1970 350 Temp Ports ?

[driller35]

I have a 1970 Chev CST with 350 Auto, AC and have a question on the temp ports on head , I know one is being utilized by the factory temp gage and I am wondering what the other one would be used for and can only think for the AC but am not sure , I want to be able to use port for Sniper EFI

Thanks

[clay68c10]

Use the other port for your EFI, the AC didn't have a temp sensor input. Someone in the past may have just stuck a sensor in there to block the port instead of a pipe plug.

[driller35]

Thanks Clay68c10, funny thing is though both are used and wired and both look to be factory , trying to follow the wires all lead into to the main harness

[68 P.O.S.]

The use of the two ports in the heads depend on your gauge panel. If you have the 7 hole gauge panel with actual gauges, the drivers side port is for the temp gauge. If you have the 3 hole panel with the dummy lights, the passenger head port is used for the temp light switch. Its weird that yours is using both locations...unless the PO hooked it up because he wanted to use both gauge and light

[demian5]

I have one on each head and they are both hooked up as well. I have a factory temp gauge.

[68 P.O.S.]

Originally Posted by demian5

I have one on each head and they are both hooked up as well. I have a factory temp gauge.

Hmm, interesting. From what I've read on this forum, you had one or the other depending on your gauge panel, not both. Does anyone know the correct answer??

[driller35]

Well I unhooked the passenger side and do not notice anything out of the ordinary, factory guage still working and that corresponds with the drivers side still hooked up

[ray_mcavoy]

That temperature switch on the passenger side cylinder head is likely for the TCS (Transmission Controlled Spark) system. It was an early emissions system used on some of these trucks that blocked vacuum from reaching the distributor vacuum advance until the transmission was in high gear (used with both manual & automatic transmissions). The system used a temperature switch so it was only active once the engine was up to operating temperature.

Trucks with TCS, a small block V8, and factory gauge cluster usually had the temp sender for the gauge located on the driver side cylinder head and the temp switch for the TCS on the passenger side cylinder head.

[driller35]

And was this used on the TH350 and TH400, and if unplugged what differences would one see Thanks

[ray_mcavoy]

Originally Posted by driller35

And was this used on the TH350 and TH400, and if unplugged what differences would one see Thanks

Yeah, TCS was used on various GM cars & trucks throughout the 1970 to 1974 or so year range. I believe it was only used with certain engine/transmission/vehicle combinations but I have seen it used with both manual & automatic transmissions.

I think it was fairly common for folks to disconnect or bypass the TCS system to improve driveability so it's possible yours might not even be hooked up anymore. If so, unhooking it's temp switch won't do anything. But if it is still functional, unhooking the switch might cause some driveability issues by retarding the timing when the engine is cold.

To see if the system is still hooked up, take a look at the hose on the distributor vacuum advance. Follow it back from the distributor to see where the other end is hooked up. If it goes directly to a port on the carburetor or intake manifold, then the TCS has been bypassed. But if the hose goes to a solenoid valve (often mounted on the intake manifold), then the TCS system might still be active (assuming the rest of the wiring is hooked up).

[driller35]

Thanks Ray, yes all still hooked up vacuum wise and with solenoid still hooked up to electrics , I will have to bypass all this for efi but at least now know what this assembly is used for , I unhooked the temp control Fri and have put on over 400 miles with out noticing any difference

[68 P.O.S.]

Ahhh, the TCS Makes complete sense now, I didn't even consider that. Good call Ray, mystery solved