Prescribed temp per ohm reading, f or example: @ 100f on your infrared gauge, with your ohm meter connected to the Pos. Terminal of the sender and Neg. Terminal to the exposed brass case of the sender you should see an ohm reading of 450 ohms. Correspondingly, the same procedure can be followed at 175f where the ohm reading should be 99 ohms. Temperature Gauge - pointer to temperature of engine water. 2) With the key. As you add gas, the ohm reading will go up until tank is full and reads 180 ohms.
I'd like to bench test my temp sensor while i have my engine apart. I wasn't getting any readings on the temp gauge when it last ran (overheating wasn't the reason for the overhaul).In videos i've seen online on testing temp sensors in boiling water, they use pigtail attachments to the end of the sensor, with a hot and a ground wire to then attach to a multimeter.However the sensor i have has only the single post for what i assume is the hot.Which makes me wonder -How can I do this?And also, when in the engine, how does the temp sensor work without a grounding wire to complete the circuit? Could it be that is in fact why i wasn't getting a reading before? The thing was just wired incorrectly by the PO? To elaborate a little on Simon's (HalcyonS) point, the sender is a variable resistor and is measured with an ohm meter or a multimeter set on the ohms scale.
There is no hot or + lead involved.The way the gauge works (same with oil pressure) is 12V + is connected to the 'I' terminal on the gauge and a single lead is connected from the gauge 'S' terminal to the post on the sender. The sender varies the ground path and therefore the circuit voltage for the gauge.So for the dumb Polacks in the crowd (me) what ohm reading should you be looking for when you put the '+' probe of the multimeter on the 'post' of the sensor and the '-' probe on the threads to indicate the sensor is good? So for the dumb Pollacks in the crowd (me) what ohm reading should you be looking for when you put the '+' probe of the multimeter on the 'post' of the sensor and the '-' probe on the threads to indicate the sensor is good?Not so dumb, actually a great question.Which I cannot answer!It depends on the sender. Different types/brands of sensors have different resistance ranges and react differently to the same temperatures. That's why gauges and senders must be properly matched. If you can find the specifications for your particular sender the resistance range should be included.The best test I can think of would be to attach the sender to your gauge including a 12V source for the gauge and compare the gauge reading to a thermometer in the stovetop pot where the sender is immersed. I'd be careful to insulate the wire connection at the sender so any continuity through the water doesn't skew the readings.
I forgot to hit the 'subscribe' button to this thread and had no idea there were so many answers! I'm still working my way through them. My understanding of all things electric is so rudimentary it's gonna take me a while.I'm going to start with the boiling water and just see what happens. I'll update on it.I haven't tested the gauge yet.
I'm deep in the throws of an overhaul (just got back my head from the machine shop - looks gorgeous!), and just decided to take a look at the sensor while i had a few hours to spare.I actually have no idea how to test the gauge either. But was planning on looking it up eventually. Did the test and it seems to work remarkably well. 1,000 ohms of resistance in cold water, and just below boiling point went down below 300 and then down to 100 at a boil.I'll take a look at the gauge when i get back down to the boat.I'd be interested in the answer to the teflon tape query - or using any other kind of sealant when installing the sensor. There are really no threads in my head - but there is still a nice opening that is screws into quite well.
But i believe it was leaking slightly before i pulled it out, and would think some kind of sealant would help me out there. Form-a-gasket sealant maybe? I actually have no idea how to test the gauge either. But was planning on looking it up eventually.Disconnect the wire from the sending unit at the back of the gauge.
Power up the gauge. It should peg low. Short the sending unit terminal on the back of the gauge to ground while it is powered up. It should peg high.Are you OK on testing the wiring? I'll tell you how anyway. Disconnedt the wire at the sending unit and the gauge (already done in your case). Connect a jumper wire to one end.
Run the jumper wire somewhere near the other end of the sending unit wire and lay an ohm meter on the two ends. Should be zero ohms.TRUE GRITEdit: Don't use any kind of sealant. It will add reistance if the gauge even reads at all. I'll let you tell us if the gauge will read higher or lower than the actual engine temp. Dang it Hanley, why do you do that? I completely agree with you!
The added resistance theory would apply to oil pressure as well and I don't hear anyone fussing about that.I think a greater factor with the temp sensor is getting the actual sensing element into the coolant flow. Installing it with a threaded bushing like most of us have draws the business end of the sender out of the flow and with a Tee installed for two senders (temp and alarm) it's completely out.A threaded fitting with no sealant?? Better have a diaper under the engine.
Dang it Hanley, why do you do that? I completely agree with you! The added resistance theory would apply to oil pressure as well and I don't hear anyone fussing about that.I think a greater factor with the temp sensor is getting the actual sensing element into the coolant flow. Installing it with a threaded bushing like most of us have draws the business end of the sender out of the flow and with a Tee installed for two senders (temp and alarm) it's completely out.A threaded fitting with no sealant??
Better have a diaper under the engine.That is exactly why I moved the sensor to the point on the engine that I believe to be the hottest; despite the bushing the probe does extend to the coolant flow.
![How to test a two wire temperature gauge How to test a two wire temperature gauge](/uploads/1/2/5/5/125507727/387270441.jpg)
How to Check a Temperature Gauge & Sending Unit -ChevyHere I check to see if the stock Chevy temperature gauge works by using a potentiometer to see a specific ohms resistance. The potentiometer can be set to mimic the temperature sending unit.
This way you can start to isolate the problem why the temperature gauge does not work correctly. In this case the temperature gauge is reading cold, after the engine has warmed up. To check the water temperature sending unit in the block, I used an ohm meter and wire from the water temperature sending unit to the ohm meter then to a ground. As the engine warms up the ohm meter should show less ohms from the temperature sending unit. The temperature sending unit checked out ok.