Lower Intake Leak - Any suggestions?

[TheUser]

I pulled and reinstalled my lower intake a few weeks ago because it was leaking oil out the back. I read opinions and found that a lot of guys forget the gaskets for front and rear and just use a nice bead of silicone. I used Ultra Copper permatex for the front and rear and now it's leaking again with 12 miles on the motor. This time, I plan to use gaskets (held in place with high-tak) and i'm also going to use Michael Yount's idea of cutting the heads off of some bolts to use them as dowels to line the intake up correctly. Other than those ideas, does anyone have any other advice? I know this isn't very hard to do, but I'm just not sure why it's leaking on me

One of my bolts on the left side towards the back won't tighten...I was torquing them down, heard a snap and it wouldn't tighten, but the bolt isn't broken, so maybe that's part of the reason, although I doubt it.

 

[Michael Yount]

What level did you torque them to? The snap doesn't sound good - I'd pull it back apart and see what you find. If it snapped and then wouldn't tighten, I'd expect either a broken bolt or a broken intake. There's no reason to torque any tighter than 16-18 ft-lbs.

The use of silicone on the front and rear of intake manifolds originated when people realized they had to change that gasket thickness when heads were milled or blocks were decked. Those machining changes caused the manifold to sit closer to the block - but the stock cork gaskets wouldn't let the manifold sit closer - so sometimes manifolds were broken, or leaks occurred as people tightened them down - and the gaskets held the front and back ends of the manifold too high. A simple bead of silicone allowed the manifold to squeeze down to the height it needed to be at to seal against the heads.

If your heads haven't been milled or your block hasn't been cut, I'd use the stock rubber end seals provided by Ford (others probably have them too). You probably can't buy them alone - they'll come with new lower intake gaskets. They have tabs/lips which fit into/around the block sealing surface which hold them in place as you tighten. You clean the block and manifold, apply some light grease to both sides of the rubber seal so that when you're tightening, the gasket can slide without binding; and a dab of rtv at the corners (the block/manifold/head interface) to be sure they seal.

My second choice would be the cork gaskets that come in so many kits - again, clean everything, and then I'd put a light coat of rtv over the entire cork gasket (inside, out, top, bottom), and dab at the corners. Watch very closely when tightening to see that they don't squeeze out of position, especially the back. I would only use a silicone bead to seal the lower if I had no other alternative. Just my experience with it.

 

[04sleeper]

I've used Blue RTV Silicone on the front and rear of the intake for about 15 years now on all my cars that I've worked on. Never leaked yet. Just had to make sure it was completly dry before starting the motor.
Also, what kind of intake gaskets do you run by the way. Iv'e always had good luck with Felpro 1250's.
I would definately look into that rear bolt issue. It is not going to fix itself or get any better.
Another idea is to go over the torque sequence a few times. Just to make sure the intake seats properly.
Good Luck!

 

[TheUser]

Thanks guys. I torqued, I believe to 18 lbs, nothing too crazy. I also torqued in like 3 stages and double checked to make sure all were good. The one just snapped and the bolt is fine...I thought broken bolt as well, but nope. I'll inspect when I pull the lower back off today. I let it sit for a couple days last time when I used just the silicone. It seems to only blow out when when I go high-rpm.

I have the cork gaskets from the fel-pro kit, so I guess i'll use those and try to reuse the intake-to-head gaskets.

 

[Michael Yount]

If it's high rpm related - do you have too much crankcase pressure? Is your pcv system working correctly?

 

[04sleeper]

If it's high rpm related - do you have too much crankcase pressure? Is your pcv system working correctly?

Thats what I was thinking. Holeshot me.....

 

[TheUser]

pcv is what I thought of before I posted, but I did put a new screen and pcv valve in last time...don't know why it wouldn't work properly. If it is pressure though, I would assume it will continue no matter how well I install the lower intake.

 

[Michael Yount]

Depends on how much pressure - but, if the lower intake holds and it is excess pressure, then it will find other outlets - blowing the dipstick out, rear and front main leaks, valve cover gasket leaks, etc. How many miles on the motor? Any other oil leaks or consumption? Have you run cranking compression or leak down tests to check the cylinder sealing integrity?

 

[ratrapp]

i worked at a mopar dealership for almost 5 years and the mopar rtv black sealant is the best in the business.i do agree it sounds like you have too much crankcase pressure.my 5.0 does the same thing.i replaced the pcv valve and screen also but it didn't help.my motor keeps popping the rear mainseal out and pushes the dipstick out at high rpm.it's probably like mine and needs a rebuild.

 

[TheUser]

I have checked compression and it definately needs a rebuild. Last time, #5 was like 70 psi and the others were 125-150ish, but I was just gonna drive it like that. The lower intake is the only oil leak that I know of and I plan on fixing it today. The motor was rebuilt supposedly 6000 miles ago and I replaced the head gaskets not even 50 miles - 6 months - ago. As far as I can tell, it doesn't blow any smoke. Would one of those screen filters for the oil filler on the valve cover be a good idea? I've heard they get oil all over the engine bay