Intake Manifold Leak Question for 1970 Deville
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500, 472, 425, 368 Discussion, Intake Manifold Leak Question for 1970 Deville in Cadillac Engine Technical Discussion; I recently purchased a 1970 Cadillac Deville convertible and I have been fixing it up. You can see my thread ...
  1. #1
    klinebau is offline Cadillac Owners Member
    Automobile(s): 1970 Deville Convertible Red
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    Intake Manifold Leak Question for 1970 Deville

    I recently purchased a 1970 Cadillac Deville convertible and I have been fixing it up. You can see my thread here: http://www.cadillacforums.com/forums...c-deville.html

    I have been focusing on getting the engine in good running condition first. Recently I ran into an issue that I need some advice from the engine gurus. I decided that there is an oil leak on the drivers side intake manifold.corner At first I thought it was the valve/rocker arm cover and I replaced the gasket (it was leaking onto the exhaust mani). I do not believe the valve cover is leaking anymore but oil seems to seep up from the corner of the intake manifold underneath where the high-tension wire plugs into the coil. According to my torque wrench, most of the bolts were not loose (except for the two in the center where the inlet is for the exhaust), but I did crank them a tiny bit just to see what would happen.

    After cranking the bolts a bit, I took the car for a 4 mile test drive. When the car warmed up, the idle was suddenly much higher than it was previously-- to the point where it will accelerate to 30 mph without throttle input and slams into gear if you shift the transmission into drive. My question is this: Is it possible that I have a vacuum leak from the manifold and now when the car warms up, the leak gets sealed? Also, is it typical to see an oil leak from the intake manifold? I am prepared to replace the manifold gasket, but I want to make sure that is the correct response and would like advice for the best way to seal it so that I don't have to do it twice. The gasket kits look like they come with a rubber section for the front and back. Is it advisable to use RTV instead of the rubber? I do not believe that I have a fuel problem since I have already replaced the carburetor, throttle linkage, choke, all of the vacuum hoses and the fuel line (filters are clean). The car runs pretty well and I didn't even suspect that I had a vacuum leak prior to this.

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  3. #2
    cadillac_81 is offline Cadillac Owners Member
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    I would just replace the manifold gaskets, the rubber gaskets that goes to the front and back of the manifold when you out em on make sure you out rtv on the corners of em, i did a manifold gasket on my car last week cleaned up the manifold and it runs great! The rtv i used is the right stuff it does wonders!

  4. #3
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Intake Manifold Leak Question for 1970 Deville

    Spray carbonator cleaner through the little red plastic tube supplied with the can to prove or disprove manifold leaks.

    Repeated cleaning of the suspected oil leak area followed by a small goober of RTV silicone will stop the oil leak if you don't find the manifold needs to come out.

    If you do change the intake gaskets use the rubber supplied.

    Oil leaks are NOT common on these engines except through failed oil pressure gauge senders.

  5. #4
    klinebau is offline Cadillac Owners Member
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    Thread Starter

    Re: Intake Manifold Leak Question for 1970 Deville

    Thanks for the replies. I'll try this test for vacuum leaks when I get a chance. I already ordered a new gasket, but I may wait to replace if there are no vacuum leaks. I'll post up what I find.

  6. #5
    klinebau is offline Cadillac Owners Member
    Automobile(s): 1970 Deville Convertible Red
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    Thread Starter

    Re: Intake Manifold Leak Question for 1970 Deville

    I replaced the gasket over the weekend. I didn't have any vacuum leaks, but the oil leak was bothering me. It wasn't a very difficult job, just a lot of stuff to remove/move. Also, it was time consuming to clean and prep for the new gasket. The new gasket is on now and not leaking! I still have to re-torque since it has heat-cycled once.

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