2 Temperature Sending units?

[Zonaman]

I've always been a little confused about how my small block 350 has 2 temperature sending units- one over the thermostat housing and one driver's side head. I'm currently reading off the Thermostat housing. Is there a best location (using standard factory gauge)? Is there any advantage to adding a second gauge that perhaps reads in degrees F?

Thanks.

[72SB]

If you have a factory gauge (original to the truck) than the sending unit wired to it should be right

Vehicles with just a dash light for temp the sender is typically on intake manifold or sometimes T Stat housing. For a "gauge" it would be head, where temp is more accurate IMHO (generally will read 10 degrees hotter than one on manifold)

[leftybass209]

The heads are the biggest issue if you start to overheat, so I'll never quite understand checking the temp in the thermostat housing or manifold.

[dmjlambert]

Some people have a sending unit for the gauge in the cab, and another sending unit that turns electric fan at the radiator on and off as needed. That may be why you have 2 sending units. There is probably a threaded hole in each head, so both of the sending units can go in the heads if desired. I have a sending unit on the driver side head for the gauge, and a sending unit on the passenger side head that I have yet to wire up that will go to the TEMP warning light. They are different types of sending units, one gives a variable resistance to ground to work the gauge, and the one for the warning light switches on at 240 +/- 10 degrees.

[geezer#99]

Early 283 had the factory sensor on the intake near to the thermo housing.
1968 was the first year for sensor in head.

[dagnabbitt]

I have two thermostat sending units and two gauges. Previous owner, rather than mess with the factory gauges and sending unit, added a second one for under the dash that is a little easier to read (ie it has numbers on it).

[Steeveedee]

^ I did this because my in-dash temp gauge was going bug nuts. At some point that will be fixed. I priced a complete dash from Autometer. O.o

[MARKDTN]

I may be wrong, but the temperature sending unit for gauge (or light) was always in the intake and then the head. There could be a ported vacuum switch in the T-stat housing, but I don't believe the gauge sender was ever there from the factory.

[Zonaman]

I meant to follow up on this a while back. So if I want a second guage reading off the head, one with numbers on it, what temperature range should be on the guage and is there one that will work with the existing sender?

Thanks