Question about vacuum leaks
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Question about vacuum leaks
I made a homemade smoke tester, it consisted of a black and mild cigar 3/8" 2' vacuum hose, a sealed metal container, and an air compressor. I drilled 2 holes into the container, lit the cigar, put the plastic tip into the vacuum hose, plugged the vacuum hose into my intake manifold, put the cigar and vacuum hose in to a hole in the metal container, and blew air through the other hole. I also blocked off the front of the MAF sensor so the intake would stay pressurized. I took my oil cap off, and I have a very very slight hazy amount of smoke coming out. I'm wondering if the intake gaskets usually leak between the intake and the lifter valley? These are new gaskets that I put on about 2 weeks ago. And also, when I did leak down tests I did hear air coming out from the oil cap so I know I have a slight amount of blowby, not enough to burn oil though. So is the smoke going passed the rings or through the intake manifold gasket? What do you guys think? Thanks
Le Mans Master
Joined: May 2004
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
You should not see any smoke there at all, Seal the engine up as usual, start it and put your palm over the pcv hole and hold it there for a short time, (on a cold engine of course) then lift your palm slowly off the hole and listen for a sucking sound. If you do hear something then you have something wrong with the new gaskets
Safety Car
Joined: Aug 2002
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From: SANTA CRUZ CA
Thread Starter
Melting Slicks
Joined: Jun 2013
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I think I figured it out. I pulled the PCV valve out and put my finger over the PCV valve and it stopped coming out. I could have sworn when I did it that way the other day that it still came out...
Le Mans Master
Joined: May 2004
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
Don't get too excited, if you are putting smoke into a sealed intake area and it is making it way out of the upper crankcase area,,, You,, have a bad gasket seal. Stop & think about it, smoke going in to the intake can only escape out the exhaust thru open valves or back into the intake, also through open valves
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Le Mans Master
Joined: May 2004
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
Race Director
Joined: Apr 2002
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From: Anaheim CA
The PCV valve connects to vacuum passages inside the intake manifold that go into the ports in the intake manifold. That means that the plenum is connected to the crankcase through the PCV system. That is why the smoke comes out of the valve cover.
Le Mans Master
Joined: May 2004
Posts: 5,866
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
This is true, my earlier statement would seem incorrect but from the way I read the op he had the intake sealed off from the pcv line, that's why I specified a "sealed" intake in my post earlier. If I read wrong then Cliff has explained your seeing smoke.
Thread Starter
Melting Slicks
Joined: Jun 2013
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Yes I caught myself earlier. Lol.
Melting Slicks
Joined: Mar 2008
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From: Santa Maria, CA
So you never said why you are checking for leaks. I've had an intake gasket leak into the lifter gallery. I knew there was a problem because the engine barely ran. After that I changed the way I installed the intake to prevent the gasket from sliding while torqueing the bolts.
Thread Starter
Melting Slicks
Joined: Jun 2013
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Likes: 39
So you never said why you are checking for leaks. I've had an intake gasket leak into the lifter gallery. I knew there was a problem because the engine barely ran. After that I changed the way I installed the intake to prevent the gasket from sliding while torqueing the bolts.
I installed bigger headers when I fixed the engine and I've never had it backfire on decel before when it was running normally. As I'm being told now by some people is that it's normal with free flowing exhausts.
And I thought the backfire was from the vacuum leaks. Fixed the vacuum leaks and it still does it. And the engine runs nice and smooth, AFR is in the okay zone. Fixed my tiny exhaust leaks and it's still there. Guess it's just something I'll have to deal with.
Safety Car
Joined: Jan 2004
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So you never said why you are checking for leaks. I've had an intake gasket leak into the lifter gallery. I knew there was a problem because the engine barely ran. After that I changed the way I installed the intake to prevent the gasket from sliding while torqueing the bolts.
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
First apply a thin coat of gray RTV to the side of the gasket that contacts the head. Place the gasket on the head where you want it to be. Then carefully place the intake on and start the bolts. I snug all the bolts and then torque to 10 ft-lb stating with the center bolts and working out. Let the RTV cure for 24 hours and remove the intake. Now apply a healthy bead of RTV to the rails and a thin coat on the gasket. Install the intake and torque per the manual. Make sure that you can see RTV squeezed out on the rails.
Thread Starter
Melting Slicks
Joined: Jun 2013
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Likes: 39
I don't know of an article. But here's how I do it.
First apply a thin coat of gray RTV to the side of the gasket that contacts the head. Place the gasket on the head where you want it to be. Then carefully place the intake on and start the bolts. I snug all the bolts and then torque to 10 ft-lb stating with the center bolts and working out. Let the RTV cure for 24 hours and remove the intake. Now apply a healthy bead of RTV to the rails and a thin coat on the gasket. Install the intake and torque per the manual. Make sure that you can see RTV squeezed out on the rails.
First apply a thin coat of gray RTV to the side of the gasket that contacts the head. Place the gasket on the head where you want it to be. Then carefully place the intake on and start the bolts. I snug all the bolts and then torque to 10 ft-lb stating with the center bolts and working out. Let the RTV cure for 24 hours and remove the intake. Now apply a healthy bead of RTV to the rails and a thin coat on the gasket. Install the intake and torque per the manual. Make sure that you can see RTV squeezed out on the rails.