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my boy has a 93 civic ex i've been helping him work on. he has an overheating problem d16 single overhead cam. it overheats with'n 4 days max. no leak of antifreeze. no antifreeze in the oil. replaced the thermostat, cap 3 times, top hose, bottom hose, bypass hose, fan works could use replacement but works fine enough, sealed a leak around the botom of the throttle body, radiators been replaced, just don't see antifreeze leaking anywhere, and again not in the oil. told him i'd ask on here see if anyone came across this problem before. Thanks in advance.

 
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could be blockage somewhere in the system. you could put some dye in and see if it is circulating. also is heat working?

 
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When does it overheat?

Flying down the highway at 70?
Sitting the McDs drive thru?

 
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the heat does work.

he said after three days it's either or. it could just start overheating driving down the highway he throws the heat on it drops, or he could be sitting at the gas station it could start or when he takes off. then he has to wait for the motor to cool down and top it off with antifreeze but lately he's been using water because he said it's getting pricey buying antifreeze all the time. so he will switch back and fourth. just going off what he told me to type out.

 
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Putting in dye would be a good idea, to see if you have an external leaking problem.

Is he getting any white smoke out of the exhaust? Could potentially be a headgasket problem.

Let us know what you find.

 
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no smoke. when he gets off work i'll tell him about the dye. thank you

 
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I'd guess it overheats after the coolant gets low, it just takes 3 days to lose enough liquid to cause the overheat..

So how low is the radiator when it gets checked? What about the reservoir?

How about checking and filling it BEFORE 3 days are up?

Do you have access to a cooling system pressure tester?
You could put pressure on the system overnight, see how much coolant and pressure is lost next morning, and see where it went.
Pull the sparkplugs out and see if the missing coolant is sitting in any of the cylinders.

You could also apply 150+ psi to each cylinder like I do to prove head gaskets on the 7th gens.

Just a thought.