Temperature Sending Units
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 1,164
Likes: 1
From: Port Clinton Ohio
St. Jude Donor '08-'09-'10-'11-'12-'13
Temperature Sending Units
I have a '73 L-48 and am replacing the original engine with a GM crate motor with Vortec heads. Tonight I was pulling parts off of the old motor to put on the new one. I pulled both temp sending units out of the old one and tried to put them in the new motor but the holes are too small in the Vortec heads. Has anyone else run into this problem?
Can a newer style smaller unit be used?
Also, are both sending units needed? One was in the right head near the rear of the engine and has two wires attached. The other was on the left head toward the front and had one wire attached.
Thanks
Can a newer style smaller unit be used?
Also, are both sending units needed? One was in the right head near the rear of the engine and has two wires attached. The other was on the left head toward the front and had one wire attached.
Thanks
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Use an '82 Corvette sending unit for the Vortec head. It'll match with your gauge, but will fit the smaller bore.
For the passenger side, that's a switch, not a sender. It has something to do with the distributor advance for 3rd and 4th in manual cars.
Most people remove it and just plug the hole.
For the passenger side, that's a switch, not a sender. It has something to do with the distributor advance for 3rd and 4th in manual cars.
Most people remove it and just plug the hole.
Race Director
Joined: Apr 2003
Posts: 19,351
Likes: 654
From: Tampa, Florida
Use an '82 Corvette sending unit for the Vortec head. It'll match with your gauge, but will fit the smaller bore.
For the passenger side, that's a switch, not a sender. It has something to do with the distributor advance for 3rd and 4th in manual cars.
Most people remove it and just plug the hole.
For the passenger side, that's a switch, not a sender. It has something to do with the distributor advance for 3rd and 4th in manual cars.
Most people remove it and just plug the hole.
Instructor
Joined: Jul 2003
Posts: 210
Likes: 0
From: eaton rapids mi
I recently switched to a gm crate with vortec heads and used the 82 temp sender. The problem i had is the gauge reads much higher than it did with the correct temp sender. On the stock setup when the gauge was just above 200 i had the fans kick on. On the new setup they would not kick on until the gauge was past straight up/down (whatever temp that is suppose to read). Since i have electric fans with an electronically controlled on/off independent of the sensor i was able to calibrate the gauge to read the same it was prior to the engine change. Easy to do using a 100 ohm trim pot in line with sender. For me this translated to 24 ohms.
Burning Brakes
Joined: Mar 1999
Posts: 1,047
Likes: 3
From: CA
I could not find a temp sending unit with the smaller threads that gave an accurate reading. I ended up sending my temp gauge to Rogers clock repair and he calibrated to work with a smaller thread sending unit.
http://www.corvetteclocks.com/
http://www.corvetteclocks.com/
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
I could not find a temp sending unit with the smaller threads that gave an accurate reading. I ended up sending my temp gauge to Rogers clock repair and he calibrated to work with a smaller thread sending unit.
http://www.corvetteclocks.com/
http://www.corvetteclocks.com/
That is so odd. Do the gauges in the older C3s differ that much from the newer ones? The temp readings are the same from '77 thru '82.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Yes. I think the resistance values on sending units were different and recalibration is required to get an 'old' gauge and a 'new' sending unit to read correctly. Test the old and new sending units by measuring their resistance at room temperature and then again with boiling water just removed from heat. If they are close to the same, it should work OK; if not, you will need the correct value resistor in the circuit to recalibrate it.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
I had the same problem when I built my new engine with C4 aluminum heads. I was unable to locate a smaller sending unit to fit the head, with the same electrical characteristics as the stock sending unit. So I mounted the sending unit in one of the holes in the intake manifold and ran a black jumper from the original temp. wire around the engine compartment and forward to the new sending location, concealing the wire as I went. I use a 195° (stock) thermostat; the gauge reads the same as it did with the sending unit in the original location in the original engine.
I've read threads where others claim the coolant temp will be different in the heads and the intake manifold. In my experience it is the same. When you think about it, the coolant is moving pretty fast through the engine and the new location up near the thermostat isn't very far from the old location in the front part of the head.
As a bonus, if I or a future owner ever wants to reinstall the original engine, the gauge will give the correct temp.
Cheers,
Pete
I've read threads where others claim the coolant temp will be different in the heads and the intake manifold. In my experience it is the same. When you think about it, the coolant is moving pretty fast through the engine and the new location up near the thermostat isn't very far from the old location in the front part of the head.
As a bonus, if I or a future owner ever wants to reinstall the original engine, the gauge will give the correct temp.
Cheers,
Pete
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Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Yes. I think the resistance values on sending units were different and recalibration is required to get an 'old' gauge and a 'new' sending unit to read correctly. Test the old and new sending units by measuring their resistance at room temperature and then again with boiling water just removed from heat. If they are close to the same, it should work OK; if not, you will need the correct value resistor in the circuit to recalibrate it.
In that case, for the older gauges, wouldn't it be easier to drill and tap the existing hole larger to fit the stock sender?
Burning Brakes
Joined: Mar 1999
Posts: 1,047
Likes: 3
From: CA
Difficult to do once the motor is installed as there is not enough room to get a drill in the correct position. I found it easier to pull the temp gauge.
