on a 88 where is the coolant temperature sensor and how quick is it to replace it?

 

It's the sensor in the middle of the picture and it's very easy to replace.

 

I replaced mine a couple weeks ago its not too bad, you might want to put a sheet of cardboard under your engine or some newspaper because some coolant will come out of the hole. Just get the new one in the hole quick and your set. If you have the stock gauges make sure you get the sensor with the green insulator (I made the mistake of getting the black one)

 

The picture is the temperture sender. The sensor is on the other side of the intake on the heater rail. Its on the front of the rail near the thermostat housing.