I've heard in the past a slight machining intolerance in the opening that the radiator cap seats onto which may cause coolant to bypass the pressure cap.

The last two weeks, I noticed my coolant pressure seemed a bit low. Well today when checking my coolant levels, I undid the cap by the engine (on the filler neck) and I noticed my coolant level was a bit low. So I added about about 16oz of water to the system. The level would fill to the top and then slowly drop again. So I added another 16oz and the same thing was happened again. At this point I was fairly suspicious something wasn't right and considered it may be leaking from somewhere but there was nothing. So I get one more 16oz bottle at which point I check the overflow and its full of the water I just added.........
I replaced the cap just 2 months ago and got the Koyo in May or June of this year. I have another new cap which im going to try when I get home.

Has anyone else had any problems similar to this? Any input is appreciated.

 

I have a Koyo, haven't noticed any coolant loss in over a year. Keep us posted though.

 

you should ask koyo about it, because i wanna pick up a koyo radiator, instead of a fluidyne since its so xpensive

 

This is exactly why I opted for a big Brass rad instead of the Al. ones. I have a lifetime warranty