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Temperature Sender location questions
#1
Hey ya'll so after pulling the heads off my 351C to put new set of head gaskets I decided to replace all the other gaskets and senders as well. I ended up stripping the eff out of my temp sender. So I had to drill it out. Now I am trying to find the best possible alternative. After some research I have read a 351M code water neck has the provision for a temp sender, I have also read that the second port on the water pump can be used. Can anyone give me some more insight in this? I guess I could tap the hole where the original sender is located but I was hoping to just use a pipe plug and plug the hole and install it is a part that is more easily replaceable.

[Image: 20200216-152119.jpg]

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#2
The port on the 351M or 429 water neck only receives heated water temperature when the thermostat opens. The port on the water pump will show the temperature of the coolant after it passes through the radiator, also after the thermostat opens, although it circulates some coolant through the bypass and block before the thermostat opens.

The only place that shows an accurate temperature all of the time is the threaded opening in the block.

If you use the correct thread sealant you shouldn't have a problem removing the temperature sensor next time. Do not use Teflon tape, it may insulate the threads on the sensor, it has to be electrically grounded so it passes voltage through the sensor to ground. You also need to use the correct tool to remove it, a socket or the closed end of an end wrench, no adjustable (crescent) wrenches.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
I see. So the 351M or water pump port are not accurate enough? I did use a socket. It was just so seized on there. The previous owner of the car put a ton of teflon tape on the sender. It was almost comical how much tape was on there.

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#4
(02-29-2020, 11:16 AM)Heardatbeat Wrote: I see. So the 351M or water pump port are not accurate enough? I did use a socket. It was just so seized on there. The previous owner of the car put a ton of teflon tape on the sender. It was almost comical how much tape was on there.
First off, I'm not sure which motor you're talking about. A 351 M code i.e. 71 351 4V, or a 74 351M engine. Two totally different animals.

Here is a pic of my 351 M code. I actually have two temp senders installed as I added gauges and also kept the original idiot lights operational. The red arrow is the CORRECT location for the sender, in my case the mechanical gauge. The yellow arrow is where I chose to remove the 3 port vacuum temp switch for the dual diaphragm distributor and install the idiot light temp sender. I know this temp will be off slightly, but it's there just because I wanted to keep the light working.

[Image: IMG-0438-LI.jpg]

Geoff.
 I learn something new every day!
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#5
(02-29-2020, 12:22 PM)Stanglover Wrote:
(02-29-2020, 11:16 AM)Heardatbeat Wrote: I see. So the 351M or water pump port are not accurate enough? I did use a socket. It was just so seized on there. The previous owner of the car put a ton of teflon tape on the sender. It was almost comical how much tape was on there.
First off, I'm not sure which motor you're talking about. A 351 M code i.e. 71 351 4V, or a 74 351M engine. Two totally different animals.

Here is a pic of my 351 M code. I actually have two temp senders installed as I added gauges and also kept the original idiot lights operational. The red arrow is the CORRECT location for the sender, in my case the mechanical gauge. The yellow arrow is where I chose to remove the 3 port vacuum temp switch for the dual diaphragm distributor and install the idiot light temp sender. I know this temp will be off slightly, but it's there just because I wanted to keep the light working.

[Image: IMG-0438-LI.jpg]
Sorry! Mine is a 351C M code. So the factory hole is the one where I stripped the threads pretty badly. I don't mind if it's off slightly. But I wanted to plug the original hole with a pipe plug. The one you point at with the yellow arrow is that coming off the water pump? Or is that the one where the heater hose goes?

If you ain't learning, you ain't living. 
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#6
If a pipe plug will seal, there's no reason a new temperature sensor won't seal. I would get a tap and clean the threads first, whether you use a pipe plug or the sensor in the block hole.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#7
(02-29-2020, 12:35 PM)Don C Wrote: If a pipe plug will seal, there's no reason a new temperature sensor won't seal. I would get a tap and clean the threads first, whether you use a pipe plug or the sensor in the block hole.
You are right. I think I am overthinking things. Worst case is I will have to tap it to 1/2 inch npt and use a bushing to bring back down to 3/8 npt so I can use the stock sender in the stock location.

