Looking for thread on modifying 67-72 temp sender

[BigRed76]

I saw a thread a while back about taking an OEM temp sender for 67-72's and milling it down to 12x1.5 threads to fit into the cyl. head of an LS. I tried milling down an OEM 67-72 temp sender but there isn't enough material to get it down small enough for 12x1.5 threads. I've spent hours trying to find that thread and have been unsuccessful, so I'm curious has anyone else successfully done this? Is there another OEM GM temp sender that it smaller and can be milled down for 12x1.5 threads? I've tried some aftermarket temp senders and they don't work, and drilling & tapping the head isn't an option since the engine is in the truck.

[ztk123]

I bought an adapter from street & performance. It threader in to the head on passenger side and allowed for a GM mechanical sender.
Mike

[mongocanfly]

I bought the autometer ls sending unit adapter kit for mine

[dec010974]

I did the same thing as mongocanfly.

[MikeB]

Many years ago I had to use a smaller sender to fit the smaller NPT hole (3/8"?) in a aftermarket head. The sender's resistance values were different than what the 1969 OE gauge was designed for, so I ended up changing the resistor value in the picture below.

What you need to know is:
--The LS1 sender's resistance at, let's say, 100 degrees and 212 degrees. (Do this in a pan of water on a cooktop using an ohmmeter and accurate thermometer).
--The original sender's resistance at those temps.
--The value in ohms of the OE resistor on the back of the gauge.

Get me those numbers and I can probably get you in the ballpark.

I fined tuned mine on the cooktop, and ended up with 180 causing the needle to point straight up. For an LS, you may want 210 to be straight up. My gauge had no numbers on it, just L and H, as I recall.

BTW, I used s standard precision resistor I got from radio shack. It doesn't look like the factory resistor, but it doesn't matter.

[MalibuSSwagon]

This is what you are looking for.

http://www.impalassforum.com/vBullet...d.php?t=273845

You don't need a lathe, just a drill, a flat file and a vice. What I did was chucked up the probe end of the sensor in the drill, clamp the flat file straight up in the vice, and go at it. It's brass so it'll cut easy, but it does take a while. Once you get it down to size, thread the dye down on it, it'll go easy because it's brass, just use some MM oil or whatever, I used jack oil cuz it was handy.

12mm dye is cheap on ebay, I also bought some 12mm copper washers on ebay to seal it like OEM.

[LockDoc]

Originally Posted by BigRed76

I saw a thread a while back about taking an OEM temp sender for 67-72's and milling it down to 12x1.5 threads to fit into the cyl. head of an LS. I tried milling down an OEM 67-72 temp sender but there isn't enough material to get it down small enough for 12x1.5 threads. I've spent hours trying to find that thread and have been unsuccessful, so I'm curious has anyone else successfully done this? Is there another OEM GM temp sender that it smaller and can be milled down for 12x1.5 threads? I've tried some aftermarket temp senders and they don't work, and drilling & tapping the head isn't an option since the engine is in the truck.

There are two sensors, one for idiot lights and one for gauges. The one for gauges is beefier and you can turn it down. The one for the lights can't be turned. When you turn it down do not turn it all the way up to the hex, you have to stay back 1/4" or so. That is where it is thinner and you will weaken it and it will break apart when it is tightened up. It should also be turned on a taper since NPT are tapered. That will also leave more meat toward the top. It does not have to screw into the head all the way. You only have to have it screwed in about half way so go easy when you thread it too.

LockDoc

[BigRed76]

The auto meter sender that most people use, the same one I'm currently using, puts the temp needle at the first mark on the left with the engine at 200, and the gauge barely moves up at all if the engine temp gets up to 220.

The issue I ran into with turning down the oem sender is that even the probe part of the sender is a bigger diameter than the 12x1.5, and when you try to turn down the probe part of the sender there is barely any material there and you can't make it small enough.

One option that I started looking into was finding a sender with the correct ohms range to match the oem sender, but with a 1/4 or 3/8 npt thread, because the probe on those senders are quite a bit smaller and the threaded section would be easier to turn down.

[68c10airstream]

I like what mikeB said. when I did my ls install I drilled the face of my 2001 waterpump and installed the stock sender. Only issue then was when the ls was at full operating temp (say 200 degrees) my stock gauge read 3/4 scale. I fixed that by installing a variable resistor and dialed the gauge back to 1/2 scale by adding additional resistance. When I was satisfied I removed the inline variable resistor and read the value, which was in my case 4 ohms resistance. Went to radio shack and bought a 4 ohm 1/2 watt resistor and permanently soldered it in.

Remember that the sender nail head needs to be shiny like new and all connections clean. This mod has worked flawlessly for years now

[MalibuSSwagon]

With the stock sender installed in the passenger side head, my stock gauge reads straight up at 210 when the engine is at operating temp.

[solidaxel]

Originally Posted by MalibuSSwagon

With the stock sender installed in the passenger side head, my stock gauge reads straight up at 210 when the engine is at operating temp.

Are you using a additional stock sender from the drivers side of a LS engine and placing it in the pass. side and using that for the analog gauge?

[BigRed76]

Originally Posted by MalibuSSwagon

This is what you are looking for.

http://www.impalassforum.com/vBullet...d.php?t=273845

You don't need a lathe, just a drill, a flat file and a vice. What I did was chucked up the probe end of the sensor in the drill, clamp the flat file straight up in the vice, and go at it. It's brass so it'll cut easy, but it does take a while. Once you get it down to size, thread the dye down on it, it'll go easy because it's brass, just use some MM oil or whatever, I used jack oil cuz it was handy.

12mm dye is cheap on ebay, I also bought some 12mm copper washers on ebay to seal it like OEM.

That particular temp sensor won't work with a stock 67-72 temp gauge because the ohms range is much different.