I noticed a hissing sound when I parked my car today. It ended up being the coolant in the coolant resevoir bubbling. When I removed the lid, I noticed there was pressure coming out of the hose, causing the coolant to bubble. It gets VERY hot under my engine bay, but the car wasn't overheating. I had just been driving it for a while, and it felt/ran fine. Temp gauge was normal. Any ideas what it could be?

 

Could be a blown headgasket. Bubbling coolant is usually a sign of that. Do a compression and leakdown to see if it is or not.

 

To much pressure, just burp the cap. Put a towel over it, and turn the cap. There is no coolant leaking anywhere.

 

Compression is good, i'll try 'burping' it

 

You dont have coolant leaking anywhere? You dont smell the sweet smell of coolant while your driving do you?

Check you hoses for cracks, and leaks. You may need a new thermostat, there cheap from the dealer though. So it shouldnt be that big of a problem.

 

I got a slight hint of coolant smell, nothing bad at all...

 

DON'T "BURP" THE CAP!!!

On Honda's, they have a breather valve. If you "burp" the cap, it will cause more air to enter the cooling system. Honda's are infamous for overheating with just a small air pocket in the system.

What you want to do is, (while the car is running at normal operating temp) crack the 12mm breather valve open just enough to allow coolant to flow out. Hold your RPM's at 1500 and watch the coolant flow. If you have air in the system, the valve will begin to 'spit'. What you are looking for is a steady stream of coolant. After the stream is established, close the valve (wirst tight) and you are done. If you develop more air pockets in the system, you have a blown head gasket.

The air pockets are most common after a coolant change is performed. Be sure that you have enough coolant in your overflow. Over the next day, keep an eye on the overflow level. The cooling system will pull what it needs from the overflow and vice versa. If you have too much in the overflow, it will spit out what it doesn't need automatically after you shut off the car.

Good luck

 

Oh yeah, the breather valve is normally found near the upper radiator hose on the engine side.

 

Not all Honda's have the bleeder screw. I know for a fact that 99-00 Si's do not.

 

True..