I have an 88 GXL that has had cooling issues since the day I bought it a year and a half ago. I have chased down all the leaks and replaced several hoses. I have replaced the Water pump, T-Stat (OEM from Mazda dealer), and I just put in a CSF 2 row copper/brass core rad today. I also had the cooling system flushed by Firestone a couple of weeks ago (I didn't let them add sealer to the system). My temp gauge is reading at about 1/3 in city driving or at a stop but when I take it on the highway (80mph) it runs maybe a needles width under half. I am under the impression that S4's should run at 1/4 between the bottom and top lines of the gauge. Anyone have a suggestion?

I should note that I'm not really a fan of aftermarket gauges b/c I know that's where half of you are probably gonna jump right off the bat. If I really get to feeling desperate I might get one just for diagnostic purposes... they just look tacky to me. Unless of course you have it in an actual race car or you autocross or something.