[DeTomaso] Fw: temp sending unit

[MikeLDrew at aol.com]

In a message dated 2/23/08 6 41 37, gaino at earthlink.net writes:


> >I just replaced my heads with new valves and added some new hoses etc. My 
> temp gauge never really worked like it should. I pulled the wire from the 
> sending unit on the swirl tank and grounded it, it pegged the gauge. Now what 
> sending unit do I need to put in my tank. It appears to be 3/8 npt.  I better 
> make sure the tank is grounded, now that I write this I'm thinking of all the 
> FORD blue I painted on that tank. I still want to know what sending unit... 
> Thanks Bill
> 

First of all, you do *not* want to have a temp sender in the water tank!   I 
know that's where De Tomaso originally put it, but they were really dumb to do 
so.

There is an identical port on the front of the engine, facing straight 
forwards, just above and to the left of the water pump, and next to where the 
thermostat lives.   Panteras came with a plug in that hole.

Hike down to your neighborhood auto parts store and ask for a temp sender for 
a '72 Mustang with a temperature GAUGE.   They make senders for both a gauge, 
and an idiot light, and they look identical.   The one for the idiot light is 
an on-off switch, so your gauge would either read zero or fully pegged.   You 
need the one for the gauge.

Pop the cover off to get access to the front of the motor, and perhaps drain 
a little of the coolant to get the water level below the plug if you already 
filled it.   Be armed with towels to catch anything that flies out, and protect 
your interior.   Remove the plug, insert the temp sender.

The wire which was going to the tank will thankfully reach to the new 
location without modification.

With the cooling system topped off, and the pressure cap removed, with a 
towel wrapped around the water bottle and secured somehow (duct tape), get an 
ordinary meat thermometer, punch it through a small piece of cardboard (larger 
than the water bottle opening), and then insert the probe into the water.

Now, start the car, and stand at the right rear of the car, where you can see 
the thermometer, and also look through the back window and see the water temp 
gauge.   As the engine warms up, you will see the temp gauge rising, while 
the water in the tank remains cold (because the thermostat is closed).   At 
about 180 degrees, you should be able to 'see' the thermostat open, as the temp 
gauge on the dash will drop slightly, water will start to flow through the 
system, and the temp gauge on the thermometer will rise.

Eventually, the two should read equally; there may be some splashing of water 
on the ground while this is going on.

This is simply to verify the accuracy of the temp sender.   If there is a 
great different between the actual water temp, and the temp on the gauge, then 
you can introduce a resistor in the line to lower the reading on the gauge, if 
necessary.   Mine happens to be spot-on, thankfully. :>)

If you haven't already filled your cooling system, realize that there is a 
rather complex and iterative procedure for doing so properly.   You can't just 
slam some water in until it appears to be full and call it good.   You will 
have to elevate the rear end, fill the system with the radiator bleeder open 
until water streams from the radiator, then close the bleeder, and fill the 
overflow tank half full.   Start the car, let it warm up, and when the thermstat 
opens the water level in the tank will drop suddenly, in fact it will probably 
empty immediately.   So you will have to keep topping it up.   When the tank is 
full again and water is flowing, start cracking the bleeder on the radiator 
again, venting as much air as you can.   You will think that you have the system 
fully bled, but when you shut it down and let it cool for a few hours or 
overnight, you will find that you have to add a bunch of water again.   Do this 
2-3 times, then fill the overflow tank about half full.

I actually chose to over-fill my overflow tank intentionally, to allow the 
cooling system to reach its own statis point.   The stock overflow hose is route
d to the ground right in front of the rear tire--dumb.   Plumb a longer hose 
and route it towards the rear of the car so that any overflowing coolant will 
be jettisoned aft of your car and become somebody else's problem. :>)

With my car so-filled, I found that for the first half-dozen times or so that 
I drove it, whenever I would park, a little bit of excess coolant would 
dribble out of the hose when I shut down.   it was slightly embarrassing, but then 
again, I knew it was intentional so I didn't let it bother me overmuch.   
Evenually the water level reached its happy point and it's been perfect ever 
since.

With a 180 degree thermostat fitted, my car will idle for weeks at about 190 
degrees with both fans running, and typically run about 180-200 when on the 
fly.   I did note on one high-speed run through the desert that my water 
temperature started to creep upwards towards 230.   I plan to address the situation 
with some improved ducting (preventing the air from being allowed to flow 
around the radiator, especially from below).

Mike


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