Got a 71' 307 chevy that previous owner put in m 87 K5. Per my build post i am having to sort out all the little issues they left. I have it running almost perfect (needs a new wire and plug set) and now i am on to fixing the gauges on it.

Water and Voltage do not function, voltage i can handle and i know how to test the sensor and gauge on the Temp.

But i noticed a extra sensor on the block and not sure what the hell it is?

This is my first 283-327 series motor i have had dozens of 305-400 motors and do not remember this being there.

 

Here's a thought. Remove it and see what runs out.

I suspect it's in coolant passage, as every pic of a SB head on google images has the hole for it.

chevy small block head - Google Search

Then click 'images'

Obviously, though, you dont want to run your temp gauge from it.
Might not be a bad idea to run to light if lite is separate from gauge and it's a switch which I bet it is. Is there one on the other head? You can run switches in parallel.

 

Makes sense its in the same spot just opposite. I guess someone just used a sensor to fill a spot in the head instead of a plug.

If my sensor is bad i may test that one with a jumper and swap them.

Project Poor Man's Toy needs all the free parts it can get.

 

Pretty sure you'll find it's a switch. Easy to test that.. if it reads open with an ohmmeter, then that's it. If it reads some resistance equiv to the gauge sender on the intake then it's a temp sender.
- actually it COULD be normally closed switch, depending on the purpose of checking temp there.

Why would they do that? Ever had low coolant and watched the gauge? It will lag engine warmup, then suddenly shoot up past normal.

Just guessing of course.

BTW: The sixties SBC's did not have that hole. That's the last time I dealt with them up close and personal.. everything from the single point to the double hump castings. {375}

 

It's a second sensor they used to plug the hole, fixed primary sensor, the wire connection with the connector was bad.

Now I just need to find the wire coming out from under my dash that goes to voltage gauge and ill have them all working.