Rep Power: 0

Hey everyone, 2005 civic LX Coupe 1.7L V4 here.

I am having an overheating issue that only comes on at high altitude. Most of the time but not all the time when driving up a mountain where I live, my engine will start to rapidly heat up. On one occasion, I pulled over and noticed coolant around the outside of the filler cap as well as a boiling noise coming from the engine. I tried tightening my radiator cap and the torque came loose, sort of like when you tighten a crappy bottle cap so much that is becomes loose again. Is that normal? Would a bad seal on the radiator cap cause these type of problems?

 
Rep Power: 512

Yep. Has a bad rad cap on my 2002 and it caused overheating. The rad cap is meant to keep the coolant system, usually a closed system, below a certain pressure threshold. 1.1BAR IIRC. If it's not keeping pressure, it's allowing coolant to "vent to atmosphere" when the coolant expands with temperature increase. This can cause air introduction into the coolant, which leads to inadequate cooling. Hopefully temps didn't rise too much to cause head warping. Replace rad cap, thoroughly burp your coolant system, and check again. Wouldn't hurt to check your thermostat for proper operation while you have the system drained. Literally remove and put in a pot of water on the stove. Helps if you have a thermometer to check when it starts to open, fully open, and fully close. If you don't have a thermometer that goes from like.. 100-250, just make sure you see the valve open and close when the water gets hot and when it cools