Car is a 1998 honda civic ls swapped ex. My car will run at normal temp for a while, then will start overheating. I went to bleed my coolant system and there was a ton of air in it and the bubbles would not stop coming. There is a high picthed humming noise coming from my intake that sounds like air being sucked into a small hole. I found out its coming from my iacv on the back of my intake, because when I plug the hold on my throttle body for it, it stops making the noise. Could my coolant system be sucking in air from my iacv somehow?

 

Possibly a blown head gasket.

 

Check for white smoke coming out of your exhaust when the car is reving. If so, head gasket.

Kev

 

Also make sure your coolant lines are routed properly.

 

I just changed my headgasket last weekend. From what I can tell it's still good.

 

It also seems like my temp will jump around below normal operating temp when I hit bumps and stuff sometimes.

 

When I changed my head gasket, I noticed my intake manifold was really dirty, so I pulled it off and pulled my throttlebody and iacv off and sprayed it inside and out with brake cleaner and a pressure washer. Then after I got it reinstalled it started making that humming noise. It has never done it before then.

 

I also changed my thermostat while I had everything torn apart, because my old one was stuck closed.

 

two things, are you going off of your dash temp gauge and saying its overheating, or is the car doing something to make you believe it?
And did you try cleaning the IACV with carb cleaner, or did you pressure wash it too?

 

did you do it right?
new headbolts. (good idea)
torque it to the correct specs.
did you make the headbolts snug, then torque to 22lbs then to 53lbs doing it in a sequence?
if you don't do it right you can have a blown headgasket again.

 

Yeah I got arp's and torqued them all to spec. Usually when I've blown a head gasket my coolant gets really dirty from the oil and its really obvious but from what I can tell its still normal colored.

 

Well my dash gauge said it was overheating, so I pulled over and the engine didn't feel all that hot. So I thought my gauge was just going bad. But when I went to open the radiator cap coolant and steam went everywhere. And yeah I sprayed the inside of the iacv with carb cleaner.

 

I am not sure why someone would pressure wash the iacv and throttle body, carb or brake clean is plenty.

As for the head gasket, did you check to make sure it was not warped, did you have it machined, or straight edge and feeler gauge at least?

You might have a bad gauge, check the coolant temp sending unit.

 

I never said I pressure washed the IACV and throttle body... I said I pressure washed the intake manifold... And yes I straight edged the head and block.

 

Could it be possible that air is leaking in through my radiator cap? I have never changed it and it looks a little worn..

 

it does sound to me like you're overheating some, but i also think your temp gauge is going bad, from the fact that the needle falls when you hit a bump. (maybe losing power or signal for a second?)

did you try bleeding the cooling system? if there's air in it, you can bleed it out.

I'd say replace the cap anyway, if it looks worn enough for you to bring it up, it's a cheap enough fix to just go ahead and do.

 

Oh yeah, I'd check the hoses to the IACV too.

 

you said you have arp studs. you don't torque studs down. you tighten them til they "stretch" to the proper clearance.

 

Stupid q, how do you tighten studs? is there a place for wrench?

 

Not too sure what you mean by this. I installed them exactly as the instructions say, and I had a buddy help me that has experience rebuilding motors.

As for the overheating issue, I replaced the radiator cap and topped off the coolant, and so far so good.

I did notice that the coolant was abnormally low when I put the new cap on though. Any way I could lose coolant through a bad cap?

 

You could be losing it if it's steaming out from under the cap, yes.