Removing old sealant


#1

the fuel tank hose cover of the late MY Porsche 944 is attached using nuts/studs but also a thick line of black sealant, which my best intuitions tell me is silicone, like the “Ultra Black” in the FLAPS. When the cover is removed, black sealant sticks to both the painted sheet metal of the interior of the car, and also the black metal cover. Would like to hear some ideas how to remove it. My current plan is to just leave it alone and add fresh during reassembly.

Here’s what I have tried to remove the sealant - which is partially melted from fuel vapor : a plastic scraper, blue paper towel, plastic brushes and Goof-Off. I have tried pouring a deep (~1/2 inch) volume of Goof-Off in a waste pan and dunking small portions of the cover and scrubbing it, with some progress. Apparently, no paint comes off this way. However, Goof-Off removes paint from the mating surface for the cover that is on the car. Both the cover and the car have unusual surfaces, so a brush becomes necessary. BTW there is a “packing cord” which is also listed in the parts diagram, however I did not obtain this, and it appears from removal to be a thin thread, which I do not understand how to use anyways.


#2

Solvents don’t usually work very well on silicone sealants. Goof off is a very mild solvent. I usually take silicone off with a razor blade or scotchbrite pads. The pads are best for non-flat surfaces. If the stuff transfers to your fingers, it is not silicone and will usually come off with acetone or lacquer thinner. Good Luck, cleaning off old goo is a constant task with restorations!


#3

@Mustangman you read my mind - the old sealant easily sticks to everything and stays there. I thought Goof-Off was strong - oh well. It sounds like the paint is going to come off with the sealant.


#4

I think its possible that you have polyurethane sealant, not silicone. the kind used on windshields.

it is much, much stronger than silicone, which I ve found easily comes off painted surfaces, and bare metal too. the urethane is really hard to remove from anything . a sharp hard plastic ice scraper may work, to an extent. if it is polyurethane, it will adhere well to itself if you use it when replacing cover


#5

@wesw that makes sense - I will try to post back my results.


#6

Brake cleaner may work, but I don’ t know if it would damage paint.


#7

quick update on this:

browsed through Lowe’s the other day, saw the 3M Marine Sealant 5*** (can’t recall number), definitely a polyurethane sealant. an MSDS from 3m on one of their Marine Sealants (5200) contains heptane (among other things).


#8

I don’t know what it is but instead of lowes go to an auto store like NAPA that sell body shop supplies and ask. Go to lowes if you need a 2x4.


#9

It’s chemistry. The 3M product, whether found in NAPA or Burger King, tells you that polyurethane is dissolved in heptane.


#10

lowes has a good selection of sealants and are much cheaper than the auto parts stores for polyurethane. when I did a back window in a cougar, I think lowes was 8-9 dollars compared to 20-22 dollars at napa for the same thing


#11

in fact I buy many things at lowes. much better quality stuff than wal mart. good prices too. plants, lawn equipment, firepits, fasteners. nice wood too.