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Coolant leak, can't find it.

This is a discussion on Coolant leak, can't find it. within the Technical / Maintenance forums, part of the General Discussion category; My truck has been giving me the low coolant level light for the past few months. I checked it a ...

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    Coolant leak, can't find it.


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    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

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    Registered User 454cid's Avatar
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    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.
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    G-FORCE FinalBreath's Avatar
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    Re: Coolant leak, can't find it.

    My bet on the water pump.
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    Re: Coolant leak, can't find it.

    Quote 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?
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    Registered User Blue 04 Z71's Avatar
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    Re: Coolant leak, can't find it.

    It could with the fan blowing it back.
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    Registered User 454cid's Avatar
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    Re: Coolant leak, can't find it.

    Quote 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.
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    Re: Coolant leak, can't find it.

    Quote 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.
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    Registered User tahoe 9955's Avatar
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    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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    NO ROOF RACK NEEDED kemble's Avatar
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    Re: Coolant leak, can't find it.

    Water pump gaskets. There notorious for leaking.
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    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 at 10:05 AM.
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    NO ROOF RACK NEEDED kemble's Avatar
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    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.
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    Quote Originally Posted by 03SMURF View Post
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    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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    Registered User Mr_Shamrock's Avatar
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    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.
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    Registered User 454cid's Avatar
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    Re: Coolant leak, can't find it.

    Quote 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
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    NO ROOF RACK NEEDED kemble's Avatar
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    Re: Coolant leak, can't find it.

    Quote 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?
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    Quote Originally Posted by 03SMURF View Post
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    Re: Coolant leak, can't find it.

    Went to the store today after my family left (in my gf's car) and got a gallon of premixed coolant and it took the whole gallon to just barely fill it above the plastic "x" inside the coolant tank in the engine bay. I poured it in as the engine was warming up and let it get to regular running temp for a few minutes before I shut it off. When I shut it off I dried the spot from my pictures above. After about 10 seconds it looked exactly the same. The picture below is from after I dried it a few times, same thing, it filled right back up.



    So am I looking at a cracked head?
    99 GMC Sierra Z71 NBS, ECSB, 5.3L V8, 4WD, Black, Toolbox, Fender Flares, Tint

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    Re: Coolant leak, can't find it.

    Have you looked at the coolant line to tb. That was my first guess.

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    Re: Coolant leak, can't find it.

    I'd suggest stopping by a shop with a pressure tester and having them diagnose it for you. Will cost some $$ but in the end at least you'll know what you end replacing actually is the problem if you can't seem to find it by looking around.
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