Rep Power: 0

So, I have read through all of the thread and don't see exactly what our car is doing. It looks like I have a few tests to run to decide what the exact issue might be. We have a 2005 Civic LX 140k. While we were driving the car hesitated a little and then started steaming out of a small hole in the radiator cap neck, then died. The hole is just below the flange out on the "neck" of the radiator just below the cap about the same height as the intake hole from the reservoir. Would not restart while it was warm, winched it up on trailer, let it set over night, it started right up and drove in our barn so I could dig deeper. Added maybe a cup in the reservoir, and 2 quarts in the radiator itself, it ran for 20 mins with the rad. cap off. No sign of bubbles in the rad, but steam starts coming out of the rad. after 20 mins, and heat went cool in the cab. Put he cap on real quick to check and see if it puked out of the reservoir, and it just "steamed" out of the side of the neck. Shut it off and the reservoir is at same level and radiator is a little low but i can see the coolant down in the neck. The temp gauge never leaves 1/2. We just purchased the car in November and have not put 2K miles on it, radiator looks newish and so does the cap. Let me know your thoughts, so I have a little direction to start. I will do the home carbon test to see what it says. TIA

 
Rep Power: 126

Sounds like your cooling system isn’t pressurizing. If there isn’t a leak somewhere, you have a bad head gasket.

 
Rep Power: 223

Post a photo of this "hole" in the neck

 
Rep Power: 211

If it doesn't have a Honda genuine radiator cap it's best to replace it with one. When you watched for bubbles with the engine idling and rad cap off did you rev the engine while observing current flow in the radiator? That is the easiest way to find out if the water pump is working correctly. A water pump can partially fail and may not cause an overheat situation, but does not cool the engine properly. Water pump failure is not common on these engines, but is still a possibility.

Thermostats can also partially fail (closed position) causing insufficient flow which may or may not cause an overheating problem.
Also, you may want to bleed the cooling system of air per the service manual.

As chezboat already mentioned a breached head-gasket is a possibility. Losing coolant in the radiator and gaining coolant in the reservoir is a strong sign for a head gasket breach. Sounds like you're going to do a Block (combustion) test on it? That's a good place to start and if the blue test fluid turns yellow or green then proves a blown head gasket. However, if the test is negative ( test fluid stays blue) that unfortunately does not rule out a head gasket breach.
A leak down test for head gasket breach is the most reliable test.

 
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I did rev the motor to check for flow/ bubbles etc., i saw flow with no burps or bubbles. Our weekdays are super busy for me and mine so I apologize for the delay and thank you for all of your quick responses.

 
Rep Power: 223

Get a new rad. Denso is the oe supplier

 
Rep Power: 225

Yeah, that shouldn't be there. As mentioned, new radiator. Make sure you fill and burp properly, then make sure there are no other issues.

 
Rep Power: 211

OP...for future reference please post pertinent pics on your first post. I just wasted 10 minutes of my life on my previous (lengthy) reply, when I could have summed it up in "replace radiator".
That's 10 minutes of tik-tok ***** twerking videos I could have been watching