Temperature gauge needle erratically moving

[dan]

Yupp. It would get to between the A and L of the gauge. 'Normal' temp from how its always ran is between the O and R. So when it started gling towards the hot side, i knew something is off

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[WagonMan]

Fan clutch? When my car was acting funny it was the fan clutch. WagonMan

[Tiggie]

I say stick your aftermarket gauge temporarily to see what’s up. Put the sensor in the original sensor spot, and stick the gauge in a temporary spot visible from the driver seat.

If it’s steady, we know it’s your gauge, sensor, or wiring. If the aftermarket is not steady, we can look into your cooling system.

I have a 95 Ranger that had funky temp readings. It changed very jerkily from cool normal to mid normal range. It was the sender.

[kishy]

I have experienced actual electrical failure of the 90-94 (90-91 Mercury for the silver face) in-cluster temp gauge, however in my case it was pegged to the left. Sender checked out, wire checked out, so I swapped that gauge module out of a junkyard cluster and presto, it worked.

I believe I have literally a pile of these clusters on hand, so if your testing determines the gauge is the problem, I may be able to hook you up.

Also there's an easier way to narrow things down. Get engine to the temp where the gauge is fluctuating. Unplug the wire from the sender. Measure resistance with a multimeter of the sender, between the terminal post on it and the base of it (or intake manifold or other ground). If the resistance reading stays steady and doesn't bounce in the way your gauge is doing, the sender is OK. It could even be a high resistance or loose connection between the wire terminal and the stud on the sender.

Sly, I think that ground block went byebye after 1989, but I'm not completely sure on that. I just know I've never found it in my 91.

[jaywish]

What Wagonman said

Get assistant. Get car to full operating temp. With motor running stare at fan. Have assistant shut off engine. Fan should stop spinning within a second iirc

[dan]

Ok ill check that. And i checked the connection going to the sensor and its on pretty tight

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[dan