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  • Antifreeze Leaking Up Through Intake Manifold Bolts?

    1990 K1500 5.7L TBI. 165k miles.

    When I was replacing my distributor last week, I saw a few small pools of antifreeze laying on top of the manifold. My mechanic was the local head guy at the Chevy dealership for 30 years. He took a look at it and said it was probably leaking up through the bolts.

    He told me to take them out one at a time, clean them off with a wire wheel, and goop silicone paste or RTV on the threads, and reinstall each bolt. Torque them down to about 25 ft/lbs.

    What do you guys think? He says the sealant is known to fail and he's done this to dozens and dozens of trucks like mine. He says the intake manifold gasket probably does NOT need replaced. But that's what usually gets done to fix the problem.

    He wanted $300 to replace the gasket, put new coolant in it, and change the oil. Told me to try the bolt trick first on my own.

    Just looking for some advice. Has anyone had a leak like this and fixed it by cleaning up the intake bolts?

    Thanks in advance.
    Blue on Black -- 1990 K1500 350TBI, 175k.

  • #2
    Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

    try it or cough up 300 bucks.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)

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    • #3
      Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

      yea id give it a shot and if it doesnt work then have him replace the gasket, sounds like hes trying to help u out and save u some money


      1994 Suburban K2500, 6.5 turbo diesel, 4.10s, 14bff, 4l80e, g80
      2010 Toyota Carolla S (DD)
      2000 Ford F250 V10, 4x4
      1995 Chevy Suburban K1500, 350 TBI, g80 (sold)
      1992 Suburban k2500, 454 TBI, g80 14 bolt FF, 4l80e(sold)

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      • #4
        Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

        I know this.....I was hoping to hear from someone that had antifreeze laying on top of their intake and they fixed it by cleaning up the bolts, gooping them up with RTV, and torquing them back down.

        Anyone out there ever do this and it worked? Or does everyone usually get have their gasket replaced....which would include the above mentioned tasks.....and presto....their leak was fixed. You'd never know if it was a gasket or the bolts.

        Anyone tried this shortcut and have it worked out for them?
        Blue on Black -- 1990 K1500 350TBI, 175k.

        Comment


        • #5
          Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

          You're at the mileage where intake gasket failure isn't unheard of. Try these, about 160K miles:



          Now here's the key information, please pay close attention. NONE of the intake bolts on your TBI small block engine pass through into a cooling passage. NONE. No matter what anybody tries to tell you. The bolt that is at each corner of the intake goes into a blind hole. The other 8 go into holes that are open into the lifter valley*; the only thing that can travel up those bolts is oil, and this frequently happens on the 4 center-most bolts. A minor annoyance, not a serious issue.

          If you've got puddles of coolant on your intake around the bolts, you almost surely have failed intake gaskets, or a leak from outside that is pooling on the intake, like a failed heater hose quick connect fitting - this is at the passenger rear of the intake.

          Gooping some sealant on the bolts and putting them back in might band-aid the issue so you're not getting the visible evidence, but that doesn't mean you've actually fixed anything - they're still possibly leaking, just not where you can see it. If they're leaking internally as well, continuing to drive it will end up very bad for you when the coolant gets into the oil and destroys your bearings.

          *I can gladly post pictures that prove this for anybody that would like to debate it.

          Richard

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          • #6
            Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

            What he said ^.

            One more thing, putting RTV or silicone grease to use a sealant, is DUMB. Use proper thread sealer. Not that it applies here, but I had to mention it.

            87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

            07 GMC Sierra Classic - 2" Rough Country Full Leveling Kit/285 Duratracs/Gibson Exhaust/10% Tint/Billet Grille

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            • #7
              Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

              Absolutely what the guy two posts above me said. I am in the process of replacing my intake manifold gaskets on my '92. I had oil pooling up on the manifold from those bolts, which is what is to be expected when the sealant fails. BUT if you have coolant pooling up, that definitely means gasket failure IF the bolts are where they are coming from. Check your heater hose connection while its running, see if it will blow bubbles in soapy water right when you start it up.

              The intake manifold gasket job isn't that hard, but if your local guy said $300, heck that's almost worth it if you are time strapped. Lowest I found local was $650, so I am doing mine only spending an hour a day when the weather is good, which it hasn't been lately.

