Using silicone sealant as exhaust paste

[aww999]

I've never tried it, but have heard from a few different sources that ordinary bathroom silicon sealant can hold up to the high temps of exhaust components. I have a small aluminium plate I need to fix to the back of my cylinder head, which will blank off a feed from the exhaust port of #6 cylinder to the EGR equipment (which has been binned!). I have no exhaust paste. I have silicon sealant. Access to the spot is limited but possible at the moment, but once the exhaust manifold, turbo and wastegate plumbing are added it will be a nightmare to get to so I would prefer to do it correctly and do it once. Anyone have any experience of using silicone in this way?

I have an exhaust gas temperature probe in this runner, and temps run around 850C.

[steve bowen]

It'll kill your O2 sensor as its in front of it. In my experience silicons is far superior than exhaust paste at making good durable joins between exhaust flanges (past the O2 sensor). Hayward & scott use and recommend it if you don't have gaskets.

[Moose.]

It'll smoke like mad the first time you get it hot, but after that it works excellent. Much better than normal exhaust paste as it remains flexible. I found exhaust paste would go brittle and eventually the join would leak with the vibration.

As mentioned though, don't use it before the O2 sensor.

[redgriff500]

It may work Ok at the back...

But on my tube it says only good to 250 degrees, I believe you can get high temp stuff but I think it only goes to 500.

Edit - found this on the first site I looked at:
Silicone adhesives and silicone sealants are based on tough silicone elastomeric technology. Silicone adhesives have a high degree of flexibility and very high temperature resistance, up to 600 degrees F,(315C) when compared to other adhesives

Edited by redgriff500 on Friday 2nd March 14:50

[gafferjim]

Used it to join up a 4-1 motorbike exhaust as there were no physical "clamps2 as the other posters state, it will smoke & smell the first time, but b y gum it works, when I wanted to separate them some years after, it was near impossible

[oogieboogie]

hmm... I used clear gasket repair on my bathroom once - worked just fine !

[EDLT]

I'd weld the plate on.

[r1ot]

Don't use exhause paste before your catalytic converter either as you will knacker it

[aww999]

Thanks guys, sounds like it will work fine. I can run without an O2 sensor until the silicone has heat cycled a few times, I will probably only need to use about 10 grams of it at most as the port I need to block is tiny.

[anonymous-user]

I use it to seal the manifold to the head on race cars. The secret is to make sure the surfaces you are mating are completely flat when clamped down, otherwise the exhaust gasses will burn their way past the silicone and the seal will start blowing.