Temp sending unit

[chengny]

"The one out of old head is 3/4 threads and the vortec is 1/2 "

If I read it right, he means that the sender he has is 3/4" NPT and the hole in the cylinder head is only 1/2". It's already too big - a bushing won't help.

You'll need to get the 1/2" size sender or sometimes the coolant sender hole in the other head is bigger (if you don't mind moving the wire). If it is the right size, put the one you have in the other head.

It is also acceptable to use either the thermostat housing (if there is a free hole) or some people even use an available hole in the intake manifold.