Flushing a gunked up coolant system. Suggestions?
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Instructor
Joined: May 2021
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Flushing a gunked up coolant system. Suggestions?
I have a c5 with a la364. I pulled a big stupid and mixed the coolant in it with a universal. It worked for a while then it started overheating. I got pink yogurt all in it. I'm guessing it clogged the thermostat and possibly other things. I be wanted to yank the thermostat and run it with cleaner and water multiple times until clean but I can't go with no thermostat. I put the cleaner in the resivor and tried but no luck. I was going to dump it in the radiator directly and try that. If the gunk freezes the thermostat I get no circulation and the cleaner can't do it's job. Yes...I know I'm stupid for mixing. Any suggestions for flushing? I can't drive it because it overheats as of now so I'm trying parking lot tactics. Thanks.
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The way it looked to me the thermostat is all one unit that bolts directly to the block. If I don't have a thermostat I just have a hose and no way to connect... I've had other vehicles that you can remove thermostat and bold back in but the thermostat I have is all one unit. Unless you know something I don't? I didn't see a way of removing the thermostat from the housing but it was all covered..
Drifting
Joined: Jan 2014
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From: Cincinnati OH
I understand that the original C5 thermostats were one piece but the water pump was upgraded later by GM and required a different 2 piece thermostats. Looks you've got the original design and pump. If you could get a replacement 1 piece thermostats, you could the butcher the old thermostat to force it open and reinstall. Not a good solution - perhaps someone will suggest a better option short of removing the radiator and having it flushed. You might try calling a radiator shop and see what they suggest.
Thread Starter
Instructor
Joined: May 2021
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I understand that the original C5 thermostats were one piece but the water pump was upgraded later by GM and required a different 2 piece thermostats. Looks you've got the original design and pump. If you could get a replacement 1 piece thermostats, you could the butcher the old thermostat to force it open and reinstall. Not a good solution - perhaps someone will suggest a better option short of removing the radiator and having it flushed. You might try calling a radiator shop and see what they suggest.
Drifting
Joined: Jan 2014
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From: Cincinnati OH
Last edited by hdrider1; Nov 23, 2025 at 07:21 PM.
Thread Starter
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That is the exact one I just bought. When I stuck it in and ran the car out started to overheat so I stopped and pulled it out. It was covered in pink yogurt. I went to the gas station next door and cleaned it up. Then I put flush in it and ran it for a little while. By then it was dark and I had to quit.
Drifting
Joined: Jan 2014
Posts: 1,623
Likes: 1,134
From: Cincinnati OH
That is the exact one I just bought. When I stuck it in and ran the car out started to overheat so I stopped and pulled it out. It was covered in pink yogurt. I went to the gas station next door and cleaned it up. Then I put flush in it and ran it for a little while. By then it was dark and I had to quit.
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Thread Starter
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So I did exactly what we discussed. I'm still flushing and got good results and bad. Still overheats. I sprayed water in the main hose and it cycles all the way around back to thermostat. So no fully clogged there. Turned heat on full. Blows cool. ... I'm really leaning to bad water pump but I can't understand why the resivoir is still boiling if there is 0 circulation.
Race Director
Joined: Oct 2004
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If your system clogged as badly as you say, I believe your radiator and heater core, which is really just a small radiator, are plugged. Very small water/coolant passages in both. You may need a new radiator. If this is the case, the radiator is the least of your problems. Getting to the heater core is a big PITA. For your sake, I hope I am wrong.....
Thread Starter
Instructor
Joined: May 2021
Posts: 130
Likes: 27
If your system clogged as badly as you say, I believe your radiator and heater core, which is really just a small radiator, are plugged. Very small water/coolant passages in both. You may need a new radiator. If this is the case, the radiator is the least of your problems. Getting to the heater core is a big PITA. For your sake, I hope I am wrong.....