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1991 5.7 Cooling system refill

Old June 23rd, 2019, 2:02 PM
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Default 1991 5.7 Cooling system refill

I just flushed out all the old coolant liquid by removing the plug on the radiator and the plug on the bottom of the engine on the driver side. I also replaced the thermostat for a new 1. But when i refill it after about 1,5 to 2 gallons of coolant it wont fill anymore. Am i missing something? Because i drained more than that. I started the truck and it lowered a bit and got up to heat so the thermostat went open but still i cant fill it up anymore because it will overflow then. It can idle for a long time and stays at normal operating temps.

Is there maybe an air bubble? And maybe anybody got some tricks or tips or a guide wich explains it step by step so i can check if i missed something? Or maybe you guys got some tips for me?

What i also found strange is that i got the official maintenaince books that GM gave to their mechanics but there is no indication of how much fluid there actualy is in the system? I found some things online after a few google searches that say its about 17 quarters of liquid in the system.

Thanks in advance!
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Old June 23rd, 2019, 4:42 PM
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Bleed the system, If there is not a bleed valve off the top radiator hose on the intake manifold, bleed the system (with it running, and warmed) loosen the top radiator hose clamp to let the air out.
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Old June 23rd, 2019, 5:17 PM
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with the block completely emptied i would fill first through the coolant housing, then install the housing and top the system off. on my cummins along with other engines ive filled the system as far as i could then pump the upper hose in an attempt to push the coolant into the top of the block.
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Old June 23rd, 2019, 7:49 PM
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Yes, Maikelo, probably air high in the engine. Some tricks people use are to park with it facing uphill, radiator cap removed, then let it run and hopefully push the air out when the thermostat opens and the coolant begins moving through the engine, or much simpler, remove one of the hoses to the heater core and add coolant through there. Both of these methods will cause spilling if you are not very careful to catch it. If your truck still has the overflow tube and tank in place, the official method is to simply start it and bring it up to temperature, then turn it off to cool down, and repeat 4 or 5 times. Each time it heats up, it forces a little air into the overflow tank, and as it cools down, liquid is drawn back into the radiator to replace that volume of air. Do that enough and most if not all of the air is removed. You might need to add coolant to the overflow tank if it draws it all back into the engine. If there is a leak somewhere, this will not work.

The owner's manual for my 1997 5.7 C1500 says 17.5 quarts coolant capacity. Mine does not have the trailer towing package option.
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Old June 23rd, 2019, 8:36 PM
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I've seen people use this kit for bleeding the system. I bought one from another manufacturer, but haven't used it yet. My 1994 owner's manual says for the 5.7L it's 17.5 quarts without ac, 18 quarts with ac.

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Old June 24th, 2019, 11:58 AM
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Thanks for the reply's.

Its indeed 18 quarts with ac, appareantly it does show in the glove box manual.

Im gonna try a vacuum tool made for filling cooling systems, it should suck out the bubble easy. Also a handy tool to have if it works ofcourse..
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Old June 28th, 2019, 8:39 AM
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I still dont really understand what is happening.

I let all the coolant out of the system by opening the bolt with the butterfly wings on the radiator. After that I can only fill just about 3 gallons of new coolant.

What am I missing because it should be 17 to 18 quarts? I used a vacuum on it and still the same... Put it on an angle because of air buble but still the same.

engine temp is also at normal operating temp when I let it warm up. Thermostat also works normal.

Last edited by Maikelo; June 28th, 2019 at 9:06 AM.
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Old June 28th, 2019, 1:46 PM
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well 3 gallons equals 15 quarts, so youre only missing 2-3 qts if thats the right measurement. could be just stuck on the engine or heater core
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Old June 29th, 2019, 12:51 PM
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Yes, maybe the engine block is not drained completely, or maybe the 18 quart value also includes the coolant in the separate overflow reservoir.
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Old June 29th, 2019, 12:56 PM
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Originally Posted by Irish_alley View Post
well 3 gallons equals 15 quarts, so youre only missing 2-3 qts if thats the right measurement. could be just stuck on the engine or heater core
Wait a second! 3 gallons is 12 quarts. "Quart" = one quarter of a gallon (1/4)

U.S. quart is 32 ounces(fluid). U.S. gallon = 3.78541 liters
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