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  • Coolant leak, can't find it.

    My truck has been giving me the low coolant level light for the past few months. I checked it a few times when it first started but the level was always normal, so I figured it was just a bad sensor like my Camaro had a few years ago. Today I was under it changing the oil and noticed that it is leaking. I was under it about 8 days ago and there wasn't any noticeable leak. I have noticed that there was a small puddle under it the past few days but didn't think anything of it until I got under it to change the oil. It has not been overheating at all. The oil was normal color, dark brown to almost black. Here's a list of what I checked and seen/didn't see:

    Can't see any leak at all from looking into the engine bay from above.
    It's only on the passenger side.
    Can't really see where it is leaking from on the passenger from underneath.
    Nothing is wet from coolant on the front of the engine.

    Pics below:


    I poured some oil in a white plate to show the color to make sure there isn't any coolant in it. It looks white but that's the reflection of me taking the picture.



    From under the passenger side.



    Second picture from passenger side.

    Any suggestions? I found some different suggestions for what it could be from a google search, but I can't afford to be replacing stuff that isn't broke so I'd like to chase the problem down before I fix it.
    99 GMC Sierra Z71 NBS, ECSB, 5.3L V8, 4WD, Black, Toolbox, Fender Flares, Tint

  • #2
    Re: Coolant leak, can't find it.

    Hoses, radiator, water pump, heater core, intake gaskets, head gaskets, thermostat housing......... I guess you can skip the intake gasket since this is an LS engine.

    Get a flashlight and start looking all those things over after you've driven it.
    454cid
    1999 K3500 RCLB

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    • #3
      Re: Coolant leak, can't find it.

      My bet on the water pump.
      88 K1500 5.7 220K SOLD
      95 K2500 5.7 336k SOLD
      96 K2500 6.5 171K
      06 Trailblazer LTZ

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      • #4
        Re: Coolant leak, can't find it.

        Originally posted by FinalBreath View Post
        My bet on the water pump.
        Would a leak from the water pump make it to the back of the engine but not the front?
        99 GMC Sierra Z71 NBS, ECSB, 5.3L V8, 4WD, Black, Toolbox, Fender Flares, Tint

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        • #5
          Re: Coolant leak, can't find it.

          It could with the fan blowing it back.
          04 1500 Z71 6.0 LQ4 swap, BlackBear 06+ Grill/Hood, Vette servo, 3 BL,RC Keys, Truxedo, Bull Bar,KC, Cooper ST's Bilstein 5100's Tow's, Pypes M-80.


          1989 Silverado 2500 94+grill, Ram air hood, Mild built 355, Th400,

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          • #6
            Re: Coolant leak, can't find it.

            Originally posted by Craddock View Post
            Would a leak from the water pump make it to the back of the engine but not the front?
            Maybe, if it's dripping onto something else and traveling.
            454cid
            1999 K3500 RCLB

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            • #7
              Re: Coolant leak, can't find it.

              Originally posted by 454cid View Post
              Maybe, if it's dripping onto something else and traveling.
              Good point, I'll fill it back up with coolant and try to find it again.
              99 GMC Sierra Z71 NBS, ECSB, 5.3L V8, 4WD, Black, Toolbox, Fender Flares, Tint

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              • #8
                Re: Coolant leak, can't find it.

                look on the back left of the motor there is a quick disconnect for the heater core back there and the nipple coming out of intake tends to corroad or if youv'e bend the alum piping just a little the nipple will crack or break off all together found that out the hard way but its made of cheap potmetal and i got it out of the intake fairly easy with two hacksaw blade cuts, a screwdriver and a vaccum cleaner

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                • #9
                  Re: Coolant leak, can't find it.

                  Water pump gaskets. There notorious for leaking.
                  SOLD: 04 z71, 3200 circle D, longtubes, Corsa sport, TBG 4l60e, 93 BB tune, 4500K HIDS, and other aftermarket stuff.

