chris81326

I have a 2004 civic ex, and every time I drive over 70-80 mph on the highway for say about 30 miles straight and stop it will start to overheat. The Weird thing is to be that sometimes when I drive over a 100 miles and stop I will see coolant almost purged out of the reservoir. Also, my coolant levels never drop in the radiator and when I run a pressure test on the system it comes back fine. ???????

I have noticed too both my fans ONLY come on when the A/C is on (I thought that was weird).

I have changed:
thermostat
fan switch (next to thermostat)
Engine coolant temp sensor
flushed radiator
Newer water pump installed this year
radiator cap


any direction on what this could be ??????

mikey1

what you are describing here is actually not weird at all, it is unfortunately quite common with these cars/engines, and the cause is a blown head gasket

chris81326

that makes sense....Also is it normal for the fans only to come on when the A/C is on?

Star1967

No the cooling fans should kick in at set temp. best way to check this is pop the hood with the engine running with A/C on and watch the fans. It might activate due to the extra load put on it. With the blown head gasket you will see a white foam on the oil dipstick. How many miles on the engine? The fan sound might be the blower motor kicking in.

mikey1

no....you will not....not with these engines

Star1967

Okay I'm still trying to learn the Honda culture. So how do you tell? I wonder if a hairline crack would cause it?

mikey1

you tell by the overflow bottle puking its guts out

what happens is.....

the combustion gases get pushed out through the blown head gasket and into the cooling system,

this "air" in the system then pushes coolant out into the overflow bottle to the point that it will eventually literally overflow,

the air in the cooling system then causes high temps and/or overheating

you will rarely (if ever) see coolant in the oil (or the other way around) with a blown head gasket with these engines

Star1967

Okay. Also would collapsed or bulging hoses be a sign? Thank you I now know what to look for when it's time to rebuild the 1.7L I have.

ezone

That would be a sign, but not a sign of an engine problem.

If the hoses collapse, that means the cooling system is under a vacuum and that would mean a cap, hose, or reservoir problem, as in there is a blockage or clog or bad part that can't let the system pull liquid out of the reservoir and refill the radiator as the system cools.

Same if there is a blockage and the entire cooling system is under extreme pressure far beyond the designed 13-16 PSI. Yeah you could see hoses swell if they are subjected to well above normal design pressure.

If you have a radiator hose swollen at normal operating pressure, the hose is just garbage.
Oil soaked hoses will do this....shortly before they pop.


HTH

ezone

The fans must come on whenever the AC compressor cycles on.

The fans must also come on when the coolant temp is high enough to turn on the radiator fan thermo-switch. Approx 200*F (I did not look up the spec this time)

Due to the placement of the fan switch in the flow of the system, it can take a long time to get the fans to turn on. A gentle breeze blowing through the radiator can cool the fluid enough to negate the need for the electric fans.

At this time: Is the radiator completely full to the very top or is there an air space in the top?

After engine cooldown, is the reservoir still showing far over full, or does its level return to normal without your intervention?

You overheat when you stop moving, correct?