Temperature sending unit for gauge location??

[Butchcub]

I have a 1981 SX/4 with a Pontiac 151 and 4 speed. My temp gauge only moves from C to the beginning line. In the past with other car its usually been the sensor. So I bought a new one (single tab) but one problem,, Where is it?
Ive read on the back on the intake manifold. Ive been on and under the car with a light and so has my friend and we cant find it. The only thing I found was something right above the oil pan (passenger side of engine under intake) with three wires going to it.
Any help?

[greymarooneightytwo]

I thought mine was broken for the longest time because it acts exactly the same.. but I wonder now because I have actually seen it go about midway on the green, once.

I can't say for sure, but it might be on the back of the block.

[TLC87Eagle]

I know on the 258s, they are usually in the back corner of the head, but on the 151, I believe it is on the front of the head close to the thermostat housing.

But why do you need one?

Most AMCs have really efficient radiators that run right at the bottom of green. Especially in this cold, it may not even reach the green unless you block part of the radiator. The only time I've even seen mine up in the green, it was last summer, outside temp was 101 F, and I was holding 70 mph on a hilly interstate running half throttle for extending periods at 2500rpm. It was 3/4 in the green, and I was actually getting worried since I've never seen it that high.

So you may never see it in the green for extended periods.

But one way you can check to see if you have full operation, next time you stop to get gas, and the engine is at operating temp before you shut it off (bottom of the green). After you get in back from getting gas, watch the temperature gauge when you start it. It should go close to middle of the green for a few moments and drop down quickly to the bottom of the green. This is because of heat soak, and it is normal, but a good way to see if your sending unit and gauge are working. You don't have to get gas, but the only way to notice the effects of heat soak is to only stop the engine for no longer than 10 minutes. So even a stop at the quikie mart will give you enough time to give heat soak, if you watch the gauge when you start it.

[Amc1320]

I have never had an AMC temp guage read past where the green starts, have a spirit and it had the 151, it never budged much past the C even on a HOT day, my AMX always goes from the C to the beginning of the green part, never higher, and it had a really HOT heater!

I think its the breed and you are fine,at least thats been my experience

[ammachine390]

Am I the only one who has a gauge that always goes to the exact middle of the green when warmed up?

[TLC87Eagle]

Am I the only one who has a gauge that always goes to the exact middle of the green when warmed up?

What temperature thermostat are you running?
I run a 180 F and mine rests at the bottom of the green, so my guess would be you're running a 195 F.

[carnuck]

When mine goes above the bottom line, I know it's on the verge of overheating! (gotta fix that pinhole!)

[BenM]

I'd try a new thermostat first as well. AMC speced 195 for most cars, and it sounds like you have a 180 if it's not into the green.

[carnuck]

Mine is a 195 (newly installed with the aluminum valve cover). AMC added a resistor wire to the harness that I may remove first to see if it corrects the reading.

[carguy87]

Mine covers about the bottom third of the green.  But I have a 4.0 head, EFI, 195 t-stat, the CJ aluminum Radiator and flex fan.  But in this current weather of about 4 degrees before wind chill, hardly passes bottom of the green.  Before I converted the radiator and fan, it would sit about 1/3 of the way up the green, about the top of the little symbol to the right on the gauge.