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Old 05-03-2009, 10:17 PM   #1
70LonghornCST
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Temperature Sending Unit

I recently purchased a new temperature sending unit and it was too big. I need one that has the flat head so I can connect my harness wire to it. My old one only had threads and a small nut. I don't want to cut the wire and crimp on a circular terminal. I want it to look stock with the plastic end that slips over the flat head. The one I purchased was advertised on eBay as "Temperature Sender 1967 68 69 70 71 72 Chevy/GMC Truck"

But when I pulled my old one out, it was much smaller. The new one required a 15/16" socket, while the old required a 3/4" socket. I pulled it from the side of the block on the driver side.

The engine is a replacement 350 crate engine from a GM dealer.

Help! Are there different sized temp sending units for a 350?
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Old 05-04-2009, 01:28 AM   #2
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Re: Temperature Sending Unit

ttt
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Old 05-04-2009, 01:44 AM   #3
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Re: Temperature Sending Unit

Photos of the one you have on hand, and the one you want?

The one I got from Napa? was about he size of a half dollar coin, with a nail-head-like terminal. I just cut the plastic cover off the female end of regular connector and slid it over the end. Works for me, just a driver.
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Old 05-04-2009, 01:48 AM   #4
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Re: Temperature Sending Unit

Scroll down to page 98 or 99.
http://www.scribd.com/full/5722345?a...jcbazlklxtunnw
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Old 05-04-2009, 04:33 PM   #5
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Re: Temperature Sending Unit

My guess is you either have a later model set of heads that requires you to have a 3/8NPT sensor or you have an aftermarket sensor with an adaptor. The correct size is a 1/2npt thread size but if you have late model heads you will need to turn the sensor down on a lathe and rethread it or find a sensor that will work with your gauge. I have yet to find one to work with my gauge.
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Old 05-04-2009, 04:43 PM   #6
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Re: Temperature Sending Unit

Well what does the wrong sensor do to your gauge?

With my older small block, we just ordered one that was designated for the truck. Dunno if the connector is proper, but it works.
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Old 05-04-2009, 04:49 PM   #7
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Re: Temperature Sending Unit

The new 3/8npt sensor will not work with the 67-72 gauge. It will read hot when its not. The ohms are different for later model gauges than ours. What are the casting #'s on your heads. I just went through all this with mine. Im running a set of 99 model vortec heads. I had to have someone turn my sensor down and rethread it. I havent had a chance to try it out yet though.
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Old 05-04-2009, 08:10 PM   #8
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Re: Temperature Sending Unit

I had the same issue with the newer heads having smaller threads. I ended up drilling and tapping the head 1/2 NPT and using the sensor for our trucks. I had gone to NAPA and they have the ohm listing for all of the sending units but no luck on having the correct ohms in a smaller thread version of the sensors.

I believe the range needed in order for the sending unit to work with the truck gauges is in the 80 to 900 ohm range, (80 ohms being hot and 900 being cold).

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Old 05-04-2009, 10:03 PM   #9
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Re: Temperature Sending Unit

Quote:
Originally Posted by monte0185 View Post
The new 3/8npt sensor will not work with the 67-72 gauge. It will read hot when its not. The ohms are different for later model gauges than ours. What are the casting #'s on your heads. I just went through all this with mine. Im running a set of 99 model vortec heads. I had to have someone turn my sensor down and rethread it. I havent had a chance to try it out yet though.
Wouldn't an easier mod be tossing on a resister in series to correct for the difference in Ohms? Similar to the changes some make to correct for their fuel guages with different sending units.

I would imagine that being far easier/cheaper than having to have the sensors machined.
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Old 05-05-2009, 08:27 AM   #10
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Re: Temperature Sending Unit

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Wouldn't an easier mod be tossing on a resister in series to correct for the difference in Ohms? Similar to the changes some make to correct for their fuel guages with different sending units.

I would imagine that being far easier/cheaper than having to have the sensors machined.
If it could be done I would completely be up for that. I think the problem with that is the newer sensors are backwards from the older ones. I dont think you can correct this with an inline resistor. I could however be wrong though.
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Old 05-05-2009, 11:14 AM   #11
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Re: Temperature Sending Unit

I put my temp sending unit on my intake manifold and it works just fine. Is that an option ? My engine is a 350HO crate engine with Vortec Heads. I had to crimp on a not so stock looking terminal, but I'm sure you can find a stock looking one or somehow take the black plastic cover to the old one and get it to cover up the ugly terminal ?
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Old 05-05-2009, 04:28 PM   #12
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Re: Temperature Sending Unit

The head is a more reliable point to put the sensor. Up top, given if you had a coolant leak, your sensor would no longer be reading the coolant temp, just the hot air. Which could give a false reading saying your cool, when your over heating.
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Old 05-05-2009, 08:56 PM   #13
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Re: Temperature Sending Unit

