Coolant not flowing back into the radiator
 

Hi, Need some advice on my 2004 Honda Civic. The current problem- after the car is driven the coolant going the overflow tank. The problem is the coolant is not returning back to the radiator. I have done a coolant compression test it holds strong at 16 psi. I have done an engine compression test and all of the cylinders are at the same psi. I have also done the test where you check for combustion gases in the coolant, the liquid did not change color. Replace the radiator cap with a Honda radiator cap from the dealership. Replace the radiator itself (from Oreily). The thermostat is from Oreily. The car is not overheating. Any suggestion, I am tired of getting up every morning to extract the coolant from the overflow back into the radiator.

thanks

welcome to the forum have you replaced the drain hose from the rad to the reservoir sometimes it can flow one way but block the return to the rad.

Yes, I did replace the hose and the overflow tanks

Check to see if there is anything blocking the overflow pipe that is on top of the radiator near the cap
Then check to see that the over flow hose goes far enough into the reservoir to reach the bottom
Otherwise when the engine cools it will pull in air instead of coolant from the reservoir
Hope this helps

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I had a similar problem with my 02 Civic LX last summer.
This is clearly a "blown head gasket" or any kind of a small air leak from the cooling system to the atmosphere. You must carefully watch the coolant levels in both the radiator and the overflow bottle.
I pulled my cyl head & found warpage. The previous owner must have run the engine while overheating.
I had a local machine shop shave off .005." The engine has been running fine for the past 10 months now.

You are probably right, I just hate I got hoodwinked by the dealership in buying a used engine through them.

If you did all those test that you mentioned in the opening post then it is doubtful that it is a bad head gasket or warped cylinder head.
No gas leaks in coolant system test, holds pressure
No change in color for exhaust gas in coolant system
Better to check radiator cap and coolant over flow hose

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The cooling system is definitely leaking somewhere. Unfortunately, on these cars sometimes a cooling system leak is very hard to pinpoint.
The leak may only happen while the engine is warm, and be undetectable after the engine cools.
I had the same symptoms on my Civic, and replacing the head gasket and shaving the head solved the problem.
Head gasket failure is VERY common on these cars.
I use ONLY OEM parts on these cars. I've had very good results.

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Did you buy a used engine from a Honda dealership? This sounds really BIZZARE! :-)
Did you get a warranty?
Who did the install?

I thought the issue was the coolant was not flowing back to the radiator after the engine cools??
Now, have a coolant leak?
The system was pressurized and it holds pressure (while engine is cold?)

The cooling system was tested for exhaust gases
And was found .. no exhaust gas detected

So, if it is leaking then it has to be while the engine is hot
Is the coolant flowing back to the radiator when engine cools?
The water pump does have weep holes
Hard to see but leak would be very small