Help! Water temp sender dilemma
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Joined: Oct 2008
Posts: 59
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From: Milton Florida
Help! Water temp sender dilemma
Obe-wans of the forum, you're my only hope! I've rebuilt my '75 350 into a 383 stroker with Patriot aluminum heads. The threaded hole in the head is for a 3/8" sender-the original from the chevy heads is 1/2". I'd rather not drill and tap the new heads-Patriot said use a sender from an 89-90 model because that's when GM changed the size. But how do I know if that sender is compatible with the old gauge? 
Anybody have any other suggestions-thanks for the help!
Anybody have any other suggestions-thanks for the help!
Safety Car
Joined: Aug 2001
Posts: 4,883
Likes: 11
From: North Easton Mass
Obe-wans of the forum, you're my only hope! I've rebuilt my '75 350 into a 383 stroker with Patriot aluminum heads. The threaded hole in the head is for a 3/8" sender-the original from the chevy heads is 1/2". I'd rather not drill and tap the new heads-Patriot said use a sender from an 89-90 model because that's when GM changed the size. But how do I know if that sender is compatible with the old gauge? Anybody have any other suggestions-thanks for the help!
Anybody have any other suggestions-thanks for the help!
Rick B.
Burning Brakes
Joined: Mar 1999
Posts: 1,047
Likes: 3
From: CA
I sent my temp gauge to Clocks by Roger along with the sender I wanted to use and he re-calibrated the gauge to make it work with the sender. It was pretty close. When I had to pull my heads again for other reasons, I had the heads taped to the correct size thread to accommodate the original sender. Of course this meant I need to send my gauge back to Roger. I think the easiest solution is to install in the intake or thermostat housing as suggested earlier in this post. Good luck.
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
Obe-wans of the forum, you're my only hope! I've rebuilt my '75 350 into a 383 stroker with Patriot aluminum heads. The threaded hole in the head is for a 3/8" sender-the original from the chevy heads is 1/2". I'd rather not drill and tap the new heads-Patriot said use a sender from an 89-90 model because that's when GM changed the size. But how do I know if that sender is compatible with the old gauge? Anybody have any other suggestions-thanks for the help!
Anybody have any other suggestions-thanks for the help!I am using a GM sender for an 80. It is close, but not right on the money. As others have suggested if you don't want to try that, I'd put the original in the intake.
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Race Director
Joined: Dec 1999
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From: Forked River NJ
Not for a car I did this winter. A crate motor with Vortec heads. I went in circles with this and finally put in my old sensor from an 80 model and it worked. It was not dead on but only varied a few degrees from what it actually was. Close enough.
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
Willcox has the info you need to match the sender to the guage. Look in their help topics.
Here is a clip from Willcox help topic for resistance vs temp.
220 degrees = 70 ohms
200 degrees = 90 ohms
160 degrees = 140 ohms
120 degrees = 250 ohms
100 degrees = 340 ohms
If you use a resistor the guage will only be accurate in one spot. Not the best choice.
If you have the correct sender/guage combo already SAMMAN is correct you can get an adapter. I got mine at O'Reiley's Auto for $12.00 just a few weeks ago. It's an Edelman part number and it wasn't on the shelf. They had to get it from the rack in the back of the store. I have the receipt so if you need the part number let me know.
As mentioned you might also try the pipe threaded plugged hole at the top of the water pump or in the manifold near the thermostat.
BTW...I went to Home Depot, Lowes, hardware stores, other auto parts stores,boating stores, etc and could not find the adapter. I was about to give up and finally found one at O'Reily's once I got the part number from a CF member.
Here is a clip from Willcox help topic for resistance vs temp.
220 degrees = 70 ohms
200 degrees = 90 ohms
160 degrees = 140 ohms
120 degrees = 250 ohms
100 degrees = 340 ohms
If you use a resistor the guage will only be accurate in one spot. Not the best choice.
If you have the correct sender/guage combo already SAMMAN is correct you can get an adapter. I got mine at O'Reiley's Auto for $12.00 just a few weeks ago. It's an Edelman part number and it wasn't on the shelf. They had to get it from the rack in the back of the store. I have the receipt so if you need the part number let me know.
