sirgumby1

Hi all!
First time posting, however I have found A LOT of useful information from you guys to help me fix issues with my car!
Today I really need to ask for help though!
I have an 04 Civic EX that had a blown head gasket in December. I took it to a local mechanic and he replaced the Head Gasket, trued the heads and replaced timing belt. I got the car back and it was running great, although I didn't see a change in gas mileage so he took the car back and cleaned the throttle body.
After the cleaning of the throttle body, I took the car on a trip for business (North Alabama -> Georgia -> Florida -> Mississippi) and the car started getting hot. I popped the hood and found that coolant was spilling out through my overflow. Being out of town, I went to AutoZone and replaced my Radiator and Radiator cap and fluid. (I didn't originally see the water coming from the overflow). I finished my trip and drove the car around the city (no issues), however when I am on the interstate for over an hour, pressure builds and water overflows to the overflow tank.
I have replaced the thermostat, water pump, radiator, radiator cap (2x), overflow hose, had the mechanic re-do the head gasket (under warranty) and still the issue remains. I have to drain the overflow every week or it will overflow out the top.
I have also noticed that the system keeps pressure for a long time even after the car is cold. When I open the radiator cap when cold, I can hear (and see) water suck back into the radiator from the overflow.
I'm stumped. All tests come back with no compression leaks, no exhaust fumes in the radiator, no pressure loss. HELP!!!!
Thanks everyone!

kinakoes2

Are there any signs of heater core leakage in the car? Smell any coolant in the cabin when the heater is on?

If not, that's a tough one... if the problem is a loss of pressure AFTER the engine is under moderate load (like freeway speeds)... then checking it hot isn't an option, as the tools needed must wait for temps to drop to ambient. Do check those spring hose clamps, though... sometimes in the heat of trying to make flat rate times, a mechanic can be tempted to get a little rough with parts. I much prefer screw clamps.

I've never had to test a cooling system dynamically (under load when at op temp), as such problems are quite rare... plus as a moto tech there aren't the sources of leakage more complicated modern automobile cooling systems have. But at least from my POV that's the only way to check if such a problem exists...

Have all the cooling hoses been replaced? I also have an '04 EX... and some of my hoses are needing replaced soon. Check for telltales of coolant leakage under the car (perhaps some blue streaks on the engine)? On motorcycles the wind exposure makes tracing even oil leakage a challenge, and since yours overheats on the freeway...

Try this: buy some cheap foot powder spray, and hit suspected areas of leakage with it. It'll adhere to the parts, even on the freeway... but will reveal any leakage if it exists. I'd look for places where a gasket seals in pressure, rather than just a clamp and rubber hose.

ezone

So it's not holding PRESSURE when cold, but it's got a vacuum in the system.....
The radiator cap SHOULD allow coolant to flow freely from the reservoir back to the radiator when the radiator has negative pressure. If it doesn't let liquid flow that direction until you begin to remove the cap, THAT'S a problem.


Typical head gasket.

Typical head gasket.

Typical head gasket.


However: If the radiator level isn't being kept completely full due to a problem with sucking fluid out of the recovery tank as you said above, THAT could be causing the issues you describe.

I would probably do my usual head gasket tests first.....
Then figure out why the fluid isn't getting sucked out of the reservoir after the engine cools down.