ok we put the heat sensor on the new crate motor and it works fine. it is new and we had a diagnostic tool pluged in, but the gauge on the dash is always saying it is way to hot. but at the same time the diagnostic says a nice 210 degrees.

any ideas what is wrong with the heat gauge?

 

Two questions, what year and engine are we talking about, and which sensor did you replace?

Most 3rd gens have 3 coolant temp. sensors. One is the CTS (coolant temperature sensor), which is what the computer uses to read coolant temp. The second is the coolant temp. sending unit, which is what the temp. gauge in the gauge cluster uses to show coolant temp. The third is the fan switch, which is what causes the fan to turn on at a predetermined temp. (depends on engine).

 

86 iroc new motor is zz4 and there is only one heat sensor

 

That's why the gauge doesn't work then. It needs a resistance signal from a sending unit, and you don't have a sending unit installed.

Normally, the sending unit mounts in the driver's side head, between the #1 and #3 exhaust ports, and has a single green wire going to it. Find the wire, install a sending unit, and hook the wire to the unit.

 

i looked today the sending unit was there but the unit looked old so i replaced it and i am still having the same problems.