Function testing factory Gauges.

[HotRodPC]

You have a DVOM? Just do a voltage drop test.

Set your volt meter to DC volts, Touch negative lead to Battery negative POST, then touch your Positive lead to the case of the sending unit. Observe voltage reading. Anything more the .03 - .05 volts is excessive.
Another way to test for voltage drop is to:
1. measure the battery voltage at the battery POSTS. Record your readings
2. Connect negative lead of the multimeter to the case of the sending unit.
3. Connect positive lead to Battery Positive POST. Record your readings.
You shouldnt see anymore then a .03 volt difference from testing direct to the battery versus the sending unit case.

IF you see more then a .03 difference then touch the negative lead to the engine block, should be within .02 volts of battery voltage.


Your questions brings up a question for me though. There seems to be alot of electrical questions and problems from time to time. I have been thinking about doing a techincal write up on Proper procedures for testing electrical systems.
Would this be something that anyone would get any use out of or would I be wasting my time?

I'm certain a select few would get use of the proper technique to electrical test. I always look at book in most cases, like to test sensors, coils (both sides) and modules and such. I don't even bother trying to memorize since I know I'm going to going to have the look up the specs anyway.

On this Temp guage and the voltage test... So a Volt reading is the way to do it huh? So I got this all wrong then. I figured the gauge was 12v hot as soon as the key comes on, then then the sender grounds through a thermistor however spelled, or thermal resistor, and the ohms measured through the thermistor is what made the guage read, and why with a grounded out gauge wire is why the guage pegs infinite. In short that's what a guage is in most cases. It's actually a ohms meter with a different scale.

I think what I'm testing here for is a defective NEW or WRONG Sending Unit. Being the gauge Parks where my other Temp Guages Park without power, and that it pegged infinite when the wire was grounded, is telling my, my wire is good and that I have the right wire on the sender, also another tell tale that the gauge should function. So I"m expecting either, the Teflon Tape is not allowing a ground to the head, #1, The sending unit is wrong part #2 or that the sending unit is DOA out of the box #3.
So I'll give that a try, maybe that's why I've not figured this out yet. I also haven't looked at any books yet either.

 

[oneluckypops]

I'm certain a select few would get use of the proper technique to electrical test. I always look at book in most cases, like to test sensors, coils (both sides) and modules and such. I don't even bother trying to memorize since I know I'm going to going to have the look up the specs anyway.

On this Temp guage and the voltage test... So a Volt reading is the way to do it huh? So I got this all wrong then. I figured the gauge was 12v hot as soon as the key comes on, then then the sender grounds through a thermistor however spelled, or thermal resistor, and the ohms measured through the thermistor is what made the guage read, and why with a grounded out gauge wire is why the guage pegs infinite. In short that's what a guage is in most cases. It's actually a ohms meter with a different scale.

I think what I'm testing here for is a defective NEW or WRONG Sending Unit. Being the gauge Parks where my other Temp Guages Park without power, and that it pegged infinite when the wire was grounded, is telling my, my wire is good and that I have the right wire on the sender, also another tell tale that the gauge should function. So I"m expecting either, the Teflon Tape is not allowing a ground to the head, #1, The sending unit is wrong part #2 or that the sending unit is DOA out of the box #3.
So I'll give that a try, maybe that's why I've not figured this out yet. I also haven't looked at any books yet either.

The gauge itself has 3 wires
1. 12 volt ignition hot
2. Ground
3. Signal wire from sending unit.

An easy way to think about how the gauge works is to think of it as a RELAY. The gauge is constantly grounded via the ground wire, when the ignition is in the run position 12 volts are applied to the gauge. When the gauge has 12 volts it energizes the coil which switches the ground path to the sensor wire.

The Sensor is a thermo resistor. When the Temperature is cold the resistance is HIGH. When the temperature is Hot the resitance is LOW.

Resistance is measured in ohm's, NOT volts. When I said to set your DVOM to DC volts it was strictly to measure "voltage drop" of the circuit. To test the temperature sensor you would set your DVOM to ohms. Measure the resistance at room temperature between the probe that sticks inside the head and the terminal. Then heat the sensor up and re test.

0*------- 25,000 ohms
20* ------13,500 ohms
40*-------7,500 ohms
70*-------3,400 ohms
100*------1,600 ohms
160*------450 ohms
210*------185 ohms

Voltage drop tesiting is used to find inadequate connections, (loose or corroded connections)

 

[HotRodPC]

Ahhh OK, there's the difference I was looking for. A IDIOT light, only has 12 Volts to the Light and NO ground. When the SWITCH, NOT SENDER, reaches it point going closed, then it grounds and turns the light on. I was ASSYOUnMEing that the Gauge worked the same way, with the Thermistor or Thermal Resistor gradually took care of the grounding and fed the info to the gauge. So the gauge has constant hot and ground as soon as the key is on. Then the 3rd wire is for the gauge to read the resistance from the SENDER.

