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Old 04-27-2013, 09:49 AM   #1
PatrickGMC70
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Temp sensor question

I'm rebuilding my engine and I'm at the point where it's going back together.

It looks like I have two temp sensors in the block - one is the light style and the other is the gauge style. My dash has a temp gauge (I'm not sure if it has a light and can't check at the moment because the truck isn't here)

The manual says that one head has the temp sensor and the other is oil pressure. But I thought my oil pressure was that little line that come out the back of the block near the distributor.

Can anyone clarify this for me? If I'm supposed to have two temp sensors does it matter which one goes in which head?

Thanks,
Patrick

Pic below:



Oh, one other thing, what is this? It was bolted to the intake manifold.


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Old 04-27-2013, 10:03 AM   #2
GASoline71
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Re: Temp sensor question

So you had one of those senders in each head? The factory location for sending units is the drivers side head only. Unless someone ran another temp sending unit in the passenger head to run a thermostat for electric fans. But they both are factory style senders. I'm sure there were some applications that used 2 sending units. But I haven't a clue on that...

I have gauges as well in my '72 GMC and have the one in the top of the pic located in my drivers side cylinder head.

The hunk of metal in your lower pic looks like a part of the "spark knock control" unit from a '72 truck. There should have been a wire harness that went to it. I had that on my truck as well when I bought it. I removed the whole assemply and wire harness toot sweet. I also completely rebuilt the engine and used a Holley carb and Edelbrock intake.

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My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread.

The Rebuild of Creeping Death after the wreck

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I would never rebuild a 305.
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I love using vacuum gauges as part of the carb tuning process. I hook the gauge to the inside of my garbage can and leave it there.
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Remember Murphys 2nd law of mechanical relationships... "OPPOSING COMPONENTS ATTEMPTING TO OCCUPY THE SAME SPACE, AT THE SAME TIME, GENERALLY END UP OCCUPYING ADJOINING SPACE AT THE BOTTOM OF THE OIL PAN"
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Old 04-27-2013, 10:04 AM   #3
rkn463
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Re: Temp sensor question

I'm assuming a small block Chevy ( not that familiar with the big block layout). Anything on the head is water temp, the small hole by the distributor is oil pressure. I'm a fan of the gauge and a light to get attention.

-Richard
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Old 04-27-2013, 12:03 PM   #4
PatrickGMC70
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Re: Temp sensor question

Oh, I guess some details would have helped...

1970 GMC C1500 350, 3OTT. The truck seemed stock, or at least 95% stock.

Driver side hole is near the front of the head (between #1&3) and passenger side hole is near rear of head (between #6$8).
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Old 04-27-2013, 12:24 PM   #5
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Re: Temp sensor question

You should have had either one or the other of those sensors, not both. Top is for a gauge and bottom is for a light.

Oil pressure is like you stated, and should be 1/8" NPT IIRC.
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Old 04-27-2013, 12:32 PM   #6
PatrickGMC70
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Re: Temp sensor question

If I'm only supposed to have 1, what goes in the other hole? The shop manual says oil switch, but as far as I know, there's coolant in those passages, not oil.
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Old 04-27-2013, 12:47 PM   #7
Shyguy
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Re: Temp sensor question

All the older engines I have had only had a plug in the passenger side head. Newer engines sometimes has a sensor in the passenger side head to control an auxilary electric fan.
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Old 04-27-2013, 01:00 PM   #8
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Re: Temp sensor question

Those are part of the TCS system (transmission controlled spark) It only allows vacuum advance when the engine is up to operating temp and in high gear. Temp sender should be in pass side head.
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Old 04-27-2013, 02:20 PM   #9
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Re: Temp sensor question

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All the older engines I have had only had a plug in the passenger side head. Newer engines sometimes has a sensor in the passenger side head to control an auxilary electric fan.
Yup... just a NPT pipe plug. 1/2" I think.

Gary
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My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread.

The Rebuild of Creeping Death after the wreck

Quote:
Originally Posted by LONGHAIR View Post
I would never rebuild a 305.
Quote:
Originally Posted by prostreetC-10 View Post
I love using vacuum gauges as part of the carb tuning process. I hook the gauge to the inside of my garbage can and leave it there.
Quote:
Originally Posted by Marv D View Post
Remember Murphys 2nd law of mechanical relationships... "OPPOSING COMPONENTS ATTEMPTING TO OCCUPY THE SAME SPACE, AT THE SAME TIME, GENERALLY END UP OCCUPYING ADJOINING SPACE AT THE BOTTOM OF THE OIL PAN"
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Old 04-29-2013, 06:56 AM   #10
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Re: Temp sensor question

My 71 C/10 307, 3OTT has 2 senders.
The top one in your pic is correct for the gauge, mounts in drivers side.
I also have a sender in my passenger side head. It was for the TCS, but the rest of that wiring and controls were removed by the PO.
You can just plug the ps with a 1/2" pipe plug. That's also a good location to run an aftermarket mechanical temperature gauge. 2 readings are better than one.
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Old 04-29-2013, 07:27 AM   #11
PatrickGMC70
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Re: Temp sensor question

Thanks everyone. Weird that I had both. I could have sworn there were wires hooked up to both; guess I'll know more when I start putting it back together tonight.
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Old 07-29-2013, 01:24 AM   #12
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Re: Temp sensor question

Reviving an old thread, I know... Does anyone know where to find a new connector/terminal to slide onto the top temp sending unit? I want to replace the wire and the connector but couldn't find one at the parts store. Does a regular female connector that would slide onto a spade work?
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Old 07-29-2013, 05:48 AM   #13
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Re: Temp sensor question

Yes, I believe a regular female crimp connector will work.
You might have to tweak it a little. You may have to spread it open slightly. Pry it with a super skinny screwdriver or pocket knife. Squeeze it with a needle nose pliers if it's too loose. Adjust it for a snug fit over the sender tit before you crimp it on the green temperature wire.
The green temperature sending unit wire is a pretty small gauge, like maybe 18ga. So, you'll need a connector for that size wire. A Red or Blue should do, Yellow will be too big for that wire. Make sure everything fits snug to make a proper connection.
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Old 07-29-2013, 10:20 AM   #14
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Re: Temp sensor question

Here's a link to the connector you need if you want the original type. This place has just about everything you could want related to electrical connectors.

http://www.repairconnector.com/produ...Connector.html
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Old 07-29-2013, 10:42 AM   #15
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Re: Temp sensor question

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Here's a link to the connector you need if you want the original type. This place has just about everything you could want related to electrical connectors.

http://www.repairconnector.com/produ...Connector.html
Thanks for posting. I needed that also!
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