Unfortunately, i think I know why, but i'm looking for collective knowledge and experience here!
so: I have one of those pressure caps on my overflow reservoir - old school - lift the red tab, it releases pressure! But in this case, i can lift that lever 3 days after the car has been driven, and it gurggles and bubbles in the reservoir, once that pressure is released the bubbling stops. anyone want to guess? No white smoke, no haze on the windows, can't smell Antifreeze, so I'm a bit stumped here.
I also have what I consider weird temp gauge readings, gauge is accurate, but it shows stone cold when radiator is full and vehicle is running, but acts like there is a bubble in the system other times, with a spike in temp gauge 3/4 toward hot, then immediately back down into cold (within 2 or 3 minutes) I've been been "bleeding the system repeatedly for 2 months now - heater full blast, top up radiator through the cap/bolt, top up reservoir.
I'm figuring lets solve the pressure issue first, i suspect everything else will fall back in line after that = so whats your best guess/ experience?