AMEN..as I recall, stock flatheads used one sender..period.

 

What is the best way to test the temperature sender and switch (one contact and two contact)? I hooked my gauges up after going through them and started the truck. It is the first time that they have worked in years I'm sure as they were disconnected when I got the truck and the wires were not connected properly (but no power to them). I put a new wire running from the right single pole sensor to the taller terminal on the left switch. Then added another new wire from the lower terminal on the left switch to the gauge. The oil pressure and fuel gauges appear to be working just fine. But the temp gauge slowly increases from cold to hot as the engine runs. During the process it starts to increase and then suddenly drops back to cold. Then it goes up again, a little higher this time then drops back to cold again. This cycle keeps repeating itself until the gauge goes all the way to hot and then drops back to cold suddenly. The temp and oil pressure readings have remained constant through this cycle. When I stopped the engine to check for overheating the radiator was just warm and the new 180 deg thermostats had obviously never opened. In addition the electric cooling fan which has its own sensor never came on either. My thought is that that the sensor is not reading correctly? These parts are way more expensive than they need to be ($55 each) so I would like some certainty about what is wrong. Anybody have any ideas? Also are there cheaper substitute parts?

 

Bad sensor, or bad excess temp switch. Disconnect the excess temp switch to tell.

 

Get a six volt power supply, a six volt light, a pot of water and a thermometer. You should be able to tell which is bad based on what the light does when the water heats/boils.

 

That schematic helps. Thanks Ross. I'll try that. I went for a short drive today just to warm things up. I did get the engine up to operating temp and the fan was running but the temp gauge went to hot and stayed there even though the engine wasn't that hot. I went with 180 deg thermostats as Ford recommended in this climate. I can't see that big a difference over 160 deg which is the minimum.

I also found the attached just now at the Ford Barn at http://www.fordbarn.com/forum/showthread.php?t=61832&highlight=temperature+sendi ng

Somewhere today I found someone recommending that you can use NAPA part #MPETS6178 but now I can't find the reference. That is $5.95 vs $55+. Have you heard of this? Can't find the specs on it.

 

The "TS" in that part number is the giveaway, it's a switch. FYI for NAPA there are sometimes manufacturer ID letters, then a functional descriptor, then the number.

NAPA AUTO PARTS

It would work as a replacement Excess Heat Switch, not as the gauge sensor. (Edit -- actually not, since it closes with high temp, not opens)

 

OK my sending units are OK but the gauge starts at H like normal and then moves further to the right off the scale. I would guess that would mean the temp gauge is not calibrated correctly? Is there a way to do this with some degree of accuracy? Anybody know a source for replacement OE gauges?

 

If you ground the wire going out to the engine senders, it should go to C. With that wire disconnected, it should be at H. If the excess heat unit (2-terminal) is bad, it will peg to H. Try bypassing the 2-terminal unit and just connect the 1-terminal unit.

 

Yes, I tried bypassing the 2 terminal unit with no change. Good idea about grounding the gauge. As soon as I do that the gauge falls to C. There is all new wiring going to every unit in the circuit. Both sending units are new. The oil pressure and fuel level seem to be working OK and all have + terminals connected together with stock strapping (see picture attached). Something is amiss . . . What am I missing?

This is functioning just like it did with the old units and wiring before I made any changes.

 

I am certainly no expert, but I believe the single terminal sender is the variable device that measures temp. The 2-terminal is the limit switch that goes open when too hot. I'm changing mine soon to just the 1-terminal sender because I only have one threaded hole in the intake manifold of my not a flathead motor. I'll let you know how it works.

 

You are correct but when I bypass the 2 terminal unit the gauge still stays on hot although the engine is cold and there is power going to the gauge.

 

Are you bench testing the gauge cluster? Because the entire unit needs to be grounded for the 3 gauges to work.

What voltage do you have at the wire to the senders in the engine bay (at the first terminal)?

 

No, testing on the vehicle. Two of the three are working fine. It should be 6v but I'll test it tomorrow at the sending unit(s).

Thanks,

 

Good call Ross. I'm getting 12v at the sending unit. Tracing things back I find that the voltage reducer that I bought from LMC Truck part number 47-3630 (see picture attached) has 12v going into it and 12v going out. They are sending me another one but I'm wondering if this is the right part. eBay shows a lot of options including that one. Napa has a part that you can order but it is $69 C&G Early Ford isn't much better as they have reducers but they go on each gauge. At $20 each plus shipping that is pretty close to the NAPA price. Any recommendations?

 

someone mentioned this home made reducer as described in the tech article attached. i made one up and am using it for my stock gauges. i didn't add the transistor. it cost less than $10 bucks to make one, and a little soldering (in a tight spot).
6 To 12 Volt Conversion Guide .: Articles