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Mysterious Coolant Leak

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Cal_truck22, Feb 2, 2008.

  1. Cal_truck22

    Cal_truck22 New Member

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    Hopefully someone can help me out. I have a 2000 Silverado with the 5.3L engine. Recently, I have been losing coolant at a slow rate. I have had the cooling system pressure tested by a dealer and an independent mechanic and both say that there is not a pressure leak in the system. I have checked the oil and I do not see any indication of antifreeze in the oil, so I do not suspect a head gasket problem.

    Also, there is no visible signs of coolant leaking from the system (I see no coolant on the ground under the car and the engine compartment does not smell of coolant). So, if the pressure is good and the head gasket appears not to be the problem, where is the coolant going? I have changed the radiator cap on the surge tank, but this did not appear to help. Has anyone else seen a problem like this? I am going crazy (not to mention spending a lot of money doing pressure tests!) with this problem.

    Anything will heip. Thanks!
    Last edited by a moderator: Feb 8, 2008
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  2. 84fiero123

    84fiero123 New Member

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    First welcome aboard. [​IMG]

    If you don’t have a pressure leak in the system I really don’t think you have anything to worry about.

    But if you start loosing more coolant, more quickly I would have the test done again and this time with a die that will show up under a light. It just makes it easier to see where the leak is coming from.
    #2
  3. Cal_truck22

    Cal_truck22 New Member

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    Thanks

    84fiero123, first thanks for the warm welcome. Second, thanks for the truck advice. Right now, the temp does not budge from the normal temp, so it appears it is not a big deal. It is just inconvient to fill the surge tank with 1Q of antifreeze every 1.5 months or so. Hopefully it does not get worse.
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  4. tbplus10

    tbplus10 Moderator

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    Check the surge tank and connecting hose, this is the only part of the cooling system that isnt pressurized and wont show a leak when you do pressurize the system.
    Almost all surge tanks are plastic and they break down from the heat after a while.
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  5. Duramax04

    Duramax04 New Member

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    I have a mystery machine like that also.My old 97 Z-71 is losing antifreeze but i can smell it when it is setting still at an idle but there is never any signs of a leak. I can park it on the concrete or in the garage and let it set overnight and everthing is dry the next morning. I probably add a quart every couple of months.I have a pressure tester, guess i should put it to use,huh? Just might do that today.
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  6. Cal_truck22

    Cal_truck22 New Member

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    Duramax04-
    Let me know what you determine from your pressure test. If your problem is anything like mine, the pressure test will come out fine, and the mystery will continue.
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  7. Duramax04

    Duramax04 New Member

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    Cal, your exactly right. Pressure test was good and cap checked out okay. Back to scratching my head.
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  8. JayMack75

    JayMack75 Former Member

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    I had a similar problem on my old silverado. The source of my problem was at the back of the intake. When the engine was warm it would leak, but would burn off before anything touched the ground. When it was cool, nothing leaked at all. It was a pesky problem and I sold the truck (unfortunately) before I was able to fix it.
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  9. Cal_truck22

    Cal_truck22 New Member

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    JayMack75-
    How did you determine that the intake gaskets were the problem? After I drive the truck for a while, I lift the hood and try to smell any coolant in the engine compartment. However, I smell nothing. If it is only leaking when driving, would I be able to smell coolant in the engine compartment? The problem in my truck is starting to get a little worse, so I am getting more concerned about the problem. Thanks.
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  10. mack1611

    mack1611 New Member

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    Cal,
    Have you located your mystery leak?
    I'm having the same problem on my 2001 c1500. No visiable leak but I need to add a quart of coolent about once a month.
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  11. Cal_truck22

    Cal_truck22 New Member

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    Mack1611-

    I have not yet located the source of my coolant leak. I took the truck to the dealer where they hooked it up to the pressure tester overnight. No loss of pressure (within reason of the tester) overnight. Dealer also told me that on the 5.3L engines, unlike the 5.7L, the intake manifold is dry. Thus, the source of the leak could not be the intake gasket. Dealer is confused by the problem too. His assement of the situation is that the coolant can only go to one of three places: the crackcase, out the tailpipe, or leak from the coolant system. There is no coolant in the oil, so there goes the "in the crackcase" theory. The plugs are not fowled and no misfire, so there goes out the tailpipe. No pressure loss in the coolant system, so there goes leak in the coolant system. Also, as far as the coolant system, there is no signs of leaks anywhere in the engine compartment or on the engine itself. So, the mystery continues.
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  12. larryderouin

    larryderouin New Member

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    I had one of those on my G20 back in 90. Leak down almost a whole bottle in a week. No stains, no visible signs of leakage.