If you ain't learning, you ain't living. 
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#8
(02-29-2020, 12:32 PM)Heardatbeat Wrote:
(02-29-2020, 12:22 PM)Stanglover Wrote:
(02-29-2020, 11:16 AM)Heardatbeat Wrote: I see. So the 351M or water pump port are not accurate enough? I did use a socket. It was just so seized on there. The previous owner of the car put a ton of teflon tape on the sender. It was almost comical how much tape was on there.
First off, I'm not sure which motor you're talking about. A 351 M code i.e. 71 351 4V, or a 74 351M engine. Two totally different animals.

Here is a pic of my 351 M code. I actually have two temp senders installed as I added gauges and also kept the original idiot lights operational. The red arrow is the CORRECT location for the sender, in my case the mechanical gauge. The yellow arrow is where I chose to remove the 3 port vacuum temp switch for the dual diaphragm distributor and install the idiot light temp sender. I know this temp will be off slightly, but it's there just because I wanted to keep the light working.

[Image: IMG-0438-LI.jpg]
Sorry! Mine is a 351C M code. So the factory hole is the one where I stripped the threads pretty badly. I don't mind if it's off slightly. But I wanted to plug the original hole with a pipe plug. The one you point at with the yellow arrow is that coming off the water pump? Or is that the one where the heater hose goes?
 It's off the water pump housing. The M code ought to have the three port v switch for the dual diaphragm distributor unless it's been removed by someone else. Unable to find the pic of that, sorry

Geoff.
 I learn something new every day!
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#9
(02-29-2020, 01:08 PM)Stanglover Wrote:
(02-29-2020, 12:32 PM)Heardatbeat Wrote:
(02-29-2020, 12:22 PM)Stanglover Wrote: First off, I'm not sure which motor you're talking about. A 351 M code i.e. 71 351 4V, or a 74 351M engine. Two totally different animals.

Here is a pic of my 351 M code. I actually have two temp senders installed as I added gauges and also kept the original idiot lights operational. The red arrow is the CORRECT location for the sender, in my case the mechanical gauge. The yellow arrow is where I chose to remove the 3 port vacuum temp switch for the dual diaphragm distributor and install the idiot light temp sender. I know this temp will be off slightly, but it's there just because I wanted to keep the light working.

[Image: IMG-0438-LI.jpg]
Sorry! Mine is a 351C M code. So the factory hole is the one where I stripped the threads pretty badly. I don't mind if it's off slightly. But I wanted to plug the original hole with a pipe plug. The one you point at with the yellow arrow is that coming off the water pump? Or is that the one where the heater hose goes?
 It's off the water pump housing. The M code ought to have the three port v switch for the dual diaphragm distributor unless it's been removed by someone else. Unable to find the pic of that, sorry
So be clear, you have it running off of this one? If so how off is it? I think that would be a good choice for relocating it.
[Image: 51-Ul-Ul-Jnd-EL-AC-SX466-2.jpg]

If you ain't learning, you ain't living. 
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#10
(02-29-2020, 01:56 PM)Heardatbeat Wrote: So be clear, you have it running off of this one? If so how off is it? I think that would be a good choice for relocating it.
[Image: 51-Ul-Ul-Jnd-EL-AC-SX466-2.jpg]
Temperature wise, no idea really, may be 10-20 degrees. I would definitely try to re-tap the proper port. You have to block it off regardless, so you might as well use it for the intended purpose. This of course is a pipe thread, make sure you don't go too deep with the tap or you might have more issues trying to seal it and as Don C said, use the paste type, not Teflon tape.
I just decided to use the pump port for the idiot light sender as I no longer need nor use the three port vac switch.
Don't overthink this, but please make sure that the sender you buy is for the system you're using, gauge or idiot light, they are different.

Geoff.
 I learn something new every day!
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