              Go EASY on the RTV if you do it. A thin bead around both sides of the port heads on the gaskets and a medium thick bead on the ends of the block is all you need. I am still scraping off the 800 gallons of RTV the PO used when he replaced the gaskets in mine some time ago!

              Also, go for a thread sealant instead of RTV on the bolts. The threads can push RTV out, but thread sealant is made to slip by the threads of the hole before it dries.
              1992 ECSB 5.7L Z-71

              Past GM's:
              1998 ECSB 5.7L Z-71
              2007 Tahoe LT2 5.3L
              1999 ECSB 5.3L Z-71
              1992 RCSB 5.7L Z-71
              1993 RCSB 5.7L Z-71

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              • #8
                Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                Oh, one other thing, please don't just pull the bolts and put sealant on them! Atleast right now some of your leaking coolant isn't going into the block!
                1992 ECSB 5.7L Z-71

                Past GM's:
                1998 ECSB 5.7L Z-71
                2007 Tahoe LT2 5.3L
                1999 ECSB 5.3L Z-71
                1992 RCSB 5.7L Z-71
                1993 RCSB 5.7L Z-71

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                • #9
                  Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                  My first guess is a Thermostat housing gasket where the upper rad hose mounts to the block, or the hose could be cracked where it tightens on. Check that first. They leak sometimes and puddle onto the intake.

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                  • #10
                    Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                    So I thoroughly cleaned and dried the top of the intake manifold.....started up the truck and watched and waited.....and it's real clear that the antifreeze leaking from the intake gasket. Here is what I think is strange: both side are leaking right up at the front corners. Each front corner has bolts that have ground wires attached to them.

                    From what you guys have seen and know......is having both sides leak common? The front of the manifold is obviously leaking oil as there is crude around the water pump.....but I guess what I'm asking is: Is both front sides leaking telling me anything else? For instance, the manifold is probably warped? This truck has obviously been over heated? Something like that....

                    I just didn't know if both sides leaking was pointing to other problems or not.

                    Thanks in advance.
                    Blue on Black -- 1990 K1500 350TBI, 175k.

                    Comment


                    • #11
                      Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                      I see antifreeze on the pass. side of my intake manifold. 1991 4.3L. I am gonna check it out like you guys advised. Great information. Thanks
                      Pete

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                      • #12
                        Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                        Originally posted by Phishin View Post
                        So I thoroughly cleaned and dried the top of the intake manifold.....started up the truck and watched and waited.....and it's real clear that the antifreeze leaking from the intake gasket. Here is what I think is strange: both side are leaking right up at the front corners. Each front corner has bolts that have ground wires attached to them.

                        From what you guys have seen and know......is having both sides leak common? The front of the manifold is obviously leaking oil as there is crude around the water pump.....but I guess what I'm asking is: Is both front sides leaking telling me anything else? For instance, the manifold is probably warped? This truck has obviously been over heated? Something like that....

                        I just didn't know if both sides leaking was pointing to other problems or not.

                        Thanks in advance.
                        The fronts fail more often than the rears, because the rears don't flow as much coolant - they have restrictors back there with tiny little holes for the coolant. When I pulled mine apart, only the driver's side had failed (at the front), but the passenger side front was ready to go at any moment. The picture I posted earlier is the driver's side; here's my passenger side:



                        Your truck? Almost surely time for intake gaskets...

                        Richard

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                        • #13
                          Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                          3 bills is a good price to farm it out. My '94 passenger side front bolt had a small coolant leak, applied thread sealant, stopped it. I've had oil leak out the back of the manifold and coolant on the 2 front sides like yours. While the intake is off, notice carbon build up under EGR valve, clean as necessary.

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                          • #14
                            Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                            For the record I think the Vortec 350's have bolts that go down into the coolant passage. Perhaps that's what your mechanic was thinking about.
                            '97 Sierra ECSB 4x4 5.7
                            Just trying to postpone the inevitables of living in the rust belt...

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                            • #15
                              Re: Antifreeze Leaking Up Through Intake Manifold Bolts?

                              If a mechanic can't tell the difference between a TBI and Vortec 5.7, and makes a recommendation like that without being informed, he's not a mechanic. He's a hack. In either case the intake gaskets need to be replaced, especially on the Vortec engines, which are way, way, way more prone to leaking the coolant into the oil = destroyed engine. Genius-level advice: just pull the bolts out and pooky them. Yeah!

                              Richard

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