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Old 02-07-2018, 03:48 PM   #1
Macdaddy1
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Join Date: Dec 2017
Location: Niceville Florida
Posts: 241
Water temp sensor

I have a 327 in my 65c10 which is still in build mode. I want to replace the water temp sending unit in the block. My question is there a wire that runs from the sensor to the back of the dash temp gauge? I went down to the parts store and they sold be a Bosch temp gauge. i could not remove the end that attached into the gauge to see if it would fit into the back of my console. I am not sure how the water temp sensor was originally attache. Any help or insight would be appreciated.
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Old 02-07-2018, 04:15 PM   #2
ray_mcavoy
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Join Date: Nov 2009
Location: Sherman, ME
Posts: 1,998
Re: Water temp sensor

The optional factory gauge cluster in these trucks uses an electric temperature gauge. A single wire (typically dark green) runs from the instrument cluster, out through the firewall bulkhead connector, and through the engine wiring harness, to where it plugs into the temperature sending unit on the engine. The standard warning light cluster contains "hot" and "cold" lights instead of an actual temperature gauge. It uses 2 wires (typically light & dark green), one for each light. The wires follow a similar routing and plug into a 2-terminal temperature switch on the engine.

The Bosch gauge you purchased sounds like it is a mechanical temperature gauge. That design has a bulb that fits into the engine and is permanently attached to the gauge via a capillary tube. Removing it will ruin the gauge. Installing this type of gauge requires drilling a hole through the firewall that is large enough for the bulb (and attached nut) to pass through. And there should (hopefully) be a rubber grommet included with the gauge to seal up the hole and prevent the capillary tube from chafing on the edge. Also be sure to route the tube away from any other sharp edges, moving parts, hot exhaust, etc.
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Old 02-08-2018, 12:14 AM   #3
Macdaddy1
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Re: Water temp sensor

I am overwhelmed and the expertise and kindness from people on this board. Thank you for that explanation.
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Old 02-08-2018, 10:00 AM   #4
Dead Parrot
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Join Date: Aug 2012
Location: Oklahoma City, OK
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Re: Water temp sensor

Be aware that matching an electrical temp sensor to the gauge can be a mystical art. The sensor/sender changes resistance to reflect the temp to the gauge(higher temp = lower resistance). GM has used several different resistance curves over the years. If that engine is original to the truck, best bet is keep the sender and hope is still works. For the most part, GM no longer makes sender units for the older stuff and the 3rd party units rarely match the OEM resistance/temp curves.

If the motor is a transplant, decent chance that what you have is an idiot light sender which is basically a switch that closes when the motor temp is too hot.

I had a 68 Impala with a 327 that had a 1 wire idiot light sender.

I would remove and reinstall with new sealant your existing sender while the motor is out. If it proves bad/wrong, much easier to replace without having to fight possibly 50 years of being stuck.
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