Beware the perils of silicone sealants

Vic.S · Jun 20, 2010

I thought I would share the picture below with you.

An internet forum acquaintance is working on a 1982 4hp and has taken the power head off to investigate lack of cooling water flow.
He found that it had obviously been off before and reftted using the old gasket and lashings of silicone sealant.
Water-way to the power head completely blocked with silicone!

bktheking · Jun 20, 2010

Re: Beware the perils of silicone sealants

That`s called servicing the `wrong way` , i`ve seen people use silicon to replace the water tube grommet on the 9.9`s, its called being cheap. Cheap and outboard don`t go together.

mla2ofus · Jun 20, 2010

Re: Beware the perils of silicone sealants

Some ignorant people think if a little silicone works good then a bunch should do even better. There's no evil in silicone unless it's in the hands of stupid people.
Mike

wilde1j · Jun 20, 2010

Re: Beware the perils of silicone sealants

Silicone sealants have almost no place on any outboard.

LongLine · Jun 20, 2010

Re: Beware the perils of silicone sealants

I work for a gasket mfg. We always recomend going with the thinnest material required. i.e. don't use 1/8" thick if 1/32" will do. Guess that photo is proof that no gasket material should be put on so heavy.

Tom B.
(LongLine)

jmendoza · Jun 21, 2010

Re: Beware the perils of silicone sealants

How true about silicon sealant, and guess what? It's not oil or gasoline proof either, so don not use it to seal anything where petroleum products are in contact with it. It will seal in the short term, but once exposed to petro-chemicals it will soften and go away, causing a leak. Orange, blue, clear, or black silicon sealant on a gasket or sealing surface is the mark of a shade tree mechanic for sure, if you see that, assume everything needs a good once over! Use silicon for window and bathroom caulking, as that's what it's designed for. Why Permatex markets this stuff as engine form-a gasket is beyond me, it's not suitable.

We do use it on our Go Kart McCulloch engines, but we tear them down and re-seal them after every race, so it will hold up for a short time. The reason we use it is because it's easier to clean off and remove the gaskets. But for permanent assembly with a long service life, and no expected tear downs, then Yamabond, Three Bond, or better yet the OMC anerobic sealer (metal to metal surfaces) is the best.

McGR · Jun 21, 2010

Re: Beware the perils of silicone sealants

Every sealer has its advantages and disadvantages. There's no one size fits all. In the right place, silicone sealers work great. Generally, they aren't the first choice for most outboard applications. However, they have been widely and successfully used in may OEM automotive applications (including those exposed to oil - i.e. valve covers, differential covers etc.) for many years.

Fuzzytbay · Jun 21, 2010

Re: Beware the perils of silicone sealants

I've used silicon sealents for years, on many things from my JD' 510 rocker and oil pan covers, to water pump housings, carb gaskets, on my older outboards. There is of course a proper manner to use silicon ( and proper silicon for each type of application). It is not designed to be put on, then install and torque down the mated part. That is the most common problem, and it appears to be what happened to parts shown in the picture. Besides being the wrong type of silicon as well. Instead you apply the product, lightly seat the other mated half, let cure, then bolt up, as a general rule.
In general its best to use OEM products, after all that is how they were designed and built. Yet to paint silicon as something to be avoided, that too is not the best advice.

Tim Frank · Jun 21, 2010

Re: Beware the perils of silicone sealants

Since the thread has gone this way....sealants....I don't think this is a hijack....
I am going to be R&R a lower unit on a 6 hp. E/rude ...1975.
The purpose is to reseal as there is some water infiltration not due to the drain plugs.
There is a ~ 12" piece of round-section gasket that is the seal between the lower gearcase casting and the upper...and sits in a groove that is in each 1/2.
I understand that this should be "helped' with an application of asealant....the local dealer said you have to use "this" and offered me a $9- can of an OMC specialty product that would seal 100 gear cases....

There is NO rush on this as i had to order parts ...a week, and i still don't have the manual from Ken Cook so i can wait for some suggestions on what else might work that I have in the basement....or even might be able to use elsewhere if I buy $9- wotrth?.
Water pump sealant...the blue stuff?....Permatex gasket sealer....that red stuff....?

Any thoughts?

bigred69 · Jun 21, 2010

Re: Beware the perils of silicone sealants

The best is called right stuff. Use a thin coat. It sets in a minute.

wilde1j · Jun 21, 2010

Re: Beware the perils of silicone sealants

Any good brush-on gasket sealer is OK, like Permatex Aviation, etc. The function is to hold the spaghetti seal long enough to get the deal assembled. Of course, the can will surely be a lifetime supply for you.

Philip_G · Jun 21, 2010

Re: Beware the perils of silicone sealants

lots of posts on the forum say permatex #2 is alright, sure hope they're right.

1946Zephyr · Jun 21, 2010

Re: Beware the perils of silicone sealants

I stopped using silicone and this is one of the reasons. I believe it is suitable for where water is, but not gas and oil. I prefere to use the permatex non-hardening sealer and it has worked out goood for me. Also, being moderate on the application, vs. generous is also a plus too.

Tim Frank · Jun 21, 2010

Re: Beware the perils of silicone sealants

wilde1j said:
Any good brush-on gasket sealer is OK, like Permatex Aviation, etc. The function is to hold the spaghetti seal long enough to get the deal assembled. Of course, the can will surely be a lifetime supply for you.

I use permatex all the time....it is the best plumbing thread sealer i've ever used.
Thanks....

Cofe · Jun 21, 2010

Re: Beware the perils of silicone sealants

1946Zephyr said:
I stopped using silicone and this is one of the reasons. I believe it is suitable for where water is, but not gas and oil. I prefere to use the permatex non-hardening sealer and it has worked out goood for me. Also, being moderate on the application, vs. generous is also a plus too.

A good silicone to use with gas and oil is blue silicone, available at automotive part stores.
Put it on real thin with problem gaskets, or machine surface fits. "I mean real thin" probably about .005 thick. Put some on a finger and rub it on the sealing surfaces . Wipe off the excess.

Rick. · Jun 21, 2010

Re: Beware the perils of silicone sealants

Cofe said:
A good silicone to use with gas and oil is blue silicone, available at automotive part stores.
Put it on real thin with problem gaskets, or machine surface fits. "I mean real thin" probably about .005 thick. Put some on a finger and rub it on the sealing surfaces . Wipe off the excess.

I've used permatex for years in all kinds of applications. I've used all the colors too. I have had a few instances where it helps the gasket slide out from the surfaces being mated so for sure I think twice but I believe it has it's place and is a good product. Oddly enough, I've never used it on plumbing and I'm a plumber. LOL Rick.

Beware the perils of silicone sealants

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