[stpackard]

Having no success getting the dash gauge to function with 2 different senders. Old fe390 sender was 1/4” and block is 1/2”not.

Gauge pegs to high when grounding to the block, so it doesn’t appear to be a wiring problem. On a second 1/2” npt senders, first a GM, the second for a 1991 chevy p30 4bt van. Up to operating temp, using a temp gun, block and areas are 145-170 degrees.

sender is at front, have heater core hose at driver side rear to have better heat in winter.

These two senders are short and don’t look long like some pictures I’ve seen, wasn’t sure if they needed fully submerged or if they didn’t extend down long enough like some of the dodge 5.9l senders appear to.

 

[Terry Bridwell]

The element must be submerged in coolant for the gauge to read with any consistency, no matter the type of engine.

 

[Dougal]

Can you get a resistance chart for the sender?

 

[Levis]

Sam, it sounds like you are using a GM sender with the Ford dash and they operate on a very different ohm range. Try using the Ford sender with a 1/4”x 1/2” (Npt) Brass bushing.

 

[Someoldguy]

sounds like you have a grounded sender wire.. a full ground will peg the guage.. you can check the resistance on the sending unit real easy...

 

[Dougal]

How about grounding issues between engine and chassis/body?

 

[stpackard]

Appreciate everyone’s input, thank you.
Engine is grounded to cab and frame so grounding should be covered.

Used a 1/2” brass bushing with 3/8” ford 390 sensor. Sensor is sits higher with the bushing, that’s the reason for trying a few 1/2” non-ford sensors to keep probe tip closer to water.

Dash temp gauge does work, slightly goes above C. 390 ran a bit more above C. I don’t think there’s overcooling going on, using the stock 390 ford non-supercool radiator. At least it’s giving some indication should it go high. Used a temperature gun on the head, block and have 145-170 degrees, don’t know how accurate those are but seems to match what the gauge is saying.

 

[char1355]

If you should have an air bubble in there the Ford sensor would not respond. Might think on another location just to test. Another port would be at the rear side of the head on the driver's side. That port was often used for a cooling fan. That port will also have a hotter reading than the front area. #4 is the hottest cylinder.

 

[Someoldguy]

Appreciate everyone’s input, thank you.
Engine is grounded to cab and frame so grounding should be covered.

Used a 1/2” brass bushing with 3/8” ford 390 sensor. Sensor is sits higher with the bushing, that’s the reason for trying a few 1/2” non-ford sensors to keep probe tip closer to water.

Dash temp gauge does work, slightly goes above C. 390 ran a bit more above C. I don’t think there’s overcooling going on, using the stock 390 ford non-supercool radiator. At least it’s giving some indication should it go high. Used a temperature gun on the head, block and have 145-170 degrees, don’t know how accurate those are but seems to match what the gauge is saying.

you may not have an issue if the gauge moves above the " C" mark... as you are likely running at 145 degrees... those thermo guns are withing about 2 degrees... it may be your scale starts at 130 or 140 degrees so moving up off the " C " mark.. means the guage is working to ... try putting cardboard over the radiator.. run it around the block.. and test again with the electronic therometer... .. I am suspecting you'll need it at 180 degrees to get near the middle of the scale.. as your 390 probably ran close to 200 degrees going down the road

 

[stpackard]

Charley, the driver's rear port I have for heater core supply. Rebuilt the factory ac/heater unit and it never had toasty heat in the winter, so I figured the back port would be best used for the hottest coolant. It's a bit of a rat's nest to get back in there so I might forgo testing the sender at that location at this time.

If you should have an air bubble in there the Ford sensor would not respond. Might think on another location just to test.

Any thoughts on running a temp sender at this location at the passenger front under the water outlet? Being that it is oriented horizontal, that would probably take care of air bubble issues with the bush'd ford sensor.

you may not have an issue if the gauge moves above the " C" mark... as you are likely running at 145 degrees... those thermo guns are withing about 2 degrees... it may be your scale starts at 130 or 140 degrees so moving up off the " C " mark.. means the guage is working to ... try putting cardboard over the radiator.. run it around the block.. and test again with the electronic therometer... .. I am suspecting you'll need it at 180 degrees to get near the middle of the scale.. as your 390 probably ran close to 200 degrees going down the road

Someoldguy, good idea to try cardboard. On a few of these hot days I've heard the dodge fan start running at idle. Should I be concerned about it running too cool? I am running a modest stock ford fe360 radiator.