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Odds are that even if you use the stock sender it's going to read more towards the H than the N on the gauge since newer engines run hotter than older ones. Since the gauge just has C N and H, I would think if you know the gauge ohm readings for cold and hot, you could split the difference and come up with a sender that would put the needle in the Normal range when the engine is at operating temperature.
....and purely a guess here - but for all the newer stuff, the sender is designed to send a signal to the ECU/body computer -- and it manipulates it and sends a signal to the gauge. I know on the tachs -- it's a 5V signal. So that has to be dealt with if you're using an older tach that's expecting a 12V signal. I'd guess the same is true of the other gauges -- they're set up for 5V signals. So I'm wondering if you could use the contemporary senders with 1940 Mercury gauges at all.
However, to Nova71's point -- my car's original gauge/sender was expecting a lower operating temp than the LS3 runs at. So I had to install a small resistor in the gauge signal line to move the coolant gauge needle from the upper end of the range, to something closer to the middle under normal operating conditions. So now, when I'm under cruise and the head temps (from ECU data read) are around 195F - the gauge shows a bit below halfway. And when the fans are controlling temp (head temps around 199F-202F) the gauge reads just a bit above halfway.
Im not quite sure. From what Ive read and been told, the best way is to incorporate the original senders that the gauges came with. Everything is going to work like stock, EXCEPT the temp gauge... I took the cluster the my local speedo shop this morning and the guy said he could manipulate the stock guage to communicate with a newer sending unit. 80's Ford truck or something like that.
If you want to retain the original gauges there are companies that will convert them for you. The amps gauge will be converted to volts, gas gauge will read correct and the speedo will be converted to electronic. This isn't cheap but you will not need a bunch of gauges dangling under the dash. If you decide not to go this route do not hook up the amp gauge due to fire hazard. The old electrical system would generate 30 amps tops and the new 12 volt system with fans and a/c will be double that. The gauge just can't handle it.
It actually is a volt meter. Should be fine with the 6v reducer, right?
so, I went to my local speedo shop and got the stock temp sweeping gauge replaced with a 68-94 ford unit (very common) and looks exactly the same in the face.
I then bought the appropriate 1/2" sending unit and chucked it up in the lathe, shaved it down and threaded it with a 12-1.5 metric Die. Works beautifully, put it in the pass side head where the plug was. I now have the stock sender for the ECU to read, and the stock gauge to read temp.
Nice work! Just keep in mind, the way water moves through the engine, the ECU sensor picks up coolant temp as it's leaving the engine on it's way to the rad. So the coolant has picked up all the heat it's going to at that point and is likely registering the warmest temps. The same location on the passenger side head (at the rear of the motor?) will likely be a few degrees cooler.
Nice work! Just keep in mind, the way water moves through the engine, the ECU sensor picks up coolant temp as it's leaving the engine on it's way to the rad. So the coolant has picked up all the heat it's going to at that point and is likely registering the warmest temps. The same location on the passenger side head (at the rear of the motor?) will likely be a few degrees cooler.
i understand and thank you. The ecu temp sender is in the normal spot. I hooked the gauge sender C/H to get a (ballpark reading) of where I'm at. I'll check actual temperatures and see where My gauges are.
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