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Old 06-15-2010, 07:46 PM
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Coolant Sensor on 75 Pontiac 400?

Can some one tell me where the coolant sensor is located on a 75 Pontiac 400 with HEI? I read some where they are placed on the driver's side engine head and this head tends to run hotter than the passenger side.

Today I installed a mechanical water temperature gauge on the engine. I removed what I think is the coolant sensor. It's located on the driver's side head and has two wires connected to it. The wires are in a harness so I couldn't trace them down to where they go. I wrapped the wire connectors in tape and left them hanging.

I get the water gauge sending unit in, fill the radiator and start the engine. The engine didn't want to start but finally took off and idled slower than normal next I head a deafening back fire with could of smoke out the tail pipe. A few seconds go by and another back fire. It sounded like a shotgun or 3006 going off and echoed off the houses in the block. I quickly shut the engine down.

I am not sure if that was the coolant sensor I removed but it affected the engine. So what did I remove and how could it affect the engine? I plan on re-installing what ever it's called that I removed.

So where am I supposed to connect the water gauge sending unit?

Any ideas welcome.



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Old 06-15-2010, 09:03 PM
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Coolant temp sender (aka sensor) for a gage-equipped 1975 Pontiac 400:

Pre-1975 sender looks like:

Disconnecting this will not cause the engine to run any different, possibly the wires getting moved around caused other wiring problems.

The sender will be located in the cylinder head or in the intake front water crossover.
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Old 06-16-2010, 11:42 AM
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Thanks for the input and I will check the wiring over.

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