Lower intake manifold gasket or silicone?

Discussion in 'Fox 5.0 Mustang Tech' started by ponsai03, Jul 11, 2009.

  1. I'm in the process of installing my lower/upper intake manifold on my 1990 5.0 LX.
    I've read in this forum not to use the cork gaskets that mates between the block and the lower intake in the front and rear of block (I think they are the "S" shaped ones) and use silicone instead.
    Is this true or should I use the gaskets. Thanks
  2. A little silicone has always done the trick for me, cork end gaskets not so much. Just got to be careful to use some good quality stuff like aircraft sealant and don't use a whole lot. What's interesting is that the stock Ford gasket set on an Explorer uses rubber end gaskets and those seem to work very well too. Not that there is anything wrong with RTV, but formed rubber gaskets would look a little cleaner. :D
  3. regular black rtv around the coolant ports, just put a skim coat(smear it with your fingers) to get a slight film to aid in sealing this area it's prone to leaking by the gaskets. I and many of the members on here and other forums use "right stuff" by permatex, comes in a can that allows you to apply a bead under pressure. apply about a "1/4 bead across the block and about "1/4 up the head, also dot the 4 corners where the head meets the block before applying the intake gasket to seal this area( it can be open under the gasket allowing for a leak). Don't use the permatex right stuff around the coolant ports, it's very thick and hard to squash down in this area, very good for the ends of the block and big areas.I haven't had a leak yet.have fun :nice:

    permatex right stuff..

  4. Thanks you guys for your help.
  5. A million times NO to the cork gasket! :)
    Yea, even with my old Olds V8, the cork gaskets were a bad idea.
    In general, a good quality rubber from the manufacturer gasket that is held in place with a light coat silicone is "okay". A big problem with the rubber gaskets is that they have a tendency to move/squirm if the intake is not put on "in just the right manner, from the correct angle, etc". So, with the advances in silicon sealers over the years, it's best to go with just silicon.

    IMHO, all cork gaskets are pure cr*p. :)

    Make sure you get a brand name silicon! Do not use the generic cr*p that many parts stores sell! IMHO, use Permatex or 3M stuff only.
  6. My two cents worth...

    Whatever you do, don't skimp on cleaning the gasket surfaces. New gaskets need to seat against bare metal and not the residue left from the old gaskets in order to seal leak free. This is the most time consuming and tiresome part of the job. Put some cardboard in the lifter valley to help catch the gasket scrapings. Have a shop vacuum handy to suck up the scrapings and any coolant that leaked into the lifter valley.

    My favorite trick that saves time and effort is the stay in place gasket. Be sure that you scrape (don't use a wire brush) all the old gasket material off, then clean all the surfaces with acetone or MEK.

    When the surfaces are clean, use weather strip adhesive on the head to manifold surface, and on the side of the gasket that mates to the head. Follow the instructions on the tube or can and when it gets tacky, press the gasket down on the head.

    Clean the area where the rubber rails mount to the block in front and in the rear with more acetone or MEK and do the same trick with the weather strip adhesive that you did to the heads.

    Coat the rubber seals and the gasket area around the water passages with a light coat of Permatex Blue Silicone gasket sealer and put it together. Whoopee! no leaks, and no gaskets that shifted out of place.
  7. what about that indian glue/gasket stuff?
  8. Most of the good Fel-Pro intake sets now come with rubber end seals, that have lips that overhang the end rails of the block, so they don't squeeze out. They are great, they work just as good as silicone, and it's more simple, cleaner, and faster. I have no issues with those on my 302 or my 351w.
  9. I use Indian Glue to hold gaskets in place. Such as if I was using a rubber gasket for the intake, or to hold the gasket for a thermostat housing.

    Indian Glue isn't a silicon sealer and is thin and must be put on thinly. So, you could never use it in place of a regular gasket (rubber or cork).

    Silicon sealers can be better than Indian Glue in some applications because Silicon will better fill in voids, nicks, and scratches - as what often happens to the mating surfaces of a thermostat housing and the intake. However, Silicon sealers will allow gasket squirm. Because you can not wait until the Silicon sealer fully dries on on part of the assembly. And, if you wait until it just starts to skim (as some recommend), then the gasket can still squirm and get out of place.

    Valve covers and their gaskets where there's a trade-off in using silicon or Indian Head to hold on the gasket in place. It all depends what works for a person and in a specific case. :)
  10. I always forget this but when you put silcone around the water ports do you put it inbetween head and gasket, or intake and gasket?
  11. the head and gasket but it doesn't hurt to do both, just use a light coat.
  12. x2 on the permatex right stuff!! bout 15 dollars for a can but put a little on your fingers and u can tell its way better than the average silicone. Did my intake about 2 mos ago and no problems!!