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Thread: 350 chevy coolant leak head gasket or intake

  1. #1
    Mitsu booster
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    350 chevy coolant leak. Head or intake gasket?

    91 chevy 350 tbi. Buddy thought it was an intake manifold gasket so, he bought one to have me do it. Well, I say its possible that it could be a small head gasket leak.

    I let her idle, gave it some revs and the temp gradually shoots up 213*. Shut her off, looked under the truck and there's a small puddle on the ground passenger side towards the rear of the engine. Dip stick looks/smells like normal oil. Pulled the valve cover off and sure enough, chocolate milk. I even looked/smelled the exhaust for the hell of it. I couldn't smell coolant and I couldn't see any color change, just very white.

    EDIT: I did 2 more tests. The coolant in the rad has a constant bubbling. I think this next test indiactes if the intake manifold gasket is bad. I let the engine idle and then removed the oil cap to see if the idle changes and it does not. I think the head gasket is partially blown and the coolant is trickling down the passenger side head. But, then why would I have coolant mixed in my head and not on the dipstick?
    Last edited by menace2society; 05-02-2009 at 08:35 PM.

  2. #2
    The moderately moderate moderator Turbo Mopar Staff black86glhs's Avatar
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    Re: 350 chevy coolant leak head gasket or intake

    One of 2 possibilities. You either have a cracked head or the intake gaskets are leaking.
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  3. #3
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    Re: 350 chevy coolant leak head gasket or intake

    Quote Originally Posted by black86glhs View Post
    One of 2 possibilities. You either have a cracked head or the intake gaskets are leaking.
    I agree. Although, I think it would be tough to crack a 350 head. Maybe warping is more common.

    Well, I'm now starting to believe it actually is the intake gasket. I looked at the head and intake manifold more closely and see that the coolant passage ways on the manifold are really close the lifter holes. So, when the intake gasket blows, the coolant instantly mixes with the oil. Which explains why the top of the head and valve cover is completely saturated with oil and coolant and not evident on the dipstick.

    Also, I found this piece of info on a site: "IT is very rare for a head gasket to leak engine coolant into the oil pan. The reason is because of the location of the oil return holes in the top of the block were the head bolts on are a long way from the water jacket holes."

    I say the leaky intake manifold gasket is common on these 350's

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    Re: 350 chevy coolant leak head gasket or intake

    I have the very relative 4.3 vortec that has a leaking intake gasket. You can smell it outside the vehicle easily, and see it leaking at the exterior front of the manifold. Could be possible, from what I hear... that they leak externally and internally.

    WAY too common on these GMs...
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    Re: 350 chevy coolant leak head gasket or intake

    its really common, the gaskets are plastic with rubber seals. after so many heatups and cool downs they crack and warp. when you do it, don't get oem ones, I did ones last week and they were metal with the rubber seals. much better design.

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    The moderately moderate moderator Turbo Mopar Staff black86glhs's Avatar
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    Re: 350 chevy coolant leak head gasket or intake

    Misunderstanding on the gaskets. The TBI engines use the regular flat gaskets. The 96 and later trucks(SCPI...sequential central port injection) used the Low Torque rubber and plastic gaskets.
    With that said, the TBI engines obviously can leak at the intake gaskets, just not as common as the newer.
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    Re: 350 chevy coolant leak head gasket or intake

    HIGHLY unlikely the intake gasket is causing your issue. Leaking intake gaskets won't cause the coolant to bubble and make the temp shoot up and its extremely rare they leak enough to turn the oil chocolate milk. You most likely have blown head gaskets. Also, those era blocks were nasty for cracking along the lifter galley, when you remove the intake, you'll see it under the head, aprox 3-6 inches long on one or both sides. We did a bunch of those under warranty.
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    Re: 350 chevy coolant leak head gasket or intake

    Quote Originally Posted by turbovanman View Post
    HIGHLY unlikely the intake gasket is causing your issue. Leaking intake gaskets won't cause the coolant to bubble and make the temp shoot up and its extremely rare they leak enough to turn the oil chocolate milk. You most likely have blown head gaskets. Also, those era blocks were nasty for cracking along the lifter galley, when you remove the intake, you'll see it under the head, aprox 3-6 inches long on one or both sides. We did a bunch of those under warranty.
    Yeah... he edited his post of the bubbles in the rad.... blown headgasket. While you got the heads off, at least you get to address the intake, too
    Quote Originally Posted by 22mopar
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    The moderately moderate moderator Turbo Mopar Staff black86glhs's Avatar
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    Re: 350 chevy coolant leak head gasket or intake

    +1 to the head gasket(s).
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  10. #10
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    Re: 350 chevy coolant leak head gasket or intake

    Well, he told me on the phone that he replaced the intake manifold gasket and now the temperature is back to normal. Hmmmm.... strange. Well apparently the owner is satisfied and took the truck back.

  11. #11
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    Re: 350 chevy coolant leak head gasket or intake

    I've seen plenty of these diagnosed as HG issue with an internally leaking intake gasket. usually in the higher mile motors the intake gaskets on the TBI cars eventually become an issue. I know of 4 such cases.
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