85' chevy S10, 6cyl temp?

My 88 always stayed @ 190 like religion. That was with a GM sender. Broke it when I changed motors & replaced it with a standard ignition one, then it read @ 210 rock steady for 2 years till the sender took a crap & started reading all over the place. Replaced it with another aftermarket one & it read higher yet. Put a GM one back in &, nothing else changed, it read at 190 again all the time. The moral is, depending whose sender you use, it could read anywhere, I'd start with a genuine GM & see what happens. If it fixes you, your done. If not further diagnosis will be needed to see whats wrong.