I have an 87 TPI 305 engine, that now sports Trick Flow 175cc aluminum heads. The Trick Flow heads have larger than stock Coolant Temp Sensor threads. Trick Flow said their Coolant Thread Sensor provisions are 1/2" x 14 NPT. Does anyone know what the stock coolant NPT thread size is? I need to get thread inserts to use the sensors.

Any help is appreciated!

GM used 2 different sizes over the years. Lots of older stuff is 1/2" NPT, sounds like yours are the smaller 3/8" NPT size, though.

Thanks very much. I brought the sensor to the local hardware store and it was confirmed to be 3/8 NPT.

Thanks again

You should be able to get an adaptor to use your CTS with the larger threads in the head.

I was able to do this when I did my 400SB swap years ago.

Yep, just need a bushing. 3/8 to 1/2 NPT. Sold at just about every major hardware store (home depot, Lowes, etc.).

I'm going with this bushing reducer from Jegs, since I'm in the process of getting other parts.

http://www.jegs.com/i/JEGS/555/100465/10002/-1