As mentioned you might also try the pipe threaded plugged hole at the top of the water pump or in the manifold near the thermostat.
BTW...I went to Home Depot, Lowes, hardware stores, other auto parts stores,boating stores, etc and could not find the adapter. I was about to give up and finally found one at O'Reily's once I got the part number from a CF member.
Last edited by 08vycpe; May 7, 2010 at 11:31 AM. Reason: added BTW...
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
If you use an adapter, you may not get an accurate reading because you are moving the sensor away from moving water and into a pocket. small sender into big hole, not as big a deal. Big sender into small hole, the tip of the sender will be in a reducer.
Burning Brakes
Joined: Jan 2006
Posts: 957
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From: Burlington wisconsin
I had my original turned down to 3/8" NPT here at work. There is plenty of meat on the original, worked perfect. I tried the reducer bushings, adapters and ones I thought were of the same resistance, nope, all acted funny regarding readings.
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
You are correct. Without the sender in the water stream you don't get an accurate reading but since I know where "normal" is on the guage and I gets lots of needle movement I've got a good idea when the car begins to run hot or hasn't warmed up yet.
Thread Starter
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Joined: Oct 2008
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From: Milton Florida
Many thanks to all who responded-lots of good ideas and great information
! Right now I'm leaning toward turning down the original to 3/8"-that's something I never considered! I have a new thermostat housing that is tapped to 1/2" and I could go that route too. I felt like keeping the sender in the head might be better than the thermostat housing though-but Ive found I can't always trust my logic
With all your help I'm getting on the right track.
! Right now I'm leaning toward turning down the original to 3/8"-that's something I never considered! I have a new thermostat housing that is tapped to 1/2" and I could go that route too. I felt like keeping the sender in the head might be better than the thermostat housing though-but Ive found I can't always trust my logic With all your help I'm getting on the right track.
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Many thanks to all who responded-lots of good ideas and great information! Right now I'm leaning toward turning down the original to 3/8"-that's something I never considered! I have a new thermostat housing that is tapped to 1/2" and I could go that route too. I felt like keeping the sender in the head might be better than the thermostat housing though-but Ive found I can't always trust my logic With all your help I'm getting on the right track.
! Right now I'm leaning toward turning down the original to 3/8"-that's something I never considered! I have a new thermostat housing that is tapped to 1/2" and I could go that route too. I felt like keeping the sender in the head might be better than the thermostat housing though-but Ive found I can't always trust my logic With all your help I'm getting on the right track.
Former Vendor
Joined: Aug 2006
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
08..
I may need to pull those numbers down as a fixed scale. In our testing in late December trying to accomplish a fix for this problem... it pretty much proved this chart to only be accurate with some dash units.
Over the years, the dash unit scale and requirements changed... so what input is accurate for one gauge may not be for another one. Matter of fact.. I think when I get back in town, I'll pull this data down and publish the input readings for the different gauges from 63-82. This would probably help a lot of people in the future.
To me... if the old sending unit was working fine.. then I would either put it in the intake or turn it down to 3/8 npt and go with it. Matching the gauges to the sending unit has been done.. David Howard was the first one we did.. and yes... something went wrong on this one but we have now nailed this down. The problem with this is the expense in doing it.
Willcox
I may need to pull those numbers down as a fixed scale. In our testing in late December trying to accomplish a fix for this problem... it pretty much proved this chart to only be accurate with some dash units.
Over the years, the dash unit scale and requirements changed... so what input is accurate for one gauge may not be for another one. Matter of fact.. I think when I get back in town, I'll pull this data down and publish the input readings for the different gauges from 63-82. This would probably help a lot of people in the future.
To me... if the old sending unit was working fine.. then I would either put it in the intake or turn it down to 3/8 npt and go with it. Matching the gauges to the sending unit has been done.. David Howard was the first one we did.. and yes... something went wrong on this one but we have now nailed this down. The problem with this is the expense in doing it.
Willcox
