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  1. #11



    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.

  2. #12
    Jr. Apprentice
    Join Date
    Jun 2005
    East Coast


    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.


  3. #13
    Sr. Apprentice jdchet's Avatar
    Join Date
    Oct 2007
    Lake Peekskill, New York, United States


    Have you checked to see if there is excessive pressure in the cooling system? Do you have good heat? Oops...So heat needed! JK 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!!!!!


    [B][I][SIZE="2"]2007 Silverado LT 4wd ext cab 6.6' box,4.8l V8.
    2007 Equinox AWD SUV

  4. #14


    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!

  5. #15


    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.
    2003 GMC Sierra 1500 5.3 ltr.

  6. #16


    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 by brooklyn718; 04-14-2008 at 11:02 AM.

  7. #17


    Quote Originally Posted by Cal_truck22 View Post
    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!
    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 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 by woodwerkstudio; 12-08-2008 at 03:00 AM. Reason: Updating original post

  8. #18


    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.
    2000 silverado lt ext. cab 5.3

  9. #19


    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.

  10. #20

    Default 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.

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