Firewall corrosion

[Dward]

Hi folks,
I am hoping someone can lend a little advice. As you can see in the picture below I have some acid corrosion on my firewall around, and mainly, below my battery box. I thought I was doing well by putting a float charger on my battery over winter but it caused my battery to vent onto the firewall. As you can see the worst appears to have run down behind the gascolator bracket.

My plan is to remove the battery box and gascolator. Then clean with red scotch brite and WD40 or corrosion X. Does this sound ok? Also, what should I cover it with now that the cladding is gone? I was thinking either zinc chromate or cold galvanize. Any help would be appreciated.

[GAHorn]

It sounds as if your plan to clean it up and treat it with zinc of some sort is a good idea. I like aerosol galvanize on other steel items. I'd imagine it'd do well in this application as well.

[n2582d]

Dave,
Last year I was able to help another member out by giving him a section of my old firewall to patch his firewall that had corroded in a similar manner. Your's doesn't look like it is so far gone as to need skin replacement though. I'd make sure you check and take care of any corrosion between the bottom skin and the firewall attach angle as well as below the rudder bar area. Corrosion X is probably a good idea after you get it all cleaned up. It's interesting that the battery drain tube is not doing its job. I'm guessing that the drain location is too far forward and battery acid is pooling aft of the drain hole.

As a side note, could you tell us about your oil cooler? Is it one from Steve's Aircraft?

[GAHorn]

I have found many battery box drain tubes (aluminum) to be so full of corrosion as to be blocked. I've also found them plugged with insect nests.
It's a good idea to wash the box out regularly with a water hose, and maybe even a little baking-soda solution, followed up of course with a shot of WD-40.

[blueldr]

What did you use as a "Float Charger"? A real float charger will not charge a battery beyond "Full" and cause it to "Boil" over.

[hilltop170]

Before you put any oily liquids on the firewall which could later affect the cold galvanized spray adhesion, wash the firewall down with lots of soap and running water while scrubbing it down with a stiff non-metalic brush to get rid of residual acid that may be lurking in seams, etc. ScotchBrite will remove existing remaining galvanized coating so I would not use it.

You can then add a box of baking soda to a bucket of warm water and brush it into all areas which could have been exposed to the acid to neutralize any remaining acid. Then wash it off with lots more soap and water.

Dry thoroughly before treating with cold galv spray (available from Home Depot in spray cans, which is what I would recommend since the firewall is galvanized steel). Only after the galv is fully cured would I then spray with Corrosion X.

[Bruce Fenstermacher]

I'd do Richard's process but would not coat with Corrosion X. I don't think there is much to gain by coating the cold galvanizing with CorX. The cold galvanizing should seal any seams or overlap so the CorX can't even get there.

Treating or stopping the corrosion and neutralizing the acid before the galvanizing is the key.

The problem with a float charger is that unless it was designed specifically for an aircraft battery, it is not likely to work correctly as evidenced by the boil over. Aircraft lead acid batteries are not the same as car and motorcycle lead acid batteries. The electrolyte is heavier.

[blueldr]

Bruce,

I have activated a number of standard lead acid aircraft batteries and have always used the standard specific gravity electrolite.
Which type of lead acid battery uses something different and what is the specific gravity ?

[GAHorn]

I think cold-galvanizing doesn't need WD40/Corrosion-X...in fact it probably works best if exposed directly to air. (Zinc is sacrificial but not if insulated with preventative. My previous suggestion was purely for that drain tube, not the firewall.)

Dick, I believe Bruce is technically correct in that aircraft batteries come with electrolyte which claims different S.G. than automotive type batteries, ....although doubtless the batteries will still do their job pretty well with whichever is used.

From the Gill website:

Can I use automotive electrolyte in my battery?

No……not recommended! Automotive electrolyte is only 1.260 Specific Gravity. By using automotive electrolyte the battery will not function to it’s intended capacity because the cell electrolyte balance would not be up to the required levels. Gill electrolyte is 1.285 Specific Gravity. Warranty will be void if the proper specific gravity electrolyte is not used.

Here's a list of FAQ's Gill produces http://www.gillbatteries.com/faqs.aspx (note they do not recommend charging in-situ on the ground, nor beyond/less-than 1/2 amp from an automotive (typically constant voltage) charger. As bluEldr points out...REAL float chargers usually do NOT actually charge a dis-charged battery...they only supply a pulsed currect to delay the onset of sulfation. Harbor Fright is not the place to buy your "float" charger. By the time you spend the money to own a REAL float charger....you could afford to replace your battery every 3 years, as recommended by flooded-cell mfr's.

