Im not familiar with the ztechs...but it sounds like a water pump. I know the Duratechs use a plastic impeller in threre water pumps witch cause them to go out early.
You may want to check to see what kind of impeller is used on the Z tech water pumps. If its plastic I reconmend changing it.....and that might solve your problem. Look in to it....I hope it helps
ROZ
