Hi, i hope someone can help me fixing my problem.

I have a ford f100 from 1973 with 302 V8 engine

1. My old temp. Gauge wasn’t working at all.
2. I checked the wiring and the gauge itself (with a small battery)
3. wiring and gauge were ok

4. I replaced the temp. Sensor.
5. Now the temp gauge needle moves a little bit but is always on cold.

6. I guess the ohms range of the sensor and the gauge is not the same.


do anyone has an idea how to fix that?

Is there a way to adjust the ohms range of the gauges? Or so?

thank you!

greetings from Germany

jan-Philip

 

A few ideas...but you might want to state what engine, the year and where it is located. It's probably in the right spot, but sometimes folks move them to after a thermostat or something. The wire will effect the reading if it is bad or has been spliced poorly.

If you are working on the stock instrument cluster, I'd verify with an aftermarket temp sensor first. Your engine might run cold if the thermostat is stuck open or missing. I'm not sure so the rest of the group can jump in...the older Ford cars have voltage regulators behind the instrument cluster which got out of whack over time. Replacing with a solid stat VR usually helped.

I ditched the stock instrument clusters immediately on my 78 F150 and 77 F250...went with Dakota Digital VHX. Love em. Those come with different sensors so I wasn't magically guessing where 1/2 between C and H was.

Good luck!

 

thank you for you detailed response!

i have a f100 from 1973 with 302 V8

and the sensor is at its original place.


the VR was also my guess so I already replaced that. I forgot to mention that.
but it didn’t help.


Yes could be that the thermostat isn’t working properly so I just checked and it is ok.



i think the new sensor I installed has an different range of ohms than my original gauge.

is there a chance to adjust the range of the gauges ohms ?


thank you for your help!

 

I would think it is very highly likely that the new sensor has a different ohm range than your original gauge. Your original gauge might also have some resistance somewhere with the wires and instrument cluster circuit board, although my experience is that they either work or don't other than the VR being out of tune.

Can you adjust the range of the gauge's Ohms? I would guess no, but you could adjust the resistance of the wire going from the sensor to the gauge by adding resistors. You will likely only get a linear change though and you might need a parabolic adjustment. You might also need to decrease the resistance which won't help if you add resistors.

I recommend a few things: (1) Ditch the instrument cluster gauge and get a 3-pack gauge set to screw into your lower dash: Water Temp, Oil Pressure, Voltage. You'll run new wires and use new sending units for precise measurements. (2) See if you can get an OEM temp sender via Ebay. Shouldn't be too hard since I'm sure they were used for a number of years. That might not fix your problem though. (3). You can add (1) and retain your original temp sender so that it at least visually moves a little. You'll need to find another location to put a temp sensor in your SBF. Not sure if the stock intake manifold has another port so you'd have to add it on the thermostat housing which might require you to get a different thermostat housing. Note that you'll read cold until the thermo opens then it will spike. If won't be totally real-time but it will tell you if you are running over 210 and should start getting worried.

I would double-check your thermostat temperate rating - I 'think' that 302 probably came with a 180 degree, but someone may have put on a 160. The 302 for trucks 'might' have come with a 190/192/195 thermostat like my 400M did. The gauge might be set for a temp range higher than the current thermostat so it will never read right from C to H. I have several SBFs and I run 180 on cars and 190/192/195 on my trucks but I run precise gauges so I know how hot or cool they are.

Good luck!

 

what does the gauge do when you ground the sender wire? Using your ohm meter, what is the resistance from ground to the connector on the sending unit when cold (I think it should be around 75Ω)...and what is the ohm reading when fully warmed up (it should drop as it warms up)? You can run the same test by heating it up in a pot of boiling water. Did you use any type of teflon tape or thread sealant when you installed it?

as mentioned above, you can increase the resistance by adding resistance in series. You can decrease the resistance by adding resistance in parallel with the sender, but it even if you could get the correct range, it would be better to get the correct sending unit.

 

oh wow! Thank you so much for that helpful reply !!

i will check what you mentioned!

big thank you!

 

thank you!

if I ground the sender wire the gauge goes all the way up to hot. Further than the scale.


I’ll check the ohms with an ohm meter when I’m back home! Thank you! Also really helpful!

 

I agree with dlburch on the teflon tape.Maybe it is not getting good ground.Is all your other gauges working or are you having issues with them fluctuating?Could it maybe instrument cluster regulator?(just guessing here).Are you sure you have correct part #?
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