please help-overheating/cooling system issues?
 

I've recently had on-going issues w/my cooling system/overheating. It's a civic dx 1.5L (260,000 mi. rebuilt motor).

I have no experience w/cooling systems and am not mechanically inclined, so i'm just hoping to get some info to help me decide where to go from here and possibly what tests can be done to determine the cause and repair costs for a mechanic to do the work. sorry for the long explanation but I don't want to leave out something important.

Started having overflow getting a llittle low intermittently around feb/march, noticed small spots of antifreeze on ground intermittently after parked. Kept adding to the overflow as needed, never letting it run out. A mechanic checked but couldn't locate a leak so pressure tested it and tested fine. Then one day it overheated-temp gauge about 3/4 of the way to the top-I immediately pulled over turned it off when I noticed and the overflow was high-over the max line where I had filled it to. Let it cool for an hour than filled the radiator up with 50/50 and drove to mechanic, temp gauge ran right below the middle, as it usually does, all the way there and they found the water pump had been the cause of the leak and replaced the timing belt and water pump and rad cap. Then a month later it overheated again unexpectedly, as I had not checked or added fluid as I thought was fixed and it had run out in the radiator and boiled over in the overflow, this time the heat gauge just about red lined so I immediately pulled over and the radiator was low but the overfill was to the top of the bottle so I waited over an hour then filled rad w/ 50/50 drove to mechanic gauge in normal temp range all the way. They said couldn't duplicate the issue to diagnose it but said pressure test showed rad cap tested bad so they replaced it and since then no overheats (per gauge) but overflow keeps bubbly over while driving. I had the radiator flushed and a new thermostat put in recently and per the mechanic there was rusted metal particles in the antifreeze when it was drained. the radiator is about 13 years old but they said not seeing any leaks in it.

Thanks in advance for any help.

It could be a bad head gasket or a very small crack somewhere in your cylinder walls.
(note: rusted metal particles would indicate air is being forced into your cooling system somehow. so would bubbly overflow res.)

Have the mechanic test your coolant for combustion byproducts.

take care,
ChrisS