Oil Leak From intake manifold gasket

[87sierra]

Okay its been a while since i have been on here i have replaced my intake manifold gaskets two times and everytime due to oil leaking from them at the back and front of the intake (Valley of Engine) and everytime it stops leaking for two to three weeks than starts leaking again i properly clean both surfaces making sure they are clean of oil and are smooth then apply the right amount of silicone to the surface i believe they recommend a 1/8 on an inch of silicone not sure if that is right then i place the intake down and and thread all bolts in and work from the center out in a circle pattern torque the bolts to the proper spec i have also notice with the intake off that were the egr valve is on the intake that the passage on the head is blocked by a thin layer of what looks like carbon but is as hard as rusty sheet metal. I dont think that is the cause of my leak could a possible bad pcv valve be the cause? just wondering if anyone had any ideas as to why the intake gaskets keep leaking or if there is a different style of gasket that can be used i know there is a style that uses rubber pieces for in the valley or between the intake manifold and the block here is a link to the gasket set i use http://www.napaonline.com/Catalog/C...-Gasket-Set-Intake-/_/R-FPBMS93317_0147289129 i usally use the silicone supplied with the kit unless i have a tube of silicone i get from work
Thank for any help

 

[MrMarty51]

If the PCV valve rattles when removed from the valve cover, with the engine running, it is working as it should.
I really like the gasket kits with the valley gaskets. Silicone in the corners of the side gaskets to the end of the valley gaskets.
Tricky getting the manifold set down without causing one or both end gaskets from dislodgine but, thats the fun of it all.

 

[firebane]

Should be 1/4" bead for intake manifold on front and rear walls. Then make sure you torque it down and let it sit overnight unless your in a rush.

Also don't forget the thread sealant.

 

[87sierra]

i will check the pcv valve tomorrow if i have time i wasnt sure if that style gasket kit would work for my engine since it is tbi and not carbuerated dont know if that makes a differnes since they have different intake manifolds other wise i would go that route

 

[87sierra]

okay i thought i was wrong on the amount of silicone the said to put on since i replaced them last summer and i am certain i layed a 1/4" bead of silicone down from one paper gasket to the other i just couldnt remember the thickness off the top of my head the first time i did them i was in a rush and the second time i left it sit for at least 2-3 hours then had to go some were but they always seem to not leak for 2-3 weeks which makes me think there is to much pressure in the engine since also at every rubber grommet on the valve cover there is oil sepping out even the oil fill cap is like that

 

[firebane]

okay i thought i was wrong on the amount of silicone the said to put on since i replaced them last summer and i am certain i layed a 1/4" bead of silicone down from one paper gasket to the other i just couldnt remember the thickness off the top of my head the first time i did them i was in a rush and the second time i left it sit for at least 2-3 hours then had to go some were but they always seem to not leak for 2-3 weeks which makes me think there is to much pressure in the engine since also at every rubber grommet on the valve cover there is oil sepping out even the oil fill cap is like that

Make sure your PCV system is working properly. Breather on one side and pcv valve on the other side.

To much pressure is a bad thing.

 

[87sierra]

Thats what i figured once that is fixed if the pcv is the problem then i will replace the intake gaskets a gain when it is warmer out since i have to do it outside maybe i will even take the hood off that might make it easier since buying a quart of oil a week is killing my wallet

 

[MadOgre]

So I assume you have a cast iron intake ? not an after market one ?

1/4"-3/8" of silicone wide and high, making sure to get a little under and over the little tabs on the intake gaskets where they meet the valley.

Let the silicone set for 20 min before placing the intake. Once you have placed the intake install all the intake bolts with some silicone on the threads of the middle runner bolts, and snug but do not tighten. after an hour tighten them down but do not torque.

Let that sit over night and then torque and re-torque. After running the engine for its first hour after installation re-torque again. After a few more days of running the engine re-torque again.

 

[87sierra]

So I assume you have a cast iron intake ? not an after market one ?

1/4"-3/8" of silicone wide and high, making sure to get a little under and over the little tabs on the intake gaskets where they meet the valley.

Let the silicone set for 20 min before placing the intake. Once you have placed the intake install all the intake bolts with some silicone on the threads of the middle runner bolts, and snug but do not tighten. after an hour tighten them down but do not torque.

Let that sit over night and then torque and re-torque. After running the engine for its first hour after installation re-torque again. After a few more days of running the engine re-torque again.

Okay thanks for the info yes it is a cast factory intake not aftermarket

 

[DoubleDingo]

Not sure if you mentioned which type of silicone you used. Use black. I used blue and it leaked. Grey is okay, but black is better for holding up to oil. I learned that from the parts store guy who did a vortec swap and ran into the same problem I did. I swapped in vortec heads and intake last year, and the blue lasted for a while, but then developed a leak. I couldn't locate the leak and I suspected it was my rear main so I pulled the engine and re-sealed the whole engine from bottom to top. When I pulled the inspection cover I realized it wasn't the rear main and I really didn't need to remove the engine, but I went ahead and pulled the engine anyway to re-seal it. Just sharing what I did to mine, not recommending you pull the engine. One thing you might do once you remove the intake and have the mating surfaces cleaned up, is take a cold chisel and score a line along the back of the block between the heads where you apply the sealant, that gives it something to bite into. The score doesn't need to be deep, just a line down the middle. On my application I found out the back of the intake has an odd curve that doesn't follow the curve at the back of the block very well, and there is very little metal for sealant to adhere to where the oil pressure fitting goes, so I added extra to the back once I had the intake torqued down. I hate leaks! Thus far, the Ultra Black has held up much better than the blue.

 

[MadOgre]

I used Blue on my intake valley and it held up just fine for about 5 years with no leaks.

The trick is to put enough silicone on that when you set the intake it pushes the RTV out from between the 2 mating surfaces and spills over the walls a bit. That way it is thicker on either side of the mating surface, and when it is dry it is then locked from pushing out.

Also the other trick with RTV is to apply it, then place your mating component with out torqueing it down and allow the RTV to dry this way. Then when you go back and torque it down it will now compress the dried RTV for a better seal.

 

[DoubleDingo]

I didn't know one color was better than another until I talked to that guy from the parts store. I still use blue but not for my intake or anything that needs to hold oil under pressure like an engine.

I like the idea of letting the rtv set up some before torquing things down.

 

[350runner]

I've found it best to index finger a skim coat of rtv on and letting that set then going back with a thick bead.

Sent from the dust in front of you!

 

[bucket]

I like using the Ultra Black too. I've also never let the RTV sit more than just a few minutes before bolting it together and often running the engine an hour or two later (depends on what motor). After who knows how many hundreds of intake gaskets jobs, not a single one ever leaked. There shouldn't really be any pressure behind it.

I'm leaning towards defective PCV system, along with possibly another issue. Oil splashing past the intake can't possibly be responsible for losing a quart of oil every week. It's sounding to me like there might be a lot of blow-by.

 

[flyboy1100]

Oil splashing past the intake can't possibly be responsible for losing a quart of oil every week. It's sounding to me like there might be a lot of blow-by.

I think this is my problem, i use 1qt every 400 miles or so. 99% my intake leaks at the back. Oil sender etc are dry.

After 1500 miles my oil breather is dripping oil. I would like to fix it, but at the same time it is a tired old 305 so a used engine sounds better


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