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Thread: Losing coolant no visible leaks Off Topic J-Body problem

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    Default Losing coolant no visible leaks Off Topic J-Body problem

    I've got a J-Body question, but that forum has turned into a desert, so I was hoping some of the vast mechanical knowledge available here could help me. My 2002 Ecotec Sunfire with 200k is losing a small amount of coolant based on my having to top off an inch or two in the reservoir/surge tank(this model doesn't have a radiator cap) every other week, but I can't find any sign of a leak. I left it idling for an hour with a sheet of cardboard underneath and nothing. I left the sheet there overnight, and nothing. Hose attachments are all tight and the engine is bone dry. No overheating issues and no suspicious exhaust. It runs perfectly fine.
    Today I rented a cooling system pressure tester and my system won't hold pressure at all. Once I pressurize to 15 psi, the needle slowly begins falling and in a couple of minutes all pressure is gone. I couldn't see or hear any escaping fluid during the test. The bottom of my engine is bone dry, as is the radiator, all the hoses, and the connections on the pipe that goes from the thermostat to the back of the water pump. I don't smell or see coolant in the passenger compartment, and I pulled a cold oil sample from the drain plug and the oil looks perfectly normal.
    I'm totally stymied.
    Any ideas?
    Thanks.



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    Senior Member CorvairGeek's Avatar
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    Pull the spark plugs and look for the abnormally clean one. Everything will be very clean if a cylinder is consuming anti-freeze. Which engine are with dealing with, the push rod 2200 that is notorious for leaking coolant (externally) between the head and block or the OHC engine which can have tricky leaks (possibly concealed) around the water pump?
    Jerry

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    It's the DOHC ecotec with the chain driven water pump.
    Would I not be getting white exhaust if I was burning coolant?

    Thanks.

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    I pulled the plugs and they all look clean and approximately the same. This car gets almost entirely highway miles.

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    Senior Member CorvairGeek's Avatar
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    Quote Originally Posted by Sigurd Jarlson View Post
    I pulled the plugs and they all look clean and approximately the same. This car gets almost entirely highway miles.
    I thought maybe you were catching it early so that the exhaust vapor may not be prominent yet. If the plugs all look the same, I would guess it it not going through a cylinder.
    My next thought is that it is evaporating off a hot surface (radiator or heater core - having too many of these myself, sometimes on the floor board, sometimes not).
    These engines can leak coolant internally from the water pump, IIRC. I would think you would be detecting it visually, without oil analysis, if this was the case.
    Jerry

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    Quote Originally Posted by CorvairGeek View Post
    I thought maybe you were catching it early so that the exhaust vapor may not be prominent yet. If the plugs all look the same, I would guess it it not going through a cylinder.
    My next thought is that it is evaporating off a hot surface (radiator or heater core - having too many of these myself, sometimes on the floor board, sometimes not).
    These engines can leak coolant internally from the water pump, IIRC. I would think you would be detecting it visually, without oil analysis, if this was the case.
    The heater core is such a bear on these cars, that I wouldn't even attempt it unless I was positive that was the cause. I thought maybe I heard almost undetectable hissing from the actual surge tank itself when it was pressurized, so I ordered a new one. If I swap it out and it doesn't hold pressure, at least with a new one I'll actually be able to see the coolant level, since the original one is such a cloudy plastic.

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    Senior Member CorvairGeek's Avatar
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    Sounds like a good plan. I forget about those, as we have 5 antiques all with old fashioned radiator caps on the radiator.
    Jerry

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    The plastic radiator cap can also be the culprit. The tank may have a pinhole leak in the top, and only be leaking vapor and pressure. With your pressure tester, get it pressured up, and spray it down with some really soapy water.

    The cap on the tank is also a known culprit, again only releasing vapor and pressure, it may act like its tight and sealed, but is slowly leaking.
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    Quote Originally Posted by Pontiac6ksteawd View Post
    The plastic radiator cap can also be the culprit. The tank may have a pinhole leak in the top, and only be leaking vapor and pressure. With your pressure tester, get it pressured up, and spray it down with some really soapy water.

    The cap on the tank is also a known culprit, again only releasing vapor and pressure, it may act like its tight and sealed, but is slowly leaking.
    The first thing I did is change out the cap, but it didn't seem to help. I also tried the soapy water on the tank, but found nothing definitive. I'm hoping just changing it out helps. Thanks.

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    Senior Member Keiths1976's Avatar
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    Honestly best advice grab some dye and drop it in the coolant and get a black light from the aquarium store or what ever place carries them . At least at night you should find residue . Some gm cars use the ac coolant drip hose as the heater core as well if carpet is not wet or anything the dye will help you sing those roots .

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    Crap I?m sorry ..... * Find those leaks ...My bad spell check didn?t pick that one up lol

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