    Turns out there was a small crack in the block in the lifter valley that would weep when the engine warmed up and would cclose when cool. between #3 & #5 cylinders. Pressure tests were good. As it was under warranty they replaced the short block.

    Don't discount a small crack in either one of the heads, or in the block. Not all cracks in the block will drain to the crankcase and mix with the oil. Mine was just enough to lose coolant but slow enough to burn off as soon as it leaked out.

    This was on a '89 G-20 van with a 305.

    Larry
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  13. jdchet

    jdchet New Member

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    Have you checked to see if there is excessive pressure in the cooling system? Do you have good heat? Oops...So Cal.....no heat needed! JK:lol: If your getting slight combustion pressure in cooling system heat won't work too good if at all! Might have slight leak in Head gasket in the combustion chamber.
    Just thinking out loud!!!!!:confused:

    JD:rules:
    #13
  14. Cal_truck22

    Cal_truck22 New Member

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    Thanks everyone for the insight. Heat in the truck is good. Been cool the last few mornings and I have had to use the heat. It heats up real fast and I do not have a problem in this regard. As far as the head leak, I hope this is not the problem. If it is a head leak, I think the Pacific Ocean will soon have a new artifical reef!
    #14
  15. smokesierra

    smokesierra New Member

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    Im having a similar issue with my 03 sierra 5.3. but i do get a visible sign of leak, i get a small puddle every few days, and im suspecting a bad water pump or gasket, but i will know for sure after the mechanic looks at it.
    #15
  16. brooklyn718

    brooklyn718 New Member

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    okay i got a 1999 yukon gmc , i had a leak in my heater control valve, i changed it my self, after 2 days everything was going fine until the other day i notice leak again and the smell of coolant, i checked under the hood and there was nothing leaking from the hose, the leak was coming from under the truck right before the transmission. it was coolant. even when the ruck is parked it leaks a little, what can this be? i just had a head gasket changed last month, can this be the result. please help me.
    Last edited: Apr 14, 2008
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  17. woodwerkstudio

    woodwerkstudio New Member

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    I have a 2004 Silverado Z71 and it eats about 1/2 gallon of coolant every 2 weeks. It has been presure tested by the dealer I started to go to. Its a great truck but I have started to have this problem within the last month. So I asked a friend who runs at a Porsce dealer what the problem could be. He subscribes to alldatapro.com and there seems to be a porosity crack in a very specific area of the cylinder head(s) produced with the "Castech" logo on them. GUESS WHAT KIDDIES. THAT IS THE PROBLEM. MY TRUCK IS IN RIGHT NOW AS WE SPEAK. THANK GOODNESS I HAVE an extended warranty. They are replacing the block, rods, lifters etc...... All were corroded by the leak. Get the alldatapro printout and bring it to the dealer. Although I don't know about GM going belly up . Good luck!!
    Last edited: Dec 8, 2008
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  18. terry16120

    terry16120 New Member

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    i have a 2000 silverado with the 5.3 and have had the same problem since i bought it about every month, month and a half i have to fill the over flow resorvoir i how ever did have a small leak where the water pump meets the block but it was so small it didnt show up overnight only while it was running did i notice a small drip that was green. after i replaced the waer pump i had a new problem i had a little leak that took a long time to discover in those damn plastic connetions for the heater core in fact i didnt figure this out till it finally fell to pieces. all that is fixed but im still having to fill the reservoir every 3 to 4 months dont know where the water is going though.
    #18
  19. brooklyn718

    brooklyn718 New Member

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    i had my water pump changed last month, then my heater control valave, now i don't know where this new leak is coming from. it is underneath the passenger side of the truck. should i take it back to the dealer that did my head gasket and my water pump. they might tell me something different. even when the truck is off there is a small puddle.
    #19
  20. texaschevy03

    texaschevy03 New Member

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    Heater not working, and low coolant level

    I am having the same problem on my 03 Chevy Silverado 5.3L. My heater seems to have gone out and my coolant resevoir has to be filled up at least once a month. I find no signs of a leak. I figured maybe it was around the bottom hose on the resevoir. Running or not nothing showing on ground in the form of antifreeze.
    #20

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