Which hole is for what?

[Old_iron]

I know one is for heater hose, one for water temp sensor. But not sure which and what the 3rd one is for.

[Steeveedee]

Hole labeled "A" is vacuum for the power brakes.

[DeadheadNM]

350? A is for a vacuum fitting. Temp send unit typically in LH head with the hole in that non OEM water neck plugged up.

[Steeveedee]

Hole "C" would be for a thermal vacuum switch (emissions control), if the temp sensor doesn't go there (which it shouldn't). What year is the engine?

[Old_iron]

Originally Posted by Steeveedee

Hole "C" would be for a thermal vacuum switch (emissions control), if the temp sensor doesn't go there (which it shouldn't). What year is the engine?

I don't remember for sure - I'm thinking 68-72?

So, I'm hearing that:
A is for the brake booster
B is for the heater hose
C should be blocked off

If that is right, then where should the water temp sensor go?

[EagleChief]

Technically, the temp sensor goes in the block on the passenger side, just below the headers, about midway back.

You could put your temp sensor in location "C" if you wanted to. Just make sure the other location is plugged.

[rechinca]

Water temp sensor is in the drivers side head between the front two exhaust ports just above the spark plugs.

[Andy4639]

Originally Posted by rechinca

Water temp sensor is in the drivers side head between the front two exhaust ports just above the spark plugs.

x2 drivers side between spark plugs 1 and 3.
Make sure the tempature sending unit is for a 71-72 truck are the gauge want read right.

[EagleChief]

Originally Posted by rechinca

Water temp sensor is in the drivers side head between the front two exhaust ports just above the spark plugs.

Originally Posted by Andy4639

x2 drivers side between spark plugs 1 and 3.
Make sure the tempature sending unit is for a 71-72 truck are the gauge want read right.

Hmm... mine is in the passenger side.

[TruDom]

Originally Posted by EagleChief

Hmm... mine is in the passenger side.

mine is too but thats because the dakota digital sensor won't fit there with the headers.

[Old_iron]

I just went and looked and there is nothing on the passenger side. On the driver side between the front 2 spark plugs there is a flat area cast into the block, but no hole was ever drilled. Maybe that's why the PO had that water pump neck with the hole in it?
Can I put the sensor there?

[weim55]

Does the side of your cylinder head between cylinders one and three on the driver side and cylinders six and eight on the passenger side have this water port plug below The arrow? This is where the temperature sensor is supposed to go.

If your cylinder heads do not have accessory holes on the ends of the cylinder head you have a set of 1968 or earlier cylinder heads that would’ve used an intake manifold with a second port in the front for the temperature sensor. (the 2nd picture shows '69 and later heads that DO have the accessory holes) 'The early heads usually do not have a port on the side of the cylinder head for a temperature sensor.

On my truck a 69 with a factory 350 power brakes, AC, and turbo 400: Port A in your picture is used for vacuum to provide vacuum for the HVAC System, vacuum modulator on the automatic transmission and vacuum supply for the power brakes. A three-way tree screws into that port to supply vacuum for all three of those functions.

You could use port "C" for a temp sender but I don't recommend it. That port is on the cold side of the thermostat and your temp gauge will not read actual engine temp until the thermostat opens. (the gauge will read cold while the engine warms up then spike to actual temp when the thermostat opens) AND if you try to use that port for the temp sender you must check and make sure the temp probe does not hit the thermostat beneath it as installed. If you have no other ports available for that temp sender I would find another intake manifold with 2 ports on the water side. Small block intake manifolds are dirt cheap and easy to find with the configuration you desire.

Steve weim55 Colorado

[71CHEVYSHORTBED402]

"Which hole is for what?"

That's what she.............Ah, never mind

[siggyfreud]

I've used C for a thermo switch for radiator fans. It works well because it's not kicking the fans on until the thermostat is open anyways, and is "good enough" for the on-off temps in terms of accuracy on actual engine temperature.

[68 P.O.S.]

Originally Posted by EagleChief

Hmm... mine is in the passenger side.

The temp switch for the TCS system goes there. Did your truck come with the TCS?

[Larry Weaver]

The hole in the water neck is for a ported vacume switch.

[GASoline71]

Originally Posted by Steeveedee

Hole labeled "A" is vacuum for the power brakes.

Every 67-72 SBC truck with an auto transmission I've owned or worked on had the modulator for the transmission plugged into that port. The vacuum for the brakes has always came off the back of the carb.

Gary

[68 P.O.S.]

Originally Posted by GASoline71

Every 67-72 SBC truck with an auto transmission I've owned or worked on had the modulator for the transmission plugged into that port. The vacuum for the brakes has always came off the back of the carb.

Gary

This ^^^

[rechinca]

Originally Posted by 71CHEVYSHORTBED402

"Which hole is for what?"

That's what she.............Ah, never mind

We can close this now, Tony wins the contest!

[EagleChief]

Originally Posted by 68 P.O.S.

The temp switch for the TCS system goes there. Did your truck come with the TCS?

TCS? My lack of knowledge automatically makes me think of Traction Control System, but I know that's not what you're referring to.

It took me a minute, but I had to realize my motor is supposedly out of an '88 Suburban, so maybe that's why mine is hooked up different? :shrug:

[68 P.O.S.]

Haha, of course. Transmission Controlled Spark. It was an early emissions thing that didn't really do much. It would stop the vaccum advance from working until the engine was fully warmed up (temp switch in passenger side head) and the transmission was in high gear.