Cold weather gauge gremlins (1 Viewer)

[Chestcutter]

With the single digit temps we have been having, I've noticed a new electrical phenomenon. After sitting all day at less than 20 degrees, the truck starts on the first turn with full choke, the temp and ammeter work, but the oil pressure and gas gauge sit at zero.

When the engine warms, temp gauge shows appropriately, but oil and gas stay at zero. When I turn the heater on and the cab warms, first the oil pressure gauge works, then the gas gauge a few minutes later. Lately if it is really cold the left turn signal doesn't work, but starts to work before the oil pressure as it warms up.

Any ideas?

 

[Engineer8000]

The temperature gauge and fuel level gauge work off the same voltage regulator in the fuel level gauge. It is a point type regulator that has a heated bi-metal strip to make it work. I'm guessing the bi-metal heating doesn't work great when it's cold. I don't have anything to add on the turn signal.

 

[sggoat]

The oil psi sensor may have a little sludge or restriction in the sensing hole, blocking the sensor from seeing the actual oil pressure til it gets warm(esp if you have an oil cooler)--search the forum for gauge cluster indications or the oil psi sensor--there is a definitive post about the internal workings of the sensors(I can't remember the poster exactly--BJ40 Green? Coolerman?
The fuel gauge might also be subject to the cold(it is a resistance device, and subject to temp fluctuations-might be a ground issue)
The turn signal is a mystery--what about the right signal-does it do the same thing?--the flasher is a resistance device as well--Are the ambient temps abnormally low in your area?
What year LC?
I'll look for the post(s)

 

[sggoat]

Found it--The poster is BJ40 Green(Rudy)--search his threads for clusters/gauges--loaded with good info
The fuel level gauge is tied in with the temp gauge-and the oil psi switch-gets the 12v from the heater fuse. I cannot find any fj40 that has a heated bi-metal strip in a fuel regulator(not sure what that is)-the fuel gauge is a simple "potentiometer"(a resistance winding with a wiper that varies the resitance with the level arm)-but that may depend on the yr of your 40-ie. post 1980--also depends on what the PO did behind the cluster-----

 

[Engineer8000]

fuel gauge, 7v regulator on the right side.

 

[Chestcutter]

Thanks guys. The voltage reg makes the most sense given this only seems to depend on the cabin heat. If I leave the heat off they stay at zero even with a very warm engine.

Turn signal remains a mystery. Given the weather is starting to warm I may not chase it too hard - on the future projects list when I need to remove the cluster for something else.

 

[B y r o n]

If the right turn signal is working but the left isn't I'd start by checking all your connections and grounds.

 

[sggoat]

Thanks to eng-8000-that pic is great! I never really spent much time in the cluster gauges--all the wiring diagrams I have do not show that detail..
It appears the 'contact' arm(bi-metal strip(?) , is wrapped in resistance windings fed from the 12v supply. -is that true?
Seems like the windings are what heat the strip to allow the points to close, applying the nominal 7v to the temp/fuel gauge.
(Wiring diagrams do show a resistor in the temp circuit).
If the temp and fuel level work off the same 'regulator' wouldn't the temp gauge be inop as well?

this is good t'shooting info

 

[Engineer8000]

After I posted that I realized it didn't make sense. There is resistance wire wrapped around a bi-metal strip. As more current flows the strip heats up and bends to open the contact. What I have seen is that regulator stops working and causes the fuel level and temperature to read high. Doesn't really fit your situation. I'm old and it was late, poor excuse.

 

[sggoat]

After I posted that I realized it didn't make sense. There is resistance wire wrapped around a bi-metal strip. As more current flows the strip heats up and bends to open the contact. What I have seen is that regulator stops working and causes the fuel level and temperature to read high. Doesn't really fit your situation. I'm old and it was late, poor excuse.

I can offer the exact same excuse---what you did do is help me learn a bunch of stuff about the cluster that I never knew--thank you for that--