Possible blown head gasket

Described problem in my last email and received a reply. Unfortunately, my phone which I sent the first email from, decided to change the word Freeze Plug to Fuel Pump; Which changes things a bit; There was no Fuel Pump replacement. It was a Freeze Plug that the mechanic replaced and the, "noticeable improvement was that the engine's idiot indicator for temperature, went back to a smidge below the halfway mark, which is where it has normally been since 2005, until before the Freeze Plug replacement.
Anyway, when the mechanic did the pressure test and he said he did it a few times said it was fine, so I asked him to pressure test the radiator cap and he said he did and that it was fine. However, that doesn't necessarily mean that he did, because that's just the world we live in now, I guess.
I will replace the radiator cap and see how that goes.
Part of the malfunctioning of the van is that after about twenty minutes of city driving, when I stop at a red light and idle for 60 or so seconds, the idiot light for oil starts flashing and I get the accompanying ding-ding-ding. Put it in park and it stops. Usually I turn it off as well until the light turns green and it starts right up and runs just fine, until the next red light stop and then same thing happens.
I agree that the fluid has to be going somewhere, it's not like it just disappears but what is up with the oil indicator and the ding-ding-ding at the red light behavior?