Classic Mustangs (Tech)Technical discussions about the Mustangs of yester-year.
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I use RTV instead of the cork "end seals". A very popular practice and one of the very few places I like to use RTV. Brand/type of RTV doesn't matter too much and this isn't a very high heat location. I've had luck with Permatex brand RTV myself, LocTite is certainly also a good brand. I don't use "Gasgacinch". I do use Permatex "aviation" sealer on the water ports only of the intake gaskets. I have had the very best luck with this particular sealer for more than 10 years on a WIDE variety of gaskets. I use just a thin coat of this sealer on these areas. I apply the extra sealer because I've had a few failures in this area and believe it's needed though FelPro recommends no sealer. I believe the problems may in part be caused by the different expansion rates of the cast iron block and heads versus the aluminum intake. Though cast iron intakes aren't immune either. While the engine is running, you might be suprised to find the intake actually cool to the touch while the heads will burn your finger. The Aviation sealer is quite tolerant of all this expanding and contracting as it never quite hardens. Old Harleys are very prone to such expansion problems and have a reputation of leaking. Mine is 32 years old and does NOT leak. Guess which is the only sealer allowed near it.
My old 351W once sprung a leak at the left front water port, so did a 289 and a 302. I recently helped a friend replace his S10 4.3 intake gaskets because of a leak at the exact same spot. And last month my wife's 4.0 Explorer surprised me by springing a leak in the exact same place. All these examples had at least 100K miles on them and no evidence of ever having had any extra sealer. So this seems to be a common problem and not just with Ford V8's. I've never seen anyone recommend using any sealer around the intake ports and I've never seen the need for it either.
Anther thing I highly recommend is to use "installation studs". Some Fords came with studs at four corners of the intake, most seem to use just all bolts. I made some by taking 4 extra bolts, cutting the heads off, and then rounding the ends a bit. Loosely install one in each corner of the block after you get your gaskets all set and your RTV laid down. Then you can put your intake over the studs and just plop it straight down. Start some bolts and pull your studs back out. If you've ever put an intake on without doing this you can probably see the value. No wiggling the intake around trying to align bolt holes and messing up your carefully aligned gaskets and RTV. Just PLOP and bolt it down. It's worth destroying four bolts for.
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