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post #1 of (permalink) Old 12-02-1999, 10:36 AM
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Oil in the upper intake

Hi all, I recently replaced my valve cover gaskets, '88 Bronco, 351w, (what a bear!). During the process of replacing the passenger side I had to remove the upper intake manifold. I found oil in the last tube of the intake (closes to the firewall). The PCV valve seems to be working, but I can't figure out where the oil may be coming from. Any info. would be appreciated. Thanks in advance.

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post #2 of (permalink) Old 12-02-1999, 05:41 PM
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Re: Oil in the upper intake

If the suction port for the PCV system is into the throttle body, it could be oil that's migrated from the valve cover, up through the hose and PCV valve in the airflow from the valve cover. Some valve covers have a baffle inside that stops oil from splashing from the rockers directly up to the hole where the hose connects. And some engines don't.
Just got done working on a Chrysler 3.3L V6 that doesn't have a baffle (pulling the hose out, and looking through the grommet into the valve cover, could see the rockers directly. With a baffle, you can't). The hose tends to absorb oil over time, and with engine heat, cooks it to stone. Grommet usually hardens up too. Just the way it is.
Have seen 302's with a baffle, but even then there is still some oil migration. Just not real noticable, as it goes into the lower manifold.
These comments are assuming you're seeing a LITTLE bit of oil. If you've got a gusher, then I don't know!
I can't remember for sure exactly where the 351 intake-side suction port is, and my Bronc isn't with me at the moment.


post #3 of (permalink) Old 12-02-1999, 08:25 PM
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Re: Oil in the upper intake

Hi UncleDon, interesting, the PCV airflow is connected to back of the upper intake. I do recall seeing the baffle when I cleaned the valve cover. However, I didn't bother to inspect the hose or gromment, they looked find at the time (but I'll double check). Makes sense... Oil began to drip when I set the intake aside. It's funny, though, that port was the cleanest of all of them. The rest had carbon build-up. Question, does the PCV connection at the intake work like a vacuum? If it does, then I can see how the oil is getting up in the manifold. Thanks a bunch...

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post #4 of (permalink) Old 12-03-1999, 08:31 AM
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Re: Oil in the upper intake

Yes, its a vacuum source. Flow path is in through filter in the air box (my '94 has a separate PCV fresh-air filter under the main air filter), through the fresh-air hose to the left valve cover, through engine picking up blow-by gases from the crankcase (and picking up a bit of oil from the right rockers!), then out through hose & PCV valve to intake. Since you saw the baffle, I guess that's just the way it is. I haven't taken the upper intake off the 351 (yet!), but when I do I'll probably find just what you did.

I was wondering... when you took your valve covers off, did they have cork valve covers with little bits of metal rod (2 under each bolt-head area) pressed into the gasket? I worked on a '90 302, and it was one of the dumbest ideas I ever saw. The pieces of metal helped stop the gasket from being compressed too far under the bolt heads. Old gasket, lots of little pieces of metal coming loose, in an open valve train area. When I realized it, I counted them all. I was short 2 of them. Uh-oh. Looked everywhere around the valves, intake, etc. finally found one on the floor. One still missing, presumed down to the crankcase. Oh good! But found it on the floor later in cleaning up! What a dumb idea!

post #5 of (permalink) Old 12-03-1999, 04:13 PM
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Re: Oil in the upper intake

UncleDon, yes it did come with cork gaskets and they had two bits of metal rods at each bolt area ( I agree it's not too effective when it comes to replacing them). They were a bear to remove because the gaskets stuck to the heads. I made a mess and used my shop vac to vacumm all the bits and pieces that fell on top of the head. A fellow bulletin board member sold me some great gaskets from FORD. They're metal with rubber of both sides. So far they're working great. I'm slowing trying to replace all of the gaskets. Thanks for your response.


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