Stupid Question #1 (of many), regarding engine cooling system:

Is it standard operating procedure for the radiator to be half full, while the reservoir is completely full, with a cold engine? I don't get it. I went to check the funky coolant dipstick at the reservoir, but the well was completely full. As you may be aware, this dipstick design incorporates slotted cutouts in it that retain the coolant, and shows the current level in the reservoir. It'* often hard to read, but I suppose it works. 'Thing is, if the reservoir is full, (and this is the first time I've seen it topped off like this)... then why is the actual radiator halfway empty?

I left the cap off the radiator, fired it up, and waited for it to come up to operating temp. All the while, I'm monitoring the coolant in both the reservoir and the radiator. I expected that, once the thermostat opened, the levels would "equalize", somewhat, but that wasn't the case. I kept my eye on the temp gauge, the actual coolant level in the radiator, and the reservoir. Finally, after about five minutes, I noticed coolant starting to flow, and the level rise, but the reservoir level never changed. I waited for the electric fan to kick-on, then turned off the ignition.

Yeah, so... then, the coolant expanded and erupted a little bit out of the radiator. 'Wasn't necessarily expecting that. LOL

At any rate, the bottom line is the car runs fine. I was just attempting to check the coolant level, and this is the first time I've ever seen the reservoir completely full, like this. I asked my wife if she'd added some on her own, but she said 'no'.

So... can anyone help me understand what'* going on, here? Thanks.

Check the radiator cap. If the return plug isn't working right this can happen.