71 temp sending unit

[Mike H.]

I am sure this topic has been beat to death, but as I am new here I have not been able to successfuly search the archives for the info I need. I have seen posts, regarding older models, giving Wells TU5 as a sending unit that will work. Will it work with my '71 BB? The gauge reads 225 my info-red shows the temp to be 180-190. I am not after getting the exact temp reading on the gauge, I would just like to have a little more room to indicate potential problems. Thanks in advance.
PS. Head temp near sending unit reads 205 hoses and radiator 180.

[Ed Jennings]

Re: 71 temp sending unit

I'm not sure about the resistance of the 71 and how it compares to the older cars. You could go to Autozone and ask for a temp sender for a 71 and see what they give you.

Your IR gun is reading 205 at the sender. Since the sender is real close to the exhaust manifold, you may be picking up some heat from there. Assuming of course that you have the sender in the head. Try reading at the base of the thermostat. Hold the gun close enough that the area it's reading is pretty small, like 1" or so. If you get the same readings there or close to what the hose bottoms are, then that is close to your coolant temp.

[Ed Jennings]

Re: 71 temp sending unit

I'm not sure about the resistance of the 71 and how it compares to the older cars. You could go to Autozone and ask for a temp sender for a 71 and see what they give you.

Your IR gun is reading 205 at the sender. Since the sender is real close to the exhaust manifold, you may be picking up some heat from there. Assuming of course that you have the sender in the head. Try reading at the base of the thermostat. Hold the gun close enough that the area it's reading is pretty small, like 1" or so. If you get the same readings there or close to what the hose bottoms are, then that is close to your coolant temp.

[Mike H.]

Re: 71 temp sending unit

Autozone shows no sender required for a '71!!!!! The outlet temp at the thermostat housing shows 180. Yes the sender is in the head and I probably am picking up some exhaust temp from the head casting. Woudn't the sender be calibrated to account for some of this?
Newbie Mike

[Mike H.]

Re: 71 temp sending unit

Autozone shows no sender required for a '71!!!!! The outlet temp at the thermostat housing shows 180. Yes the sender is in the head and I probably am picking up some exhaust temp from the head casting. Woudn't the sender be calibrated to account for some of this?
Newbie Mike

[Ed Jennings]

Re: 71 temp sending unit

Mike, the sender should only pick up the temp from the water. The IR gun, on the other hand is probably getting some of the exhaust heat. The 180 you are getting at the thermostat is likely a better indication of your true coolant temp. I haven't owned a shark since the 70's so I am out of my realm on recommending a sender. I know the Wells TU5 works on C1's and I THINK some folks have successfully used it on C2's as well. Whether the C3 has a similar resistance profile would only be a guess. The TU5 costs $6, and takes about 10 minuets to change. Maybe someone with a little more knowledge will jump in here, but if not, it might be worth a try. Wish I could be of more assistance.

[Ed Jennings]

Re: 71 temp sending unit

Mike, the sender should only pick up the temp from the water. The IR gun, on the other hand is probably getting some of the exhaust heat. The 180 you are getting at the thermostat is likely a better indication of your true coolant temp. I haven't owned a shark since the 70's so I am out of my realm on recommending a sender. I know the Wells TU5 works on C1's and I THINK some folks have successfully used it on C2's as well. Whether the C3 has a similar resistance profile would only be a guess. The TU5 costs $6, and takes about 10 minuets to change. Maybe someone with a little more knowledge will jump in here, but if not, it might be worth a try. Wish I could be of more assistance.

[Jack H.]

Re: 71 temp sending unit

Properly installed temp sender WILL ignore exhaust mani radiation because the 'pellet' that acts as transducer is inside the barrel that enters the water jacket at the outside end and is dominated by coolant circulation. The external body where the connector clips on is electrical only and insulated with the bakelite dielectric.

Remember, original '71 temp senders had the 'needle' contact head (last year for this style) instead of the earlier/later period 'button' head post. So, unless the car's original connector has been changed, replacement temp senders won't hook up to factory stock connector on the wiring....

GM's solution was to chop, discard, and replace the wiring harness' connector with earlier/later style designed to grab the sender's button head....

On original post (gauge reading high vs. measured outlet coolant temp), this isn't unusual. Sorting temp senders to find one with modestly lower room temp static resistance compared to what's currently being used will remedy.

[Jack H.]

