Radiator Issues
 

So here is the deal with my 87 Runner. Minus the details, I had to replace the intake manifold over Christmas, and after that used a recommended “back flushing” kit to attach a garden hose to my heater hose and flush out 25 years worth of rust. After this, my heater ACTUALLY WORKED!! Which was amazing. Anyway, to the problem at hand…..I filled my radiator about 2 weeks ago, and checked it the other day. I filled it to the tippy top (which took about ¾ gallon), drove about 45 minutes in traffic and stopped for a quick bite. When I stopped, water and radiator fluid were pouring out of the radiator, and out of the overflow. It always seems to be low and takes at the minimum about ½ gallon to fill. Is there something wrong? Should I be worried, or should I not worry about the coolant level being at the tippy top?

Advise me please, and thank you in advance.

replace the cap first. sounds like its bad.

You might have had a small leak the whole time and when you flushed it,you flushed out the dirt and crap that was slowing the leak down or stopping it. It happens quite a bit. I know you don't want here this but....depending on the condition of your heater core,it might start leaking too,or other parts of the cooling system for that matter.It doesn't mean it's for sure gonna happen,just keep an I on your cooling system.