                  Originally posted by 03SMURF
                  you have the meanest sounding 5.3 I have ever heard in person

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                  • #10
                    Re: Coolant leak, can't find it.

                    Popped open the hood again this morning to look at it again in the light. I have family in so I'm trying to juggle family and working on my truck. So when I got a better look at it in the light I can see some coolant has leaked from the top, I got some on my hand and it is definitely coolant. Picture below is where I can see it from the top. While I was looking at it I ran my hand across the back of the block from above where the heads and block meet to make sure that it wasn't the head gasket leaking from there. It was dry, just dust on my hand.



                    Does this look like a leaking gasket or messed up water pump? This is right below the throttle body on the passenger side. I can see how the fan would blow the coolant toward the back like someone mentioned above. This is about the only thing I more trouble seeing on my truck motor compared to my lt1 in my old Camaro.
                    Last edited by Craddock; 11-06-2011, 10:05 AM.
                    99 GMC Sierra Z71 NBS, ECSB, 5.3L V8, 4WD, Black, Toolbox, Fender Flares, Tint

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                    • #11
                      Re: Coolant leak, can't find it.

                      The pump may be OK, you will have to access the weep hole to see if the internal seals have began to leak. The weep hole is on the bottom of the snout of the water pump. I would almost bet though that its just the gaskets.

                      And furthermore you more than likely have been loosing coolant for a while. Most gaskets just seep enough that you cant find the leak.
                      SOLD: 04 z71, 3200 circle D, longtubes, Corsa sport, TBG 4l60e, 93 BB tune, 4500K HIDS, and other aftermarket stuff.

                      Originally posted by 03SMURF
                      you have the meanest sounding 5.3 I have ever heard in person

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                      • #12
                        Re: Coolant leak, can't find it.

                        I just went to check the weep hole and nothing directly under the center of the pump is wet, only on the passenger side. None of the other pulleys or the belt is wet and it doesn't have the dried coolant look on the belt like my Camaro had when the pump go bad. I also took a dry clean shop towel and rubbed the underside of the water pump as much as I could reach with no coolant, even tied it to a screwdriver to extend my reach and nothing on it. So I'm looking at replacing both of them just for safety because it has 135xxx miles on it and as far as I know it has the original water pump. I will be filling it up, drying everything that I can off and seeing where it leaks again just to make sure.

                        Thanks to everyone who has offered advice so far, and any more will be appreciated.
                        99 GMC Sierra Z71 NBS, ECSB, 5.3L V8, 4WD, Black, Toolbox, Fender Flares, Tint

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                        • #13
                          Re: Coolant leak, can't find it.

                          I would check the coolant lines going to the throttle body. They are right above that spot in the picture. If you can get your hands on a radiator pressure tester and pump up the system the leak should be very evident.
                          2004 Suburban 2500 Quadrasteer 4WD 6.0L
                          1985 Silverado C-10 RCSB 2WD 5.7L
                          1992 Sierra 1500 2WD 5.7L
                          2000 Tahoe Limited
                          1999 Tahoe Limited

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                          • #14
                            Re: Coolant leak, can't find it.

                            Originally posted by kemble View Post
                            .....There notorious for leaking.
                            They are? I don't have any experience with an LS engine....... what makes them prone to leaking?
                            454cid
                            1999 K3500 RCLB

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                            • #15
                              Re: Coolant leak, can't find it.

                              Originally posted by 454cid View Post
                              They are? I don't have any experience with an LS engine....... what makes them prone to leaking?
                              I'm not quite sure really, maybe the construction and initial torque from factory?
                              SOLD: 04 z71, 3200 circle D, longtubes, Corsa sport, TBG 4l60e, 93 BB tune, 4500K HIDS, and other aftermarket stuff.

                              Originally posted by 03SMURF
                              you have the meanest sounding 5.3 I have ever heard in person

                              Comment

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