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My 1971 LT1 temp gauge only shows about 150. I plan on replacing the thermostat and possibly the temp sensor(s). My questions is how many temp sensors do I have. I see a single prong sensor on the drivers side and a two prong sensor with jumpber on the passenger side. Are both of these temp sensors and how can I test these. Thanks.
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Re: LT1 Temp Sensor
The sensor in the left head is for your temperature sending unit - that is the temp that your instrument shows. The two prong sensor in your right head is for the TCS, Transmission Controlled Spark. It has nothing to do with the indicated temperature in your dash. Read the archives about poor temperature indications from repalcement Delco sending units. The latest Driveline has an ad from a vendor who claims to have sending units that are properly calibrated.
The TCS unit can be tested to see if all of the components work but the best bet is to turn to your GM Service Guide to run the test. But that is a different question.
Gary -
Re: LT1 Temp Sensor
As Gary mentions, there are two items here; the temp sender (single contact) and the temp switch (double contact). The original temp sender used on your '71 had a 'pin' head connector instead of a T-head terminal, but these have been GM discontinued for a long time.
Most cars from the '68-71 era with replacement temp senders use the T-head terminal style and the wiring harness is ususally modified to remove the factory original 'barrel' connector meant to slip over the 'pin head' terminal with a slide connector intended to install onto the T-head style temp sender....
Reports say, the reproduction 'correct' temp senders now available are 'correct' to an extent.... They're reported NOT to have the factory original AC emboss on the neck band. If true, while perhaps correct in function, they're NOT correct in configuration.
The temp switch is intended to make input's to your car's, 1-year only, CEC (combined emission control) system. During cold engine operation the switch is closed and on terminal should be short circuit to the case, or ground. At normal operating temperatures, the switche opens and you should see infinite resistance between BOTH terminals and case/ground. During HOT engine operation (+230F) the switch again closes and the opposite terminal will short to case/ground. That's why a single wire daisy chains to both terminals....
The thermal switch causes the CEC to engage (closed) during cold engine operation to speed initial engine warm-up. It closes again under near engine overheat conditions to trigger the CEC to boost curb idle and pull more air through the radiator (summer driving in bumper to bumper traffic).
Techinically, there is no 'TCS' (transmission controlled spark) in 1971 as the system is properly called in '70 and '72. It's called a CEC system for the one year it was used in 1971....Comment
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