This is correct. There are SOME cars/trucks that have a valve like that inline of the collant to the heater. Toyota trucks like your 4Runner and the little Toyota pickup I used to have are prime examples. The 1989 Jeep Cherokee I used to own also had something similar but was a vacuum operated valve. Many other vehicles run coolant thru the heater core at all times tho like VWandDodge is saying. Dodge Rams are an example of that.

so how does air get into the system to begin with? poor service ? internal engine fault?

leaks, improperly filling the rad and bleeding the system, etc...

Usually it will happen when you drain the system... as the water goes out, air goes in. It's pretty hard to get the sytem 100% empty. There is usually some coolant that is left inside. Depending on where it is at... it can trap pockets of air in the cooling system..

Cartman

I had the same problem, it was caused by flushing the rad and just refilling it. After much searching and a little help from this board I finally got it fixed (the heat workd better now).

I actually took a floor jack and jacked up the passenger side of the truck as far as I could get it, I have been battling this for some time so I got it as high as I could, rear tire was almost coming off the ground

This worked for me, the noise is gone and my heat works.


Chris

No problem. I guess it is better safe than sorry. [&:]

I've been having that problem as well. Never knew what it was though, thanks for the post. I was alsowondering if this could have anything to do with a possible heater core problem. My windows won't defog most of the time (at any temperature) and there is a bit of a smell inside the cab sometimes. Do these two things have anything in common? Any insight would be helpful, thanks again!

Yes, your heater core is shot and I bet it looks like this:

Thanks for the solution to the "girgling" noise and slight smell of coolant (only when running heater for about 30 secs then goes away), but absolutely no leaks of any kind! 99 Ram 1500 I've had this sound since owning it, but never any probs - good heat, good ac (probably could be a bit colder, but that is a work in progress - going to be insulationg my cold ac line with heat reflective tape on top of the aluminum foil wrapping i have since reading about guys REALLYU insulating that cold ac line thickly and having REALLY good results - some with as much as a 10 degree drop in temperature for ac!!) and being I'm a cheap-o, i will do this procedure and keep on truckin!