Welcome to the forum
You will want to do the Glove Test to take head gasket issue off the table before investing any time in other possible problems, it is a free test
Remove rad cap, if coolant is at the top drain it down 1/2 to 1 inch
Remove overflow hose from rad, plug this hole, vacuum cap, gum, putty or ??
Unplug coil pack wire, you want a No Start
Put latex glove over rad cap opening and seal it to rad with rubber band, you can also use a balloon or even a condom, lol, instead of the glove
Crank engine and watch the glove
If it pulses up and down you have a head gasket or cracked head issue
If it just lays there no pulsing then you are good to check other issues.
If it pulses you can find the leaking cylinder by removing 1 spark plug at a time and cranking engine, glove will stop pulsing when that cylinders spark plug is removed.
Reinstall spark plug to confirm.
Cooling system pressure is 14-16psi, rad cap pressure rating.
This pressure comes from the engine heating up the coolant and the coolant expands in volume.
Cylinder pressure is 160+psi when starter motor is turning engine, that's the pulsing you see if there is a leak, after starting, cylinder is 900+psi when firing.
Cylinders are surrounded by coolant, that's the point of the cooling system, so any head gasket issue will always show up in cooling system first.
Coolant in the oil can happen but it was more common on pre-1980's engines.
Your full overflow tanks points to extra pressure in the cooling system.
So best to eliminate that possiblity before spending money on things that won't fix the problem.
Last edited by RonD; 04-19-2016 at 11:20 AM.