I've decided I'm going go ahead and trust the OE Electric guages, BUT, I'm also adding Idiot Lights, like I did on my 64 GMC. The gf's and my dad would drive the truck occasionally and my motor wasn't all that cheap. So I had nice Stewart Warner Mechanical guages, but not trusting them to pay attention to them or even know what the hell they meant, I had lights, and they were told if ANY RED light comes on at all, then you shut it off, and I don't care if you sitting in stop and go traffic on I-5. You shut the fugger off and push it to the side.
Had Oil Pressure Switch, obviously no pressure, RED light by the Oil Pressure Gauge came on. On the Temp, cuz the truck ran hot with a biggo cam in it and sitting in traffic it would get up to 220 and sometimes 230 and that was normal. The truck was also a manual choke carb. So I had 3 temp lights. Blue For Cold, Yellow for Caution, pay attention to the guage that came on at 210, and Red for Hot that came on at 253 degrees. Sitting in traffic, it was always yellow. They were told, full choke to start, then go half choke. When the blue light went off, then shut the choke off. Truely was IDIOT proof.
Don't think I need the Yellow Caution this time, but I'm doing the Blue light that will shut off at 100 degrees, then I know I can get some warm air out of the heater. Also helps let you know if your fail safe thermostat is stuck open. When it normally takes about 4-5 minutes for the light to go off, and now it's taking 15-20 minutes in the cool months, you know your Tstat is stuck open. Not running Fail Safe Tstat anymore either. I'm sick of them sticking open.

 

[HotRodPC]

I vice grip clamped a bare 10gu wire to the sender Hex, alligator clipped the other end to the negative battery post, so I know the bitch was grounded. Ran the truck till the heater was blowing warm air and the gauge never moved. Doing research on BWD Engine Management Products, they're made in China. Go figure. I think I'm about to consider this a defective sending unit since all the other signs that the guage works are there. It parks without power where it supposed to. It goes to Zero aka 100 when it gets power, and it goes full infinite when the guage wire is grounded. That's 3 things that tell me the gauge SHOULD be good. Figured out, AutoZone Duralast Senders are most likely AirTex Wells, made in USA, and same part # Rock Auto uses specifically for my truck, but AZ calls it their Duralast Brand, so I'm going to AZ to get the Sender for $7, which is $4 cheaper than the BWD sender at Advanced Auto. I'll give this a try and if it don't work, then I start pulling the phukin dash apart.

 

[HotRodPC]

Waiting for the truck to cool then swapping to this Airtex Wells/Duralast Sending Unit. The heater worked great of course. Just like roasting my nuts on an open fire !!! I did get something out of the guage though on this longer drive than just letting it warm up a bit in the driveway. When the heater started blowing real hot, I noticed the gauge got up to say 110 or thereabouts off of 100. About just as soon as it got there it dropped back to 100. Got back up to the 110 or so again, then dropped back to 100. That's telling me, with this new thermostat, that 180 is reading 110, then the stat popped and dropped the temp back down. So this too also leads me to believe I have either the wrong gauge sender or defective sender and that my gauge will work fine after the swap.

What sucks, is how the hell amd I going to catch this brand new fuggin Coolant I just put in to swap the senders? I don't have a pump to draw enough out. I do actually but what I have would take 3 days plus a lunch break to get enough out of it. At $13 a fuggin gallon, I'm not wasting brand new Coolant. I got a 5 gallon bucket to drop the lower hose but that only catches about 25% of it since the frame rail is in the way.

 

[oneluckypops]

Waiting for the truck to cool then swapping to this Airtex Wells/Duralast Sending Unit. The heater worked great of course. Just like roasting my nuts on an open fire !!! I did get something out of the guage though on this longer drive than just letting it warm up a bit in the driveway. When the heater started blowing real hot, I noticed the gauge got up to say 110 or thereabouts off of 100. About just as soon as it got there it dropped back to 100. Got back up to the 110 or so again, then dropped back to 100. That's telling me, with this new thermostat, that 180 is reading 110, then the stat popped and dropped the temp back down. So this too also leads me to believe I have either the wrong gauge sender or defective sender and that my gauge will work fine after the swap.

What sucks, is how the hell amd I going to catch this brand new fuggin Coolant I just put in to swap the senders? I don't have a pump to draw enough out. I do actually but what I have would take 3 days plus a lunch break to get enough out of it. At $13 a fuggin gallon, I'm not wasting brand new Coolant. I got a 5 gallon bucket to drop the lower hose but that only catches about 25% of it since the frame rail is in the way.

Something I like to always try to do to my vehicles when I have the coolant system empty, is to remove the drain plugs in the block. Then install a spring loaded ballvalve in place of the plugs. That way if I need to change a coolant part I can simply atach a hose to the valve and run it into a jug, open valve and drain the block. Seems like alot of extra **** but I HATE WORKING IN OR AROUND SPILLED ANTIFREEZE!!!!!!

Did you do a voltage drop test? What was your reading?
Will you please test the temp sensor for ohms at the temperatures I have listed above, I am sure you are correct and the sensor is faulty but am also curiouse to see what the readings are.

