Boxer: engine block to trans sealer

Absolutely positively never use silicone there. It cost Ferrari a ton of money from all the blown up motors.

That oil passage is post oil filter and the silicone that gets into it (it will, have seen the outcome many times) will break off in the oil flow and clog the small passage restrictor feeding the heads. It starves the cam bearings and siezes a cam.


Use Locktite (Permatex)518

It anerobic and will not harden in oil passages.

 

Hank -- the Loctite 518 isn't a non-hardening sealer (like Hylomar paste). It's an anerobic sealer -- i.e., only the sealer in the actual joint will harden/cure. The excess that squeezes out doesn't cure (which is not true for a Silicone-type sealer, and is the problem with that type as Brian indicated). You still want to minimize the amount that gets squeezed out during clamping -- in fact, it's almost impossible to use too little . If you do a width X thickness volume calculation (say it's about 1/2" wide X .004" average thickness -- and most parts are better flatness than that), a 1/16" diameter bead is usually plenty.

 

We put it on the O ring itself and in the groove. Any oil on any of the sealing areas provides a path for leakage. It will do no harm if small amounts get into the oil passage. That is the point of using that product. I put a thin even coat on the entire sealing surface.

 

If the surfaces are in good condition, the o-ring by itself should be sufficient. When the surface has some roughness, O use the Permatex Hylomar for o-rings.

The Valeo brand Hylomar has a solvent that evaporates pretty quickly, often before you have time to assemble things. Then it can't be smoothed out.

515/518 can be used for many o-ring applications. However, when they set up, it's very firm. This is fine when an o-ring is sealing two flanges that are solidly fastened together. But, don't use it where the o-ring seal has to flex/give a bit.