BMW Exhaust Heat Shield Repair

Some repairs will require removal of the complete exhaust system, in my case, removing the engine for turbo replacement, and replacing the left rear drive axles. With the exhaust removed, you have access to all the heat shields, and the driveshaft tunnel heat shield needs to be removed in order to inspect the driveshaft and the front driveshaft flex disc. 

In my case, I had some pretty serious galvanic corrosion of certain heat shield connections, particularly at the driveshaft tunnel brace, and a couple mounting holes for other various heat shields. This is a Canadian car, and it's used summer and winter, exposed to a lot of road salt and spray. I checked into replacement OEM parts from the dealer, but they are pretty expensive (probably due to the shipping cost of large, lightweight parts). 

I did a quick repair, which consisted of cutting a square of architectural aluminum, 23 gauge (0.57mm / 0.023") thick, larger than the hole to be repaired.

E60/E61 Muffler Heat Shield. 

I would contour the patch to the shape of the heat shield. It doesn't need to be exact, because the aluminum is pliable, and it will take the final shape required when replaced in the car. 

Patch riveted onto Muffler heat shield.

Inside view, note the gray spray paint which is cold galvanizing compound.

Once the patches are complete, I'll spray all the general area of all the fasteners, front and back sides, with a thick coating of cold galvanizing compound. The galvanizing compound contains zinc, which is sacrificial to aluminum on the galvanic scale, meaning that theoretically the zinc should oxidize before the aluminum when put back in service, protecting the aluminum from corrosion. 

Heat shield replaced on the car with a new body nut.

In one case, I installed the body nut reversed because the weld screw had broken off and was shorter than usual. 
Galvanic corrosion around the driveshaft tunnel brace

What's interesting about the galvanic scale and the corrosion of the aluminum heat shields, is that the heat shield corrosion is probably protecting the steel chassis and body of the car from some corrosion. 
Patch on the driveshaft heat shield, in the area of the driveshaft tunnel brace. 

Driveshaft tunnel brace was so badly corroded I simply replaced it with a new OEM part

Driveshaft tunnel brace - bottom side

The heat shield repairs that I did 2 years ago and just recently inspected have been holding up will, with no further issues. 

One maintenance habit I'll make now that I'm committed to keeping the car until it runs into the ground will be to try to remove the underbody protection (not necessarily all the heat shields) and get underneath the car to spray off all the salt following the winter driving season. The amount of salt and road sand that the underbody protection can capture is impressive. 

I'll do a separate post on the corrosion repairs I've done on the body, and the rear bumper. More to follow. 


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