1/2 Theaded Hole in SBC Cylinder Head

[dhenderz]

I am wondering what the 1/2 inch threaded holes in my SBC cylinder heads are for (see pic). These happen to be Edelbrock e-street heads. The heads came with plugs, which I installed. There is one in each head. Are these open to the coolant passage? Other?

I ask because I need to find another location for tapping into the coolant system. The Edelbrock intake (that came with the ProFlow4 system) only has 2 threaded spots. One is already being used for the coolant temp sensor for the ProFlow4 computer. That only leaves 1 open spot. But I need a location for a coolant temp sensor for the cluster gauge. And I need a location for the heater core feed.

If I understand the coolant flow in a SBC properly the port on the water pump (which is currently plugged) is on the vacuum/draw side (of the pump), not on the feed side. The only way of getting a coolant feed is to tap into the intake somewhere. Or, are either (or both) of those tapped holes in the cylinder head a possible feed point?

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[idahovette]

My 75 K20 350 has the temp sensor in the left (drivers) side head where you installed the plug. Can you use the other side plugged hole for your Proflow system and use the intake location for coolant routing?

 

[dhenderz]

My 75 K20 350 has the temp sensor in the left (drivers) side head where you installed the plug. Can you use the other side plugged hole for your Proflow system and use the intake location for coolant routing?

Or, can I just use one of the cylinder head holes for the temp sensor, like you have on your truck. And then use the 2nd hole in the intake for the heater core feed? Sounds like you've answered my question. These threaded holes in the cyl heads do in fact go into the coolant passage???

 

[idahovette]

yes they do!!

 

[75gmck25]

The stock GM temp sensor in my '75 was installed in the driver's side head at that location. However, IIRC it had 1/2" threads in the iron heads and 3/8" threads in the new aluminum heads I purchased. I ended up moving the stock sensor up to the Edelbrock intake manifold because it also had a 1/2" threaded fitting.

I still use the head fitting for the sensor on my mechanical temp gauge, since I like to have a gauge that works even if my electrics are flaky for some reason.

Bruce