RTV Silicon warning
Thread Starter
Instructor
Joined: Sep 2021
Posts: 103
Likes: 29
From: Fort Worth, Tx.
RTV Silicon warning
that silicone (RTV) is potentially damaging to ferrous metals that can rust.An experiment at work went like this:
-We took a new bearing made in USA, (small sheilded type) and placed it in a jam/jelly sample sized glass jar.
-We then took about a half teaspoon of silicone rubber and smeared it inside the lid on the wax paper gasket.
-We then added 1 or 2 DROPS of clean tapwater to the jar and put the lid on tight.
-It sat and morphed for 3 days...after 3 days, the bearing was unrecognizable as a bearing...looked more like a turd.
When moisture is present, (we are in a humid environment in the south) the moisture seems to activate the curing RTV.
The curing silicone puts out corrosive fumes or gasses so strong that it attacks ferrous metals inside the area.
The brand seems to make no difference. We tried several brands of RTV and got the same results each time.
The blue, the clear, the red, etc...all the same.
We did NOT try the black sensor safe RTV...didn't have any at the time. Cant give a fair opinion on the black.
My son put RTV on the intake manifold bolts on a 440 buildup (the bolts screw into the heads in the vicinity of the
pushrods and rocker) to seal the oil from seeping around the bolts. 3 weeks later, the valve covers were removed.
Good thing he used oil on most of the surfaces. The pushrods and the rocker shafts were corroded noticably. We had
to disassemble and clean everything again. This time we used Permatex #2 for sealant. I dont recommend #1 Permatex,
as it gets hard and complicates future disassembly.
Drifting
Joined: Apr 2013
Posts: 1,748
Likes: 268
From: Central Wisconsin
Funny you should mention that. Few years ago I had an idea. To cover my bleeder screws on my brakes with silicone to keep them nice and shiny when I needed them. Looked pretty bad when I removed the silicone a while later.
Safety Car
Joined: Nov 2002
Posts: 4,181
Likes: 1,177
From: out of nowhere
I’ve been wondering lately… What about liberal application of anti-seize on bolts where oil/water might migrate through threads? If that works to prevent the migration, wouldn’t that be the best of both worlds? Anti corrosion/anti-seizing and no oil or water weeping from said bolts? What says the experts?
Advanced
Joined: Nov 2023
Posts: 89
Likes: 59
Most RTV releases acetic acid as it cures. That would be the primary source of rusting. The "sensor safe" RTV has either zero or very minimal amount of acetic acid, depending on source. In situations where oil or water might migrate past threads, blue loctite is a good solution. It doesn't make removal difficult, but it does seal the threaded connection and isn't messy like anti sieze compounds.
Tech Contributor
Joined: Aug 1999
Posts: 15,160
Likes: 3,965
From: Connecticut, USA
Back when I was a Facilities Manager and taking care of a 65k sq ft building with metal roof we used urethane caulk for sealing the joints as opposed to using silicone for the very reason that the silicone was acidic and would attack the metal panels.
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