Air trapped inside radiator after adding coolant

Question

It has now happened twice to me that after adding coolant to the radiator, when I turn the car on the RPM's will bounce up and down and the engine is reving (between 1k and 1.5k RPM's). Normal idle is 750 RPM's. After a while it will eventually idle fine, but usually only after driving it for a bit.

Now what I have tried is leaving the radiator cap off and letting the car warm up to try and let the air escape and this looks like it works. The coolant level rises all the way to the top and will eventually 'burp' and go back down. I've let it run for about 20 minutes. But there still seems to be air trapped inside as startups still has rough idling.

I have seen some references to a bleeder valve, but my car doesn't seem to have this (2002 Honda Accord). Is there any better way to get the air out?

Answer 1

Here's a thread from honda-tech.com. Sounds like you should have one from the factory, but it's possible an aftermarket thermostat housing was installed minus the valve.

If you really have no bleeder, you could install a thermostat housing that has one, or pull yours and install one yourself.

Otherwise, you're on the right track, though you might try running the heater and squeezing the hoses to move air bubbles along. Be careful poking around the engine bay with the engine running, don't loose any fingers. Gentle prods from a rubber mallet might be a safer strategy. You also need to wait for the engine to warm up and for the thermostat to open, otherwise you could have some air trapped in the block with no way out.