Rep Power: 0

My car was leaking oil out of the valve cover and I just replaced it. Was over heating bad because the thermostat was broken but I just put a new one on with a new gasket, engine temp reads pretty accurate now. Also just put new spark plugs in because of a code for a misfire. Spark plugs didn't fix the misfire problem.. Car is now driving and sounding ok except for the heat not working (heat worked before the thermostat went) and if I drive it for over 20 minutes (not beaten on but normal driving around town) it'll over heat and stay at about 3/4 up. Nothing else noticeable, car starts right up and is not loud or shaky. No smoke coming out. Oil is good, there's no oil on the on the coil packs. Car is a 02 civic ex 1.7 vtec d17.

 
Rep Power: 209

Monitor the coolant levels in both the reservoir and radiator for a few days. If the radiator is losing water and reservoir gaining water that is a sign of a possible head gasket breach. If coolant is leaking internally into cylinder #3..that can casue a misfire. Pull spark plug when engine is cold (sitting over night) and see if it's wet (cooolant). If it's not wet it doesn't mean coolant isn't getting into cylinder.

 
Rep Power: 517

Liquid would just go directly to the bottom of the cylinder (top of piston or escape past the rings), the spark plug is at the top of the cylinder in the head.
The plug would not get wet until AFTER he tries to start the engine.


He could leave the plug(s) out and crank the engine over and see if liquid sprays out of the open plug hole


I think op probably still has an airlock in the heater core causing no heat, more cooling system burping may be needed.
If it continues, do head gasket checks?