Cmp c15a gs

[Phil Waterman]

There seems to be a huge variability in the size and location of the temperature sender on the Chevy inline 6. The original 216 engines from all three of my CMPs had the large tapped location rear of the block for the steam relief tube and temperature sender. The recent 1941 replacement NOS head I got for my HUP has only the smaller tapped location about 6" further forward, between cylinders 5&6. My 235 engine has the same small tapped location but it also has a cast boss for the other tapping directly over the #6 exhaust port. While the 261 has the large hole tapped at the forward position between 5&6.

Picture below shows the 235 head before cleaning, and yes this cleanup and is on the 235 engine now.

I have found inexpensive replacement gauges which had a full set of adapter busing to use with the different size tappings.

The steam relief tube is not needed in most conditions except for real steep up and down hill off roading. When the rear of the block may get to hot to quickly and form a steam bubble before the heat causes the thermostat to open fully.

So to some questions: How many people actually ever open the valve?
Lacking the large tapped hole for the steam tube and temperature sensor has any body used heater tube tap on the thermostat housing at the front of the engine?


What ever happened with the problem of the truck stalling when the clutch was pushed in? Has the problem been solved?

Cheers Phil