C3 Temp sensor question, 327

[Ed Driscoll]

Hi Guys,
I have a temp sensor near the water intake, and this is indicated on my schematic as the location for the 18G dark green cloth covered wire. I also have another sensor on the right side of the engine just in front of the #8 cylinder. What is the function of this sensor? Does it share the lead from the other sensor? That doesn't make sense if we're interested in a "water temp" measurement as the gauge indicates. I can't seem to locate any other info about it.
Thanx
Ed #38868

[Jack H.]

Re: C3 Temp sensor question, 327

Sounds a little hookay to me (two temp monitoring devices on a correct/original 327). When the 350 engine came along, the emissions system grew in complexity with slight differences between various years. The temp sender was moved from the intake manifold to the LH cylinder head (between #1 and #3 plugs) and correct factory original senders are AC 6500759 using a single 'pin head' terminal vs. prior era 'T-head' post.

Since cylinder heads come in pairs that left the LH side with a 'temp sender hole' between the #6 and #8 cylinders. Instead of simply plugging the 'extra' hole, a single pole, double throw thermal switch was installed there having two spade lug connectors. The switch was closed (to ground) when the engine was cold, open circuit at normal operating temperature, and again closed under abnormally high or 'overheat' conditions.

In '70, the cold/normal positions of the RH bank thermal switch was used to fire the TCS relay and provide vac advance to the distributor for faster initial engine warm up. The overheat side of the switch was used in some cars to trigger a warning light on the dash. In '71, the cold and overheat positions of the thermal switch were used to over-ride other controls of the Combined Emissions Control system to boost curb idle (fast warm up AND speed air flow through the radiator in the event of stop/go traffic on a hot day with coolant temp 'flirting' with overheat conditions). In later years, the meaning of the thermal switch changed again.

Bottom line, in a bona fide 327 configuration, my hunch would be someone's replaced a factory original cylinder head with a later era head and simply left the thermal switch installed to act as a 'blind plug'....

[Joe L.]

Re: C3 Temp sensor question, 327

Ed-----

You didn't mention what year car you have. Since you're thread title mentions "C3" and "327", I'm going to assume that you have a 68. That was the only year that "C3" and "327" applies.

For 1968 327s, the temp sender was on the left side forward cylinder head. The corrollary position the the right side cylinder head (betwen #7 and 8 cylinders) was plugged with a pipe plug. The temp sender remained in the left front cylinder head position for the remainder of C3 production. As Jack mentioned, the right rear fitting was used for the TCS switch. This began in 1970 for California-delivered cars only. In 1971, it expanded to all Corvettes.

[Jim T.]

Re: C3 Temp sensor question, 327

Joe reference your post about the the 1970 Corvette having a temp unit in the right head for the TCS for CA cars only. My original owner 70 was purchased in TX and it had the temp unit for the TCS in the right head with two terminal connections.

[Joe L.]

Re: C3 Temp sensor question, 327

Jim----

Yes, you're correct. The TCS was used for all 70's; it was the EEC that was California only for that year.