Looking to match up a temperature gauge that will give accurate reading using the original sending units in a 49` flathead. Would like to use updated gauges. This is going into my AV8.
The problem I had with this was finding out exactly what sender resistance equals what temp on the guage. The sender and guage have to match I had a green line gauge that I could never make work with the replacement senders. No one could tell me what the exact ohm range was of the senders. And you can find this info yourself with a good ohm meter, an accurate thermometer and a pan of water... but you still need to know what the ohm range of the guage is. If the guage dosent match the sender then you need to find a different sender and places like Mac's Bob drake, Dennis carpenter, speedway, and jegs could not give me any useful information about the ohm range for the senders they sell. I ended up getting the guage/sender set below Someone here may have the info you are looking for but I couldn't find it. Chappy 20180317_234047 by Chappy444 posted Mar 17, 2018 at 11:42 PM
The O/P said "original sending units". These do not work by resistance, but are of the King-Seely type that use bi-metallic strips that open and close at rates that vary by temperature. I don't think that there are any aftermarket gauges that will work with them. Probably your only choice are gauges from something else that uses the King-Seely system that you like better. For anything else, you're going to have to change sending units. BTW, "Chappy444", I think those dual gauges are real neat and very appropriate for a flathead cooling system. Can you tell me where you got it? The ones I found on the internet are for snowmobiles and measure exhaust temperatures which are a lot higher.
if not by resistance, how does the signal get from the sender to the gauge? does it actually pass the "heat" to the guage? i am not familiar with that type of sender. as for the gauge..it is made by Westach. they do a lot of aviation and commercial diesel gauges. you will need the guage and 2 senders. the senders are two wire so you do not have to worry about grounding through the threads to the block. the gauge is part number 2DC3-185 Dual (comes in black or white face) the sender is part number 399S7 you will need two and also an adapter (i got mine at Jegs for a couple of bucks each) (full disclosure i had to make a spacer to have them fit in my stock Model A dash with cowl gas tank.) 20180331_124831 by Chappy444 posted Jun 26, 2018 at 8:24 AM 20180407_181015 by Chappy444 posted Jun 26, 2018 at 8:24 AM 20180621_053540 by Chappy444 posted Jun 26, 2018 at 8:24 AM 20180402_054916 by Chappy444 posted Jun 15, 2018 at 9:16 AM 20180401_200153 by Chappy444 posted Jun 15, 2018 at 9:16 AM
Chappy - As I described earlier, the King-Seely system works by using a bi-metallic strip that makes and breaks contact, varying by temperature. This causes the total amount of current put out by the sending unit per period of time to vary by temperature. The gauge has a corresponding bi-metallic strip that reacts to these changes in current. There is a good write-up about the King-Seely system on "The Ford Barn" if you need more information. Thanks for the info on the dual gauge.
The Jalopy Journal