Also, AGM/Gell-Cell/DryCell/etc batteries do not like float chargers. Just like your engine...aircraft batteries like to be used on a regular cycle-basis. Avoid deep-discharges and avoid long periods of inactivity. (It's better to reverse Ol'Gar and bluEldrs techniques.... between long periods of aviation inactivity...to get maximum use out of your flooded-cell battery, use your aircraft battery in your LAWN TRACTOR....not the reverse.)

[Dward]

Hey Guys,
Thanks for the great advice. Sorry it took so long to get back but I wanted to snap some pictures on the way to work this morning. I’m going to clean the firewall thoroughly with baking soda and a bristle brush then paint with galvanize spray paint. I’m still not sure what to do at the bottom where the belly skin overlaps the firewall attach angle. It looks like some run off pooled there before it dripped off.

The drain tube is open but the acid gas vented to the rear and up so it hit the firewall above the battery box. Remember the lid was off with the float charger hooked up. You can see some white residue where I used baking soda on this area.

Gary, here is a better picture of my oil cooler. This is a 337 installation not an STC. It uses the holes in the rear baffle where the generator blast tubes used to hook up for the cool air supply. I lost my AC logs in a house fire a couple of years ago but I ordered the CD from the FAA and it contained the documentation for the cooler installation if you are interested.

BL, here is the source of my pain. Thinking back on it I believe I may have dropped this little jewel at one time. Maybe I scrambled it’s little brain. I think from now on I’ll just fly to maintain my battery.

Thanks again everyone. I will update when progress is made.

[bagarre]

I've found that a bad oil filter gasket provides ample firewall corrosion proofing
Sorry, I couldn't resist.

[GAHorn]

...Gary, here is a better picture of my oil cooler. This is a 337 installation not an STC. It uses the holes in the rear baffle where the generator blast tubes used to hook up for the cool air supply. ....

An STC also requires a Form 337 for the records.

What are you using to cool your generator? (or did you convert to a fanned alternator that req'd no cooling air supply?)

[hilltop170]

After everything is cleaned, firewall re-painted with Cold Galv spray, and back together, if the battery box is left bare aluminum anywhere, a good coat of CorrosionX will prevent future corrosion as long as you re-coat every year at annual when the battery is removed for servicing. Also, coat the battery terminals after they are tightened and they will not corrode either. CorrosionX is amazing stuff.

I agree, CorrosionX is not required on the firewall, but if there are bare spots in other places on the firewall where Cold Galv spray can't be applied, CorrosionX will keep those areas corrosion free with a once per year application.

Then, I would definitely liberally apply CorrosionX to any seams or lap joints that were exposed to the acid run-off bacause it is unlikely that you would be able to remove all traces of acid that wicked into those areas and which would re-activate any time moisture is present.

CorrosionX gets between the corrosion cells (metal parts) and electrolyte (acid and moisture) and breaks the electric circuit which prevents corrosion. It really works.

[Dward]

Thanks Richard, I may go ahead and paint the inside of the battery box with acid proof paint when I have it cleaned up. For some reason the lid has this treatment but the box does not.

I’m thinking I will use my spray gun to blast some baking soda mixture into the belly skin joint followed by corrosion X and then keep an eye on it. If I see any white powder form in the joint I can drill rivets at the next annual.

George, I should have said “field approval” not 337 I think. I forgot they are not the same thing. Also you are correct in your guess that I have a fan cooled alternator. The oil cooler supply hoses have close outs on the rear baffle wall that can be closed in cool weather to allow a higher oil temp.

David, my old engine kept the tail wheel lubricated

Thank you all again.

[GAHorn]

Dave, I'm not sure it's a good idea to force soda-solution into an area unless you're confident you can also wash it back out with clear water. Acid can corrode...and so can alkalie/base materials including soda. (I.E., don't leave soda in there expecting white powder to prove witness to on-going corrosion.)

I'd flood the area of the lap joints with baking soda solution...let it dry overnight...then wash it thoroughly with plain water, and then let it dry and then treat it/flood it with corrosion inhibiting WD 40 or something more expensive you really feel needful.