Temp Guage

[Its Just Me]

Maybe this should be under Electrical?

My 72 Monte Carlo Custom, 350/350 has the factory dash guage package. Under the hood I have 2 wires and connection points for the factory water temp guage. One on the left head and one on the right head. The right head has a slip on connection and the left has a stud with a nut. My wiring harness appears to be original and not spliced. Why 2 connections for one guage? Is one for a warning light (that I'm not aware of) and the other for the guage?  If so, which is which? Does it take 2 readings for 1 guage and average them?

I'm putting a new autometer mechanical temp guage in and IF one is for a warning light, I would like to retain that as an extra precaution.

My electrical diagram doesn't help.

Any Ideas?

Scott

[monte70car]

Scott I believe the other sensor works with the spark knock. I've seen both the slip on connection and the stud and nut. If you had the dummy light dash then you would just have a water light. But since you have the gauge style dash there is no warning light just the gauge. What you could do is trace the passenger sensor wire back through the harness and see where it goes it could be the sensor failed in the drivers head and someone added the passenger side one and tied it in further into the harness.

[stangeba]

I believe the right sensor is only used for the TCS (transmission controlled spark) system. The Left (driver side) sensor is for the temperature gauge. Mine is a 71, I bought another 71 just for the gauge package. I swapped everything I needed (the entire wiring harness!) but never swapped the right sensor out, or used any of it's associated connections / relays etc.

The TCS system, as designed, did not function until the engine reached normal operating temperature so the car ran better when the engine was cold. TCS,  controlled (prevented) the flow of vacuum from the carb to the vacuum advance on the distributor until the transmission shifted into high gear (or reverse for adjustment and testing). The reason for TCS, was to lower emissions. Many (like my 71 350 4BBL) had this type of equipment removed to try to improve performance. In the process of removing / defeating emissions devices over the years, I bet many got really messed up!

What do you use, full or ported spark?

Bruce

[John S]

Bruce is correct the temp gauge sender is in the left head just one wire. I have a 4 spd that originally had TCS and I have the sender in the right head.

John S

[Paul Bell]

"I bought another 71 just for the gauge package."

A true first gen Monte Carlo enthusiast.

[Paul Bell]

The "general" Chevelle & Monte Carlo engine compartment wiring schematic shows the water temp sensor/switch as being a single unit that feeds the TCS system AND sends a wire into the bulkhead connector for the instrument cluster. To make it more confusing, this wiring schematic doesn't differentiate between idiot light or gauge use.

[Its Just Me]

WOW, I'd never heard of a TCS system.  I learned something today. 

Sounds like I need to use the left head for my new temp guage and I'll leave the right side alone.

If my factory guage proves to be accurate, I'll re-install the factory sender and continue to use the factory guage. 

Bruce, I believe I'm currently using full vac. though I believe I "should" be using ported for emissions reasons.

I'm really curious now how an electronic signal controls vacuum between the carb and distributor.  I think I've got some research to do now.

Thanks all.

Scott

 

 

 

 

 

 

 

[stangeba]

Scott,

Here is a link to my brother in-law's business web page, where he explains vacuum advance.

http://www.langdonsstovebolt.com/tech/vacuum-advance-and-why-you-want-it/

 

Bruce

[MCfan]

 

WOW, I'd never heard of a TCS system.  I learned something today. 

Sounds like I need to use the left head for my new temp guage and I'll leave the right side alone.

If my factory guage proves to be accurate, I'll re-install the factory sender and continue to use the factory guage. 

Bruce, I believe I'm currently using full vac. though I believe I "should" be using ported for emissions reasons.

I'm really curious now how an electronic signal controls vacuum between the carb and distributor.  I think I've got some research to do now.

Thanks all.

Scott

 

 

Scott,

 

In my personal quest to understand and adjust distributor advance mechanisms, I have considered numerous articles and even more personal opinions.  It turns out there are several important considerations that relate to your particular engine and driving needs. I found it best to understand the fundamental principles and operating characteristics of centrifugal, vacuum and digital advance systems and then apply only those that match my engine configuration and driving needs.  IMO, there is no "one size fits all" solution for distributor advance solutions.  Also, just because there are many high tech electronic ignition systems out there doesn't mean you actually "need" one or can achieve significant benefits by using one.

 

Following are links to several of the many on-line articles that I have found easiest to understand, especially the differences between manifold and ported vacuum advance connections:

 

Chevytalk Timing and Vacuum Advance 101 article

 

Super Chevy Vacuum Advance article

 

Go Fast for Less Distributor Advance article

 

Manifold vs Ported Vacuum chart

 

Super Chevy Going Digital article

 

After trying many adjustments myself, I hired a Pro Stock champion to set up the HEI on my highly modified 402 4-speed.  He reset the valve lash, adjusted the carb, curved the centrifugal advance system and completely blocked off the vacuum advance (after showing me the difference in having it connected and not).  Of course, I would never disconnect the manifold vacuum advance on my bone stock 454SS cruiser so it depends a lot on the engine configuration and how you drive the car.  Good luck.