New to this Site but need some help: Wiring up stock gauges - still on 6 volt system on a 1949 F-1 with 239 v8, All Gauges work well Except Temp Gauge. Both Thermal Switch and Sending Unit are new, Wiring to Units are new, Truck is Running 160 Degrees After Warming Up, When you Turn Key on and Crank Engine - Gauge goes from Hot to Cold - Good. As Engine Warms up Temp Needle will come to Say 1/4 or Half (Normal) - OK - Then when you idle the truck up - The Temp Needle will Start Back to "C" - Let Engine set at Idle and Needle will Move Back Toward Normal? Any Ideas on Why the Gauge would do this while Idling Up ??

 

Hey Rhildebrand,
Welcome to the forum. Good to see another Texas guy on here with a '48-'50. I've got no answers on your question - electric experts will chime in soon hopefully.

I would warn you that the temp sender on these trucks looks like a wire but it is in fact a hollow line full of a Mercury like substance. We made the mistake of yanking it off to work on an overheating problem. I don't think you want that stuff on your skin.

Good luck over there.

Ben in Austin
1950 F1

 

My guess is that your thermostat is opening and closing causing the temperature readings to fluctuate, and running at fast idle you are moving more air through the radiator causing the engine to cool down. My two cents, it sounds like it is operating ok.

 

But the more you keep it at fast idle - It will go all the way to "C" and stay there until you idle down and it will slowly creep back up ?

 

The new switch and sending unit are for 6V application, right?

 

Yes - Ordered from Carpenter

 

Maybe Bad Switch/Sending Unit - Did a lot of Wiring Today - Looking from back of Gauge - Wire from Ignition on Left Pole - Wire out to Sending Units on Right

 

The oil pressure, temp, and gas gauge all have steel straps distributing power between them, from a wire connected to the Accessory or GA terminal on the ignition switch.

I'd guess you have a thermostat that is stuck open partway, or is real slow to respond. Are the belts reasonably tight? As much as thermostats cost, I'd replace both just so you know they're fresh. I recommend these, they are all the same but branded differently:

Stant 14157
NAPA THM 111
Murray 4157
O'Reilly 2962

https://www.ford-trucks.com/forums/1...l#post14361585

 

Be glad she's running cool. I've done everything I could think of on my 49 f1 239 flathead and she still runs too hot. Looking for s radiator shroud but seems impossible to find one ANYWHERE!

 

Well Maybe I need to Change the Thermostats - I Know the Engine is Running Cool - Still Don't Add Up for the Gauge to Act Normal Until you Give it Gas and it will go all the Way over on the Downside of "C" and stay there until you let it Idle?

 

You have a real head scratcher. The correlation of the gauge and engine speed would seem more of a wiring issue than thermostat performance. I would recheck all the connections. Keep us posted, please.

DW

 

That's what I'm Thinking - Wiring Issue Somewhere - Will be Checking Again Maybe Today

 

What temps are you seeing when cruising at a steady 40 - 45 mph in summer weather? With two independent cooling systems joined at the radiator, and the gauge only on one side, there may not be good mixing of one cold side and one normal side at idle, but enough to change the reading when you rev it up.

 

To rule out a problem with the gauge and sender, I would try temporily swapping over to a mechanical style gauge. That way you can eliminate or isolate it to an electrical issue. Or better yet using an infrared temp gun. Opinions very about where to shoot the temp sample from. I would do it near where the temp sensor is now. Once you rev your engine see if the temperature goes down. You can check both sides and compare. I agree with those who may believe its a thermostat issue. Could be one side is stuck open. Also you mention you installed a sensor and a switch. You didn't accidentally mix them up and put the switch into where the temp sender was supposed to go? Just a dumb suggestion. Its something I would probably do.

 

7RC-10883 .. Instrument Cluster Temperature Gauge / Obsolete

1948/50 F1/F8 & F5/F6 COE

NOS PARTS LTD in Waxahachie TX has ONE = 972-937-2201.

NOS PARTS SOURCE in Olathe KS has ONE = 913-220-5746.