If by chance it doesnt fix it dont go tearing the dash apart just yet. There are still other possabilities that it could be. NOT LIKELY but still possable.

 

[89Suburban]

Something I like to always try to do to my vehicles when I have the coolant system empty, is to remove the drain plugs in the block. Then install a spring loaded ballvalve in place of the plugs. That way if I need to change a coolant part I can simply atach a hose to the valve and run it into a jug, open valve and drain the block. Seems like alot of extra **** but I HATE WORKING IN OR AROUND SPILLED ANTIFREEZE!!!!!!

That is a good, affordable mod there. Even if the lower hose is dropped, the coolant in the motor only lowers down to the ports on the water pump.

I know it's a pain in the ass HR but you could bungee a old t-shirt or cloth over the drain pan/bucket to filter.

 

[HotRodPC]

12.66 at Battery, WO Motor Running
12.66 Grounded to Sender Casing with Vise Grip Clamped 10gu wire so it would reach to the negative lead on the DVOM.

Difference Zero

12.65 Grounded to the Passenger Side Head.
Difference .01.

 

[HotRodPC]

That is a good, affordable mod there. Even if the lower hose is dropped, the coolant in the motor only lowers down to the ports on the water pump.

I know it's a pain in the ass HR but you could bungee a old t-shirt or cloth over the drain pan/bucket to filter.

I"m not worried about filter. I know it's clean. I need to find a way to catch it in a 5 gallon bucket so I can pour it back in. I also don't like fluids in the driveway of any kind and I damn sure don't want to spend more cash on AntiFreeze even if it is on sale for $10 from $14 a gallon. I'd use the drain **** on the radiator but it doesn't have a spout for adding a hose like many I've seen do.

 

[HotRodPC]

I lost about 1/2 gallon of coolant, so at a 50/50 mix lost about a quart of Anti-Freeze.

And, guess now it's safe to assume IT IS the gauge that is bad. Still not working, and won't even go up to 110 now when the Tstat pops. Still works the same. So the + and - on the gauge are working properly, but the reading of the thermistor isn't happening. I find that weird being I can ground the wire and it goes infinite. Fugg it. I'll get the dash apart. The heater is working awesome though.

 

[89Suburban]

I lost about 1/2 gallon of coolant, so at a 50/50 mix lost about a quart of Anti-Freeze.

And, guess now it's safe to assume IT IS the gauge that is bad. Still not working, and won't even go up to 110 now when the Tstat pops. Still works the same. So the + and - on the gauge are working properly, but the reading of the thermistor isn't happening. I find that weird being I can ground the wire and it goes infinite. Fugg it. I'll get the dash apart. The heater is working awesome though.

 

[oneluckypops]

I lost about 1/2 gallon of coolant, so at a 50/50 mix lost about a quart of Anti-Freeze.

And, guess now it's safe to assume IT IS the gauge that is bad. Still not working, and won't even go up to 110 now when the Tstat pops. Still works the same. So the + and - on the gauge are working properly, but the reading of the thermistor isn't happening. I find that weird being I can ground the wire and it goes infinite. Fugg it. I'll get the dash apart. The heater is working awesome though.

Hold on there grass hopper... Doesnt mean it is the gauge. The problem could still be in the sensor lead to the gauge. Remember HIGH restitance means LOW temperature. You do need to get access to the IP plug. then do a voltage drop test at both ends of the wire. It could very well be the wire is cut and or frayed causing the exsessive resistance.

 

[HotRodPC]

I didn't pull it apart yet. I have followed the wire to the fuse block at the firewall and the wire is fine to that point. So whatever it is or where the problem is, it's going to be between the interior firewall to the cluster and/or gauge. I knew I hated ****** Electrical Gauges for a reason, ESPECILLY OE Gauges. And I think I'm getting the resisantce backwards. IIRC, the Switch is Opposite a Sender right as far as HOT resistance. One is Low Resistance at HOT, and one is High Resistance at HOT. Gotta run again !!!

 

[oneluckypops]

I didn't pull it apart yet. I have followed the wire to the fuse block at the firewall and the wire is fine to that point. So whatever it is or where the problem is, it's going to be between the interior firewall to the cluster and/or gauge. I knew I hated ****** Electrical Gauges for a reason, ESPECILLY OE Gauges. And I think I'm getting the resisantce backwards. IIRC, the Switch is Opposite a Sender right as far as HOT resistance. One is Low Resistance at HOT, and one is High Resistance at HOT. Gotta run again !!!

To accuratly test the gauge you would need a potentiometer that can read from 1600 ohms (100*) down to around 90 ohms (250*). But you can still test the sensor circuit with voltage drop tests all the way to the gauge.

Fuel gauge sending unit is 0-90 ohms
0 ohms and the gauge should read Empty
22.5 ohms and the gauge should read 1/4 tank
45 ohms and the gauge should read 1/2 tank
67.5 ohms and the gauge thould read 3/4 tank
90 ohms and the gauge should read Full

Temperature gauge is

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[HotRodPC]

Fugger !!! I just downloaded that and was coming to edit your post and put it up.

That's good info there.