Oil leak rear of engine - why? and reuse intake gaskets? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-02-2006, 02:02 PM
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Oil leak rear of engine - why? and reuse intake gaskets?

I have an oil leak at rear of enginge (sbc 350). It looks like it's from the rear valley gasket of intake manifold. I recently built the engine - about 4 weeks ago and I guess I didn't get it sealed well.
First question - kinda basic, but I've never really thought about it until now. There's about 3-4 in between the top of the block and intake manifold. There isn't any high pressure at the interface between manifold and block - just the oil draining down from heads. The question is - how does enough oil get that high with enough pressure to leak out? I can't believe the oil fills up the valley that high. Is it just that the air in engine is filled with oil mist and air moving through the leak in gasket pulls oil with it?

Second question - I have blue Felpro intake gaskets which came in an Felpro engine rebuilt gasket set. The gaskets look fine - can you reuse them?

Thanks
Ed

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Old 12-02-2006, 02:24 PM
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Not sure of the physics of it, but the lifters are flinging oil and for some reason it finds it's way out of there. The valley does not fill with oil.
I personaly would not reuse them, not worth it to me if it doesn't seal and it has to be disassembled to replace.
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Old 12-02-2006, 02:30 PM
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I would buy new felpro gaskets.
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Old 12-02-2006, 04:14 PM
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Buy new gaskets and be sure both intake and heads are clean and oil free at gasket area.Take the end gaskets that fit across front and back of intake and throw them as far as you can. Put a good 1/4 inch of silicone gasket maker preferable the blue in it's place. put side gaskets on dry or use very thin coat of high tack gasket glue.This will give you the best seal you can get and allows intake to seat better than using end gaskets.
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Old 12-02-2006, 04:40 PM
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Oil gets flung all over the place inside an engine. Combine a little bit of blowby with a poor sealing gasket and small amounts of oil that may collect in various crevases, nooks and crannys and you've got yourself a leak.

Put new intake gaskets in, a good set really isn't that expensive and not worth pulling the intake and distributor out a second time if the existing gaskets leak after resealing the engine.
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Old 12-02-2006, 04:53 PM
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Thanks for replies. I will get new gaskets. I had used the rubber end gaskets with some silicon sealer - but obviously it didn't work well. I'll try silicon without end gaskets this time.
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Old 12-02-2006, 06:24 PM
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Quote:
Originally Posted by sabino56
Thanks for replies. I will get new gaskets. I had used the rubber end gaskets with some silicon sealer - but obviously it didn't work well. I'll try silicon without end gaskets this time.
Yes, many people junk the end rail gaskets and go the RTV route.
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Old 12-02-2006, 08:23 PM
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Are you sure it's the intake gasket? There is an oil plug on the back of the block which can weep.
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Old 12-03-2006, 12:27 AM
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Pretty sure - I could see where it was wetting out in the back - right next to the oil pressure sensor. A first, I thought it was it but unfortunately it wasn't.
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Old 12-03-2006, 11:19 AM
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Quote:
Originally Posted by sabino56
Thanks for replies. I will get new gaskets. I had used the rubber end gaskets with some silicon sealer - but obviously it didn't work well. I'll try silicon without end gaskets this time.

Rubber gaskets and silicone sealer don't mix..... use one or the other....... I prefer straight silicone.

I like to use an 1/8 drill and drill shallow holes about 1" apart along the "china wall" for the silicone or gasket to grab into so it won't slide out. You can do the same thing to the intake manifold if you wish. Some people just use a center punch to make dimples. It works. Always do it.
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Old 12-03-2006, 11:29 AM
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Quote:
Originally Posted by xntrik
Rubber gaskets and silicone sealer don't mix..... use one or the other....... I prefer straight silicone.

I like to use an 1/8 drill and drill shallow holes about 1" apart along the "china wall" for the silicone or gasket to grab into so it won't slide out. You can do the same thing to the intake manifold if you wish. Some people just use a center punch to make dimples. It works. Always do it.
I can't second what xntrik said about using silicone with rubber enough. Don't do it! I have used the center punch method on end rails before and can say it does work. Always use new gaskets and check your end gap. In your first post you state the gap is 3/4". If so that is way too much. Did you mean 3/8"? How much were the heads/block milled? You may have to have the intake milled as well.

Barry
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Old 12-03-2006, 12:21 PM
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Quote:
Originally Posted by topfuel
I In your first post you state the gap is 3/4". If so that is way too much. Did you mean 3/8"?
The gap is small. In the first post, I was trying to say the distance between top of end rail and valley was 3" to 4" and I was wondering how oil even got to top of rail to lead out.

Thanks for advice on not mixing rubber and silicone. I pulled the manifold off and found the rear rubber gasket torn in area that oil was leaking. I guess I could have torn the rubber gasket when removing the manifold but since it's right at area of leak - it seems that was the problem. How it got torn - I don't know...?

Ed
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Old 12-02-2007, 01:33 PM
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rear intake oil leak

I have a new zz4 350 chev engine and have had 3 intake manifolds leak a the rear --have used grey rtv permatex high temp silicone on the ends have even pick punched the block and the manifold ends as has ben suggested --still leaks at the rear on the passanger side where the manifold turns up by the head I'm at wits end!

Last edited by ken hinton; 12-02-2007 at 06:09 PM.
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