Hi everyone I recently bought a 1998 civic ex d16y8 it will not over heat on short trips (10-20miles) but the overflow tank will fill up to the point where it sprays out. On 100+ mile trips it will start to warm up, I turn the heater to full blast and it goes back down. I changed my thermostat, raidator cap no air in the system. Oil and coolant do not appear to be mixing. I know it might be a head gasket but I have no other symptoms of a head gasket leak. And I can't help but think if it was a head gasket it would be on all trips long and short. So what else could it be need help thanks everyone