Thanks for all of the replies. I will 1st double check to see if there is a second port option for a larger sized sensor. If not, I will try some of the suggestions offered. I wonder if a different car maker has an approptiate sized sensor that will work? I know Mopar has a smaller sized sensor, but I am not sure about the OHMS.
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Old 05-05-2009, 09:24 PM   #14
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Re: Temperature Sending Unit

I plugged my head and moved the sending unit to the intake manifold.
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Old 05-05-2009, 10:16 PM   #15
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Re: Temperature Sending Unit

try a sending unit for a set of 90s era heads, mine is the small type like your talking about. i ended up using an aftermarket gauge and mounting in the original location.
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Old 05-05-2009, 09:23 PM   #16
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Re: Temperature Sending Unit

I also have the later heads and I have my sensor in the intake, works just fine.
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Old 05-06-2009, 01:44 AM   #17
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Re: Temperature Sending Unit

Well, I don't have a port for a 1/2 anywhere else on the block, and the stock manifold does not have a plug anywhere I can see.

However, I found this adaptor on ebay (220388003191). What do you think?
It shows as 3/8" NPT male to 1/2" female.
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Old 05-06-2009, 02:25 AM   #18
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Re: Temperature Sending Unit

I have a 350 and mine is tapped for 1/2 NPT. I would be VERY careful with an adapter like that. A brass adapter can act as a heat sink and shift the position of the sensor. The sensor was engineered to be in a specific place and it needs to be there otherwise it will give you inaccurate readings. Not that it is a a bad idea.
Mechanically you could find a brass bushing that would locate the sensor in approximately the correct place.This would be all threads on the outside and inside. Should be able to get one at any plumbing supply house. But make sure it is a bushing NOT an adaptor. then you have the other problem. the output of the sensor. Don't know what to tell you about that. Best of luck. Just my .02.

arrrgh, I just re-read your post. I am sorry. Never mind what I just said about the bushing. Just be careful with the adapter.

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Old 05-06-2009, 09:26 AM   #19
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Re: Temperature Sending Unit

I can machine the stock style sending unit to fit head holes that are 3/8 pipe. Price is 25.00 shipped. This includes a new sending unit that has been modified. I sent one to member monte0185 but he has not installed it yet. PM me if you are interested or have questions.
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Old 05-06-2009, 09:49 AM   #20
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Re: Temperature Sending Unit

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I can machine the stock style sending unit to fit head holes that are 3/8 pipe. Price is 25.00 shipped. This includes a new sending unit that has been modified. I sent one to member monte0185 but he has not installed it yet. PM me if you are interested or have questions.
Looks fantastic by the way!! I was going to install it yesterday while we had a break in the rain but had to mow the yard instead!! Darn house chores anyway.

This is the route I suggest. I have talked to a couple people who have drilled their head out to fit but theres not alot of meat there for new threads At least it was that way on my vortec heads so if not done right you can ruin the head easily.
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Old 06-03-2013, 12:17 PM   #21
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Re: Temperature Sending Unit

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Originally Posted by brian mac View Post
I can machine the stock style sending unit to fit head holes that are 3/8 pipe. Price is 25.00 shipped. This includes a new sending unit that has been modified. I sent one to member monte0185 but he has not installed it yet. PM me if you are interested or have questions.
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Old 05-06-2009, 05:43 PM   #22
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Re: Temperature Sending Unit

Quote:
Originally Posted by brian mac View Post
I can machine the stock style sending unit to fit head holes that are 3/8 pipe. Price is 25.00 shipped. This includes a new sending unit that has been modified. I sent one to member monte0185 but he has not installed it yet. PM me if you are interested or have questions.
Awsome!
PM sent.
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Old 08-04-2014, 12:35 AM   #23
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Re: Temperature Sending Unit

Brian Mac posted that he could turn down and rethread a dual temp sender. I would like to see if he is still around and can do this for me. It is the sender for the hot and cold lights. It is in my 65 chevy impala with a 350 and late model heads and a TPI. He was the only one that had a very good idea. I am also working on a 72 Chevy pickup. Any help ....
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Old 08-04-2014, 11:44 AM   #24
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Re: Temperature Sending Unit

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Originally Posted by Lead Sleader View Post
Brian Mac posted that he could turn down and rethread a dual temp sender. I would like to see if he is still around and can do this for me. It is the sender for the hot and cold lights. It is in my 65 chevy impala with a 350 and late model heads and a TPI. He was the only one that had a very good idea. I am also working on a 72 Chevy pickup. Any help ....
See post 23 in this thread http://67-72chevytrucks.com/vboard/s...d.php?t=627880 for Brian Mac's contact info. You can also send him a PM. However, his last forum activity was July 18, so it may take a few days for a response.

Welcome to the forum!!
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Old 08-04-2014, 12:16 PM   #25
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Re: Temperature Sending Unit

I had mine machined down cause I'm running newer heads. That's the only way it will work so you can use the factory gauge cluster ..
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