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Possible head gasket symptoms.

In my 1994 GMC Sonoma SLS vin: Z truck, I am slowly loosing coolant. I don't see any leaks though. Is it possible to have a blown head gasket, yet not loose any compression, and not get any coolant in your oil, and not blow any smoke/have a funny smell. Because I have no idea where it could be happening.

PS: I just replaced the thermostat, both hoses, and flushed the whole system.

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To find out for certain if you have a head gasket problem do a leakdown test this video shows an excelent video for this

Some other things to look for that may cause the the lose of fluids , check the heater core inside the car . look for a wet floor on the passenger side , look for steel coolant lines that may be full of small pinholes from rust . they will release coolant as steam and you wont see any sign of the lose. you can also check for heater hose pinhole that could be dripping directly onto the exhaust and therefore no sign of lose ans it is turned to steam . Check the system cold with pressure . Look at the seams on the rad for moisture . Then run the system up to op temp shut the truck down and then pump up the pressure . This is done with a pressure test pump . Check your PCV valve is working properly . Check the intake manifold for leaks this usually happens in the intake valley under the throttle body . Just some ideas Hope they help

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Holy $@$* man thanks! That is an awsome test for especially my engine to see how good the rings and valves still are. 130k miles can do a lot to an engine!


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@parzival possible but unlikely. You would see at least one of the symptoms you described. Check your cooling system and preform a pressure check on it. See if there is a leak somewhere. Let us know what year,make and model your truck is.

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1994 GMC Sonoma SLS vin: Z because for some reason they had to rebuild the cooling system after the W models came out. XD


Hi ,

I agree with @oldturkey03 get a pressure test done. You may have a faulty radiator pressure cap or a leak in the radiator core or a heater hose which only shows under pressure.

I know that you said that you don't see any leaks but have you checked for coolant "stains" on radiator, the engine block, heater hoses etc

Also have you checked inside the cabin under the dash? You may have a leak in the heater radiator. Try leaving the heater temperature control set to OFF (or cold) if it not there already, as this will prevent coolant flowing into and through the heater and see if you still lose coolant.


Thanks jey, and I agree. I will do a pressure test with smoke as well. I know for a fact its not the heater coil because just recently I used the heater and there is no fluid on the floor. And if it makes any difference, this leak seems to only happen during normal operation at temp. If that adds any obvious area to check.


I figured it out! Turns out, after I flushed the system, there must have been some places that didn't have coolant in it, so when it ran, it drained the tank. After refilling the tank, it has stayed at a constant level. But thanks guys! I will definitely remember and even do a leak down to test out how good that old engine still is.


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Kevin sera éternellement reconnaissant.
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