All I can say is there seems to be some sound reasons for either
choice. What I like about using the temp as the water exits the
radiator is that the fan only comes on when it is needed, i.e. when the
coolant isn't being cooled by the radiator. For example, if you were
pulling fast up a steep hill, the coolant leaving the head might be
getting hot, but upon exiting the radiator, it might be fine. Running
the fan wouldn't help in this case.
The current setup I have now seems to keep the temperature (measured at
the thermostat housing) much more constant than when I had the switch
at the top of the radiator. Could be that it was just a function of
the switches, and that either place could behave the same.
In some sense I think measuring after the radiator gives you an earlier
warning, as the too-hot coolant leaving the radiator has to make it all
the way back through the engine before it results as too-hot coolant
leaving the engine. (I realize that in practical terms that probably
doesn't make a difference).
I guess the best answer is to have a switch in both places!
On Sunday, April 6, 2003, at 07:22 AM, Gerald Van Vlack wrote:
> Darrell, My car has the "approximate" type gauge. It is the original
> gauge that came with the car when I bought the car in 1969. It shows
> the hot zone only as a red mark. I've been in the red zone while in
> traffic and it's not something I've enjoyed. The car is Commission #
> 69150L. I can't comment on what's correct for your car although the
> Factory Spares Manual I have shows your style gauge and lists convex
> glass as the replacement glass, I am reasonable sure that the convex
> glass went away with the early 4's. So it goes for the arguments about
> originality and the records to support "facts"!
>
> I've done some profiling of the temperature vs. the needle location to
> determine the spot that is 180 to 190 and on mine it's just above the
> center of travel. The sending unit has a lot to do with the location
> of the needle too. I have two sending units and by switching them I
> can move the needle about 1/8 inch on the gauge. I profiled the gauge
> by using an accurate thermometer and measuring the water temperature
> at various positions on the gauge, making a mental note of the
> operating range where the car seems to run the best.
>
> While it would be interesting to know what the water temperature is at
> the outlet of the radiator, my preference is to know what the water
> temperature is at the hottest point in the engine, after all that is
> what the manufactures measure and the reason for me placing the probe
> at the top of the radiator. Another way to look at it would be this.
> What if the fan belt broke or for some reason the water pump was not
> circulating water. The engine would quickly begin to overheat but the
> temperature at the bottom of the radiator may not change for quite
> awhile since that water would be cooled but not being circulated into
> the engine. The fan probe located at the bottom of the radiator would
> show things to be OK while they clearly are not and the radiator fan
> would not be coming on. The temperature gauge would show a problem
> since it's measuring the temperature at the engine water outlet. While
> I do look at the temperature gauge on a frequent basis, the red light
> that is wired into the circuit showing that the fan has come on makes
> me look at the gauge and continue to monitor the gauge until the light
> goes off.
>
> These are my arguments for measuring at the top of the radiator.
>
> "That's my story and I'm sticking too it". :-)
> JVV
>
--
Darrell Walker
66 TR4A IRS CTC67956L
Vancouver, WA, USA
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