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#1
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Sealing BB intake manifold & Thermostat housing
I need some advice on sealing the intake manifold on my 1968 383. I usually use black RTV sealer around the ports and on the ends, but have had some leakage after a short time...... So, what is a better way to seal the intake?
Also, what is the best way to seal the thermostat housing? I have a factory iron water pump housing with a Milodon high volume pump, and a high flow thermostat. I have used the factory thermostat housing as well as a thick chrome aftermarket piece and have the same result: leakage from the gasket... I have used several gaskets along with some black RTV. What else can I try? |
#2
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Where are the leaks on your intake? Are they oil leaks or vacuum leaks or both?
I usually try not to get any of the RTV to the inside of the embossed area on the intake gasket so I can be sure not to have material squeeze out into the port. They make RTV that is fuel resistant and you should be using that if you're not already. I have had good luck with thermostat housings by waiting until the RTV is fully cured (a day) before putting any water in it. |
#3
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I am getting oil into the intake ports, but never seemed to have a vacuum leak problem. At idle I normally held about 12.5" of vacuum.
As far as the thermostat housing is concerned, I always used black RTV along with a gasket. Do you recommend not using the gasket at all? |
#4
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I've done the thermostat both ways successfully.
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#5
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the only stuff that works for me is the foam sealant in a can, works great and instantly.
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#6
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On sealing the thermostat housing/water neck:
Mating surfaces should be spotless, with few or no pit marks. Sealing surface of water neck should not be warped. If it is, get a new cast iron one at parts store. Black RTV or Ultra Copper works well for sealing. No biggie here, just gotta make sure the sealing surfaces are good. I usually apply sealant to both sides of a good gasket, let it sit for a few minutes, then assemble everything. Let assembly sit for 3-4 hours before adding your coolant. On the intake - if you run a full valley pan: Using a brand new valley pan, apply fuel/oil-resistant silicone around intake ports, both sides. You want to create a slightly-raised "bead" of the stuff, sort of like the fancy Fel-Pro intake gaskets. Let the sealant FULLY cure. I'd give it 3-4 days at normal room temperature. Install pan like normal, with a bead of the same sealer at front and rear block rails, and in the corners. Install intake. Take your time. When you get it aligned, torque bolts in proper pattern/sequence, in steps. Run motor. If intake is aluminum, keep a torque wrench handy and check it a few times after initial install. Heat cycles tend to loosen intake bolts. On the sealer: do a search here for "Right Stuff". It's a sealer that PRO mentioned, I believe, as being real good for intake sealing. Good luck |
#7
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I've always had excellent results with hylomar on the intake ends, and coppercoat around the runners.
On the theromostat housing I agree on the surfaces being spotless, but I also us the heavy steel housing. I find the aluminum will warp. |
#8
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For the intake, I've always used the brush tack that comes with the Fel-Pro valley pans. I've never had a leak.
For the thermostat, I used some Permatex brush tack on it, about 18 months ago (when I replaced the T-stat). It hasn't leaked. |
#9
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Here is a link to our general instructions for installing an intake manifold.
Intake Manifold, installation instructions I would recommend not using a aluminum valley pan for a gasket. You can buy the standard paper type gaskets and get a seperate valley cover. Using the Gasgacinch with a standard type gasket works really well, but just don't use silicone with them or the gasket will move. I am not a big fan of a valley pan. I had one on my boat that had a 455 olds. RTV can get messy, and if you aren't careful, it can squezze out and get into the engine, or block the intake port a little. |
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