Undercarriage rust prevention...1987 Carrera

[Dueller]

I have a rust free 1987 Carrera. It has always been a southern car and never near salt. I want to keep it that way. In doing a thorough cleaning I have pressure wash undercarriage and Fender Wells. There is no rust but the light coating of I assume Factory undercoating is beginning to come off. What do you recommend to coat it with? Fresh light coat of undercoating, strip old undercoating and reapply, p o r 15?

[Dueller]

Here's an example of what I'm talking about. Front fender well. The brownish black color you see is the old undercoating.

[Ctopher]

That looks just like dirt, grim and oil residue. I would suggest taking the wheel off and clean with a degreaser and a soft brush.

Here are some pics of my 87, California car that had a full detail.

[sugarwood]

Those look like snow tires.
Maybe the first step is to mothball it for half the year like most owners. ;-)

[Dueller]

Originally Posted by sugarwood

Those look like snow tires.
Maybe the first step is to mothball it for half the year like most owners. ;-)

LOL...not much snow in deep south Mississippi. But plenty of rural dirt and gravel. A/T tires....

[Dueller]

Originally Posted by Ctopher

That looks just like dirt, grim and oil residue. I would suggest taking the wheel off and clean with a degreaser and a soft brush.

Here are some pics of my 87, California car that had a full detail.

WOW....That is clean. Any idea what was used to clean with?

[jjeffries]

Please.....banish all thoughts of POR15. It has legitimate but limited applications but your (off-road?) 911 isn't one of them. Maybe that rusty swingset in the neighbor's yard? It would be good for that, but not your beautiful German automobile.
I imagine the most significant ingredient in getting your wheel wells to match the other beauties posted is elbow grease, along with something citrus-based, although if what's coming off is dealer- or PO-applied tar-based underseal spray, some mineral spirits in a mist bottle would help dissolve it.
That factory coating is almost like sprayed-on caulk, and surprisingly durable. If it gets cracked or otherwise violated, you can feather it back with a stiff wire brush cup on a grinder and spot apply a high quality analog from 3M; UPOL and Wurth also make good products, some in convenient aerosol cans. It needs to be paintable.
One thing I tell anyone who's doing anything on their Porsche or other fine car that involves paint or coatings: go to a commercial autobody paint/supply distributor and ask them what to use, and buy it from them. The stuff sold in chain car parts stores generally sucks. Of course, take proper care with safety gear to apply it.
The other place where rust can blight an otherwise good looking car's underside: the fasteners, especially when plating fails. Replating is the best way. If you can't swing that, wire brush the rusty fastener then use something cosmoline-like to coat the hardware,; a quick spray of 3M Cavity Wax will do the trick. Best of luck, John in CT.

[tdw28210]

Yeah no POR 15. It is really a rust converter. Unless you plan to introduce rust to the car, it is far from the best stuff to use. And as others have already posted - clean the underside first and then do an assessment.

[Ctopher]

Originally Posted by Dueller

WOW....That is clean. Any idea what was used to clean with?

An APC, different brushes and lots of elbow grease. It’s a bit of work but once it’s cleaned it’s easy to keep it that way. Basically I would follow similar directions on engine bay cleaning but with an APC. I prefer to use Simplegreen Aircraft which is safe for aluminum. Actually I’ve used it in a foam cannon before and am planning this method for further engine bay degreasing.



If you want to go the easy way but more costly $$ consider having the car dry ice blasted. It’s similar to sandblasting but used dry ice as media. Do some searches, amazing what it cleans with little work. And it’s safe on metal, plastic, rubber and from what I hear cleans away just about everything from dirt, grease, oil, etc.


Ctopher

[jlex]

Ever hear of Fluid Film? May want to give it a light coating of FF after cleaning. A DIY'er can apply it using aerosol cans without making too much of a mess.

[Dueller]

Thank you all for guidance. Aside from dry ice blast any other suggestions for removing stubborn patches of undercoat? Judicious use of heat gun require getting it almost hot enough to bubble paint before undercoat turns loose.

[jjeffries]

Eeek! I wouldn't use a heat gun.
As I see it:
The facory underseal is GOOD...and you don't want to bugger it up.
Heat gun will cook it, separate it from the metal and make it crispy, flaky and worst, will break it's adhesive bond from the metal below. Then? Water gets in and all hell breaks loose.
Your mission is one of scrubbing.

[Ctopher]

Originally Posted by Dueller

Thank you all for guidance. Aside from dry ice blast any other suggestions for removing stubborn patches of undercoat? Judicious use of heat gun require getting it almost hot enough to bubble paint before undercoat turns loose.

Let’s be clear on what you are asking. You showed us a pic of your wheel well, at least from the factory that I know did not include undercoat. What I suggested was both meant to help clean the dirt, grim, oil, rubber, etc. that accumulates over the years in the wheel well. Is that all you are looking to clean, just the wheel wells?

If you are referring to the grayish undercoating actually under the car....ie floor pans... then I suggest you leave them alone. Unless it’s already coming off then repair it as others have suggested. I would not recommend removing all of it especially if you intending to drive the car off road with your truck tires.

This is my recommendation and I’m sure others will comment with similar suggestions.


Ctopher

[Dueller]

Ctopher....to clear it up a bit. I've owned the car for over 20 years. Over that time it was a DD for about 8 and then weekend toy/track car. The relatively thin undercoating has over time begun to lose its grip and with flaking off makes the car fenderwell/underbody look like it has leprosy. So I'm looking for inpUT of which way to go...strip the remaining undercoating, undercoat again, respray undercarriage...what product, etc.

Thanks in advance for suggestions.

[Dueller]

A little addendum about the all terrain tires. Boys being boys I made performance mods over the year to suit Track & D E use. However about 5 years ago I suffered a stroke that partially paralyzed my left side and made it almost impossible for me to get in and out of the car with it lowered. Additionally, my health condition was not safe for me to be participating with other drivers on the track. I had always admired the Paris Dakar Rally cars, and decided to lift my car to fit me. I started this project long before the current Safari fad. Granted I could have sold it and made good money considering I purchased it at the bottom of the depreciation curve and before the latest crazy values on these cars, but I enjoy the car so much that I'm going to figure out how to continue to enjoy it in my own way. Hope you guys won't chastise me for doing this to a classic.

[Jesse16]

I have a red (had till I painted it blue) 87 also and mine has always been a southern car, Georgia/Jacksonville FL car. Like someone said up above I would leave what you have alone and just keep the car dry in general and rust should not really happen. Mine has never looked better than your before photos above. I've been my cars keeper for nearly 10 years and even though it sees rain several times a year during long drives of one sort or other its still rust free, count on the galvanize to help a lot. I think most everyone here loves it when owners do their own thing to keep enjoying the cars. Next person can do with it as they wish.

[Dueller]

Thanks, for adding that last comment, Jesse.

Mine is an original paint car, but I enjoy the patina and stone chips probably more than if I did a perfect respray.

[FrenchToast]

I would start with, if possible, posting more pictures of the peeling undercoat about which you are concerned.

I am going to echo others and say that, unless it is peeling or there is visible rust behind it, leave the factory undercoat alone. It was applied in ideal circumstances (relatively sterile, low humidity, etc.). If you feel it is thin and could benefit from a thicker coat, you could apply some more on top.

If you want to replace some sections of undercoating, Wurth and other companies that cater to professionals generally have a good product. If you have a local bodyshop you might be able to make friends and borrow their undercoat sprayer, or you can source one. Some products you can also brush it on. Generally the factory would prime the metal (after galvanization), then undercoat, then paint. Degrease the area first for optimal adhesion (not sure if sanding is required for undercoat - check product). Remember to wear proper eye, nose and mouth protection. Many products are particularly toxic.

Galvanized metal alone is better than the alternative, but unlike Porsche's 1977 publicity stunt (leaving a bare galvanized shell outside for ~6 years without any signs of rust), it is not invincible. The only reason the stunt worked is because the car had no seals and was never driven. The drains never clogged, and no dirt or moisture built up in crevices and under seals.

[CrankyBurroMXer]

I believe Porsche did build a few Stainless steel shells in the 60's and drove them around the continent a couple hundred thou klicks. I saw one on display in the Deutsches museum a long
time ago. Would have made a great option. https://goo.gl/images/nCBq2F

[Dpmulvan]

factory undercoating doesn't just flake and fall off.