Debugging water temperature gauge

[Al_C]

This is the last hurdle before the body goes on. Consequently, I'm motivated to get this fixed quickly. Maybe you have some ideas?

Background: Gen 2 coyote. Vintage gauges.

Issue: water temperature does not register. No movement on the gauge itself.

So far, I have traced the wire from the sender (which appears to be connected properly) back to the gauge. I disconnected the gauge from the sender wire and plugged in the multi-meter to the connector that goes to the sender. When the car is cold, the multi-meter registers 1 ohm.

Next - start the car. Let it run. Fan comes on. Multi-meter registers 0 ohms. Plug the connector (at the gauge) together, and nothing.

Shut the engine off, let it cool. After 6 minutes or so, the multi-meter registered .2. If I turn the headlights on, the gauge lights up, so we know the light circuit and ground to the gauge are OK.

Possible scenarios:
1. The operator has no clue what he is doing with a multi-meter. (quite possible)
2. Sender is not good.
3. There is a bad connection somewhere along the line.
4. The gauge itself is bad, but I find this highly unlikely.

I appreciate your thoughts and opinions, even if it proves I am an idiot. I just want to get this resolved. Thanks.

oh, btw, I labeled the wires when I first installed them, as the oil sender wire looks exactly like the water sender wire (and they're right next to each other.) the wires plugged in to the water gauge are actually labeled "oil". So why don't I just switch it? They were originally connected to the correct gauge according to my label, but the oil pressure gauge wasn't working. So I swapped them and all of a sudden, the oil gauge looked pretty darn good. So, I concluded I labeled them incorrectly. Heck, this all took place 9 months ago, so who knows! Just thought I'd mention that. There are some things I actually do understand and know pretty well. Clearly, this is not one of them.

[Papa]

I know my gauge takes quite a while to move after the car is running, but if your fan is coming on you probably are past the point that the t-stat is opening. Where is your sensor installed? Something else to consider … the RF harness has wiring for both oil temp and oil pressure. Is it possible you got those mixed up along with the water temp wire?

Here are some more trouble shooting tips: https://www.autozone.com/repairguides/Mitsubishi-Car-1999-05/Coolant-Temperature-Sensor/Testing/_/P-0996b43f8037e980

Dave

[Al_C]

Thanks, Dave. The water temp sender is independent of the RF harness. There are two wires that come off the sender and go directly to the gauge. There are three wires, additionally, on the gauge that are part of the vintage gauge harness.

I didn't do the voltage test indicated in your link. I'll see what I can do with that on Friday.

[Papa]

Thanks, Dave. The water temp sender is independent of the RF harness. There are two wires that come off the sender and go directly to the gauge. There are three wires, additionally, on the gauge that are part of the vintage gauge harness.

I didn't do the voltage test indicated in your link. I'll see what I can do with that on Friday.

It could be that my harness was produced after yours, but mine had sending unit wires for the water temp sensor and a plug (dark blue wire and ground wire) from the dash harness to the gauge for water temp. I also have a light blue for oil temp and gray oil pressure wires. I think the older harnesses had to be wired to the gauges (no plugs).

[CFranks]

The resistance should decrease as the temp increases, take a look at the attached chart, the gauge should start reading 100 degrees at 350 ohms (if you have the speedhut sending unit). Maybe check the units your using on your multimeter when you’re checking the resistance to make sure you’re not in thousands? I’ll go check the resistance mine is showing at ambient tomorrow morning if helpful but it should be over 350.


107374

[phileas_fogg]

Recommend you first make sure the right wire is going to the right gauge.

Like CFranks says, make sure your multi-meter is at the lowest ohm setting when checking continuity of the wires.

Check the oil pressure sender by laying a wrench across the terminals; you should see the gauge pressure sweep upwards. Check the water temperature sensor by holding it in a pan of boiling water (you can bring the pot of water out into the garage); you should see the water temperature gauge sweep upwards. You'll need the key in RUN so that the gauges are powered and these tests will work.

If the wires are good & the sender is good, you almost certainly have a bad gauge. Start & run the car anyway (the coyote ECU monitors temperature for you; don't know about oil pressure though).

My oil pressure gauge didn't work at first. But after I ran the engine a couple of times it magically healed itself, and has worked correctly ever since.


