Coolant Resivour backfilling

Hey my fellow 6th Gen owners..... I am having an issue with my F23A4 02 Honda Accord Coupe where for some odd reason coolant is backfilling in to my resivour and I can't find out why. I have a brand new radiator, brand new thermostat and gasket, new upper and lower radiator hoses and new hoses for the thermostat housing which go the the breather valve on the intake from valve cover to the thermostat housing and to underneath the throttle body. When I replaced the thermostat housing I never filled the resivour and it's completely full now. I continue to lose coolant every day and have to continue to fill my radiator every day. For awhile the engine would start to run hot when I would have the AC for about 20 minutes or less but once I would turn it off the temp would go back to normal. Even while sitting at a stop light with the AC off the temp gauge would start to rise until I started moving again the temp would go back to normal..... Can everyone please help me out to get this problem fixed please I would greatly appreciate it

The radiator cap are new?

New radiator and cap


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If it is filing the reservoir, it is possible that there is air leaking into the system somewhere. The reason for this belief is that coolant under pressure boils at a higher temp than coolant that not pressurized. I would check and clean all hoses and verify the condition of the radiator cap.

James the radiator cap was brand new when I bought the radiator.


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Exhaust out of tailpipe smell sweet?

How are heater hoses?

Sino exhaust smells like fuel..... And xci all my hoses are brand new


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Are you able to do a compression test?

Yeah, if you have no visible leaks, coolant can be burned (compression test) or come out the cap.

I still suspect your cap doesn't fit correctly, but you'd see the coolant tank overflowing.