)

Does that make sense?

Here is what I am talking about:

We always replicate a BMW UK owned CSL that I saw at a show, I was told that it was as untouched as I would find. To be honest the sealer was very messy but it did look like it was factory so we copy that. A few other cars have looked very similar albeit rusty.