Re: [AMC-List] Water temp unit

["John Elle" <johnelle@xxxxxxxxx>]

SNIP
Jay wrote:
> Now I know why AMC moved the temp sending unit from thr front of the
head
> back to the rear of the head.  The darn fan cools the unit off so much
up
> front, you never get an accurate reading.  This is on the 232 /258
engines
SNIP
 
I am not sure that is really a valid reason, the sensor is buried deep
into the head and in the water jacket. I don't think any of the air
coming from the fan would have much of an affect on the reading of the
sensor due to the mass of the head and the water.  If I had a question
to ask, how valid is reading off of the top back corner of the cylinder
head. Water flow has got to be less than wonderful in that location.
Bottom line for me is, my 1980 AMX gauge and readings are just as good
as the readings in my 1980 Spirit with a 1975 engine. I don't really
think that they are all that accurate anyway.
 
SNIP
Does anyone know if there are different value senders? 
SNIP
 
Here are readings used to test gauges from 3 different TSMs. 1970, 1974
and 1980 plus the gauge packages. 
 
Given the test equipment available in 1970 my guess is that the 1970 and
1974 use the same sensor. The 1980 uses a different sensor and the gauge
package different again as the voltages are different using the gauge
package.
 
 
1970 TSM values:
73 ohms cold  125F
35 Ohms operating band cold side 165F
13 Ohms operating band High side.  235F
9 Ohms Hot. 267F
Specifications for Hornet
 
1974 TSM 
73 Ohms Cold 130F
35 Ohms 171F degree, beginning of band.
13 Ohms 242F degree, top of band. 
9 Ohms 270F degree, hot.
Specifications for a Hornet
 
1980 TSM Values 
353 Ohm Cold, 147 Degree F 
192 Ohm Bottom of Band, 180 degree F
73.9 Ohm top of band, 242 degree F 
45.2 Ohm Hot, 280 degree F
Specifications for a Spirit, AMX, Concord and Eagle. 
 
Accuracy is supposed to be +/- meter needle width.
 
Gauge Package temperature gauge sending unit.
114 Ohm 190 degree F. 
48.8 ohm 280 degree F. 
 
Keep in mind that as you go through the '70's smog control was aided by
running the engine hotter so there has to be some playing around with
that reasoning. 
 
My Spirit uses a 1975 engine with the heat sensor located up front, the
gauge sensor screwed into the back of the head fits the hole in the
front of the engine just fine. The Fuel Injection wants a 195F
thermostat which is installed in a replacement thermostat housing that
was also designed to hold the heat sensor for the fuel injection engine
controls. Due to an interference with the A/C brackets that was not
possible to do so a plan B was used. Plan B was suggested by the fuel
injection installation instructions. A fitting was procured that fit
into the heater hose going to the heater control valve which is
controlled by the A/C controls. Water flows constantly through this line
and is directed back into the engine when the heater is not used. Eg.
Off and A/C are being used. A non-A/C Spirit will not have this valve
but water will flow continuously through the heater as cabin heat is
adjusted by mixing fresh air with the heated air from the heater core
rather than adjusting the hot water flow. 
 
Engine heat was stabilized by having a 3 core radiator built, installing
a fan shroud (there was not one on this car) and using a functioning
clutch fan. The temperature gauge sits constant at mid scale with very
little fluctuation. Today it was 112F, the car runs cool. With out the
radiator fan shroud the engine would run hot when sitting at stop lights
with the A/C going on triple digit days. 
 
The car needed a new radiator. Surprise! A 20 year old beater really
does not have much of a good radiator left in it. A new 2 core radiator
went into the AMX also due to advanced plugging of the factory radiator.
But lacking A/C a new aftermarket A/C radiator (bigger) went in with a
fan shroud. This car did not have a fan shroud either but it did have a
little weenie non-A/C radiator.
Fan Shrouds were easily available from junkyard Eagles. An I-6 and V8
Fan Shroud is different as the I-6 fan is just a bit off center, but if
you are careful on the mounting of them they will work with the OEM fans
when swapped back and forth.
John
 
 
 
 
 
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