Re: 71 temp sending unit

Properly installed temp sender WILL ignore exhaust mani radiation because the 'pellet' that acts as transducer is inside the barrel that enters the water jacket at the outside end and is dominated by coolant circulation. The external body where the connector clips on is electrical only and insulated with the bakelite dielectric.

Remember, original '71 temp senders had the 'needle' contact head (last year for this style) instead of the earlier/later period 'button' head post. So, unless the car's original connector has been changed, replacement temp senders won't hook up to factory stock connector on the wiring....

GM's solution was to chop, discard, and replace the wiring harness' connector with earlier/later style designed to grab the sender's button head....

On original post (gauge reading high vs. measured outlet coolant temp), this isn't unusual. Sorting temp senders to find one with modestly lower room temp static resistance compared to what's currently being used will remedy.

[Jack H.]

Add-on

If current temp sender actually is the factory original 'pin head' or 'needle head' style, the only game in town other than walking umpteen scrap yards and trying to find an original from the era that hasn't been replaced, is to visit Lectric Ltd's web site and buy the special run parts they offer....

[Jack H.]

Add-on

If current temp sender actually is the factory original 'pin head' or 'needle head' style, the only game in town other than walking umpteen scrap yards and trying to find an original from the era that hasn't been replaced, is to visit Lectric Ltd's web site and buy the special run parts they offer....

[Joe L.]

Re: 71 temp sending unit

Mike-----

All Corvette temp senders used in PRODUCTION from 1956 through 1978 are functionally interchangeable. The calibration on all is, for all practical purposes, the same. The only difference in these senders is the terminal type. 1956 used a pin terminal. 1957-67 used a button terminal. 1968 through about 1972 used a pin terminal. Then, from about 1973 until 1978 it was back to button terminal again.

The following senders WILL work and be calibrated properly for your 1971 gauge:

1) GM #6400759---this is a pin type terminal unit and is the one originally used on your car. It is VERY difficult to find in NOS form, though.

2) GM #1513321---this is a button type terminal unit. It will work on your car if your terminal connector is changed (if it hasn't already been changed to the connector for button terminals). The calibration for this unit is correct for your gauge. It is discontinued, but not all that difficult to find NOS;

The current GM replacement sender, GM #12334869, is the unit which I'm told often gives problems with calibration.

One thing to keep in mind, here, though: NO thread sealer or Teflon tape can be used on the threads of the temp sender brass fitting. The temp sender uses a single pin connector and grounds through the brass fitting-to-cylinder head contact. Using any sealer will interfere with the ground and cause inaccurate or erratic temp readings.

[Joe L.]

Re: 71 temp sending unit

Mike-----

All Corvette temp senders used in PRODUCTION from 1956 through 1978 are functionally interchangeable. The calibration on all is, for all practical purposes, the same. The only difference in these senders is the terminal type. 1956 used a pin terminal. 1957-67 used a button terminal. 1968 through about 1972 used a pin terminal. Then, from about 1973 until 1978 it was back to button terminal again.

The following senders WILL work and be calibrated properly for your 1971 gauge:

1) GM #6400759---this is a pin type terminal unit and is the one originally used on your car. It is VERY difficult to find in NOS form, though.

2) GM #1513321---this is a button type terminal unit. It will work on your car if your terminal connector is changed (if it hasn't already been changed to the connector for button terminals). The calibration for this unit is correct for your gauge. It is discontinued, but not all that difficult to find NOS;

The current GM replacement sender, GM #12334869, is the unit which I'm told often gives problems with calibration.

One thing to keep in mind, here, though: NO thread sealer or Teflon tape can be used on the threads of the temp sender brass fitting. The temp sender uses a single pin connector and grounds through the brass fitting-to-cylinder head contact. Using any sealer will interfere with the ground and cause inaccurate or erratic temp readings.

[Ed Jennings]

Re: 71 temp sending unit

Well, given that information, the Wells TU 5 will work on yoour car. There is the issue of the connector. The Wells unit is the flat type, vs the pin type you may or may not currently have. Autozone is not known for the skill of their counter help. Call and ask for the part by part number if you want to try one. It will do until you can find the proper GM unit.

[Ed Jennings]

Re: 71 temp sending unit

Well, given that information, the Wells TU 5 will work on yoour car. There is the issue of the connector. The Wells unit is the flat type, vs the pin type you may or may not currently have. Autozone is not known for the skill of their counter help. Call and ask for the part by part number if you want to try one. It will do until you can find the proper GM unit.