John

[edwardb]

Not ruling out wiring or parts issues. But X2 or whatever on this setup taking a while to show any movement on the water temp gauge. So don't rule that out either. The recommended location for the sender on the Coyote is in an existing port behind the alternator, which I think most of us have used including me. It's actually for an optional block heater. That doesn't matter except that it's way downstream in the coolant flow and basically doesn't have much going past it until the thermostat opens and then what's flowing is the return coolant from the radiator. My Gen 2 cooling fan in #8674, which is controlled by the Coyote PCM and is monitoring cylinder head temp, comes on way before I see any movement in the water temp gauge. On most days, I don't see any movement in the water temp gauge for easily 5-10 minutes when driving. It gradually comes up to about 80 C (176 F), and pretty much stays there. At the same time, the cylinder head temp reading is typically around 195 - 200 F. Interesting read about the Coyote cooling setup FWIW: https://www.diyford.com/ford-coyote-engine-cooling-system-performance-guide/.

[cgundermann]

X3 to Paul...

My custom Speedhut gauge is also very slow to move as well as Dave’s. I thought maybe I had a T-stat stuck open...

I have my water temp for my ECM’s sender located on the passenger side near the thermostat and my sensor for the gauge mounted up front on the driver’s side’s lower intake. The ECM’s digital gauge immediately reads water temp via a OBD2 Bluetooth reader, but the Speedhut gauge takes quite a while to read anything - almost as the T-stat opens. When warmed up for awhile there is a 12 degree difference between both the senders’ readings. Checked external temps at the fittings with an infrared digital temp reader and it supports the difference in water temp readings on different sides of the motor, so I’m not concerned I have any cooling issues.

Chris

[Al_C]

Not ruling out wiring or parts issues. But X2 or whatever on this setup taking a while to show any movement on the water temp gauge. So don't rule that out either. The recommended location for the sender on the Coyote is in an existing port behind the alternator, which I think most of us have used including me. It's actually for an optional block heater. That doesn't matter except that it's way downstream in the coolant flow and basically doesn't have much going past it until the thermostat opens and then whats flowing is the return coolant from the radiator. My Gen 2 cooling fan in #8674, which is controlled by the Coyote PCM and is monitoring cylinder head temp, comes on way before I see any movement in the water temp gauge. On most days, I don't see any movement in the water temp gauge for easily 5-10 minutes when driving. It gradually comes up to about 80 C (176 F), and pretty much stays there. At the same time, the cylinder head temp reading is typically around 195 - 200 F. Interesting read about the Coyote cooling setup FWIW: https://www.diyford.com/ford-coyote-engine-cooling-system-performance-guide/.

Having both Dave and Paul cite the delay in showing movement is significant. I'm using the block heater port for my sender and I have not run the car for longer than 10 minutes at a time. It's also interesting to learn about the differences in temp between the heads and the sender location. The easiest test for me would be to just let it run for a while and see if anything registers. That's the path of least resistance. If that fails, then I'll go back with the multi-meter for ohms and voltage. I should have an update later today!

[Al_C]

They say that patience is a virtue. I wouldn't know that. Or, so it seems. I thank God that I posed my question, otherwise I'd still be going down the volts and ohms rat hole. 18 minutes in, and we have an elevated water temperature:

https://thefactoryfiveforum.com/attachment.php?attachmentid=107389&d=1558106261

Everything looks good (except the clock, but that's easy to correct). All I had to do was let it run long enough. Problem solved. Thank you all for your input, ideas and solutions!

[Jdav]

Everything looks good (except the clock, but that's easy to correct).

Don't be so sure - mine is never correct!

[Jeff Kleiner]

Don't be so sure - mine is never correct!

Then it's like every other Speedhut clock I've seen! Set it today, it'll be wrong tomorrow ;)

Jeff

[edwardb]

Good to hear the temp gauge is working after all. But now I'm feeling left out. My Speedhut clocks have always worked fine. :( Now if they would just light the hands like the other gauges.

[phileas_fogg]

good to hear the temp gauge is working after all. But now i'm feeling left out. My speedhut clocks have always worked fine. :( now if they would just light the hands like the other gauges.

Amen!

[Al_C]

I'll check the clock noon-ish Saturday and see if it stays correct for 24 hours!