1971 Temp Sending Unit(s)

[James C.]

My 1971 454/ 4 speed has two temp sending units. One on the drivers side is a unit with a single slide on wire. Looks like the one I had on my 1967. It is hooked up and works fine.The passenger side also has a unit that is not hooked up, but has two one half inch electrical connection spades. It looks very old. Is it common to have both of these. If not,is there a plug that will fill the passenger side hole when I remove the unit. Believe me it leaks tons of radiator water when loosened. I know the guide mentions both types, but is not clear if it is one or the other or both..You gotta love these cars...Jim

[John H.]

Re: 1971 Temp Sending Unit(s)

Jim -

I believe the one on the passenger side is the cold/hot sensor that triggers the vacuum relay for the TCS system so the distributor gets full manifold vacuum if the engine hasn't come up to operating temperature yet or if it's overheating, whether it's in high gear or not.

[Patrick H.]

Re: 1971 Temp Sending Unit(s)

Jim,

Your car requires both.
The two bladed one on the right should have a green wire with a brown "L" or "V" shaped connector. See picture below - the arrow is pointing to where the green wire attaches to the main harness. The brown connector is the one that attaches to the two blades and is hidden by the chrome horizontal ignition shielding.

Your TCS system must not be functioning and/or present if the two bladed sensor has nothing connected to it. The one on the left, or driver's, side is the one for the temp gauge in the center cluster.

Patrick

[Jack H.]

Re: 1971 Temp Sending Unit(s)

With the engine temp switch disconnected (open circuit), the CEC will still function. The 'smart' control relay will simply 'see' the engine is AlWAYS functioning in the 'normal' heat range regardless of actual coolant temp.

That means the time delay relay (engine just started and 15-40 second timer hasn't expired) should still be active along with the transmission control switch (is car running in high gear(s)?). So, at least half of the CEC feature functions will still be operable with the coolant temp switch disconnected.

[James C.]

Re: 1971 Temp Sending Unit(s)

Thanks for the info. I have had the shielding off but I cannot see any wires around the switch or any in the engine bay that are loose. Where does the wire(s) start..The car runs great. Jim

[Harmon C.]

Re: 1971 Temp Sending Unit(s)

Jim
Look in Patrick's picture for the connector it only has one wire. The wire may have been unplugged and the wiring and two prong plug is not their any more.
Vendors sell this wiring harness.
Lyle

[James C.]

Re: 1971 Temp Sending Unit(s)

I noticed Patricks car is a small block.Would big block cars with A/C be the same..Thanks!

[Jack H.]

Re: 1971 Temp Sending Unit(s)

Yes, the CEC (Combined Emissions Control) system was installed on ALL 1971 Chevrolet passenger cars regardless of BB/SB configuration. So, there will be a temperature switch in the RH cylinder head of V8's to serve as a CEC input sensor.

The switch is a single pole, double throw, configuration. ON (shorting to ground) when the engine is either cold or abnormally hot and OFF (open circuit) when the engine is within the normal coolant temperature range. That's why a single green wire runs to a 2-terminal connector and 'daisy chains' between the two terminals...the triggers are COLD or overly HOT engine temp.

[tom444634]

Re: 1971 Temp Sending Unit(s)

Jim,

I also have a 71 LS5 but without AC. The wire that goes to the two terminal sensor is dark green and plugs into the main harness behind the valve cover. I tried to get a decent shot of it, but the angle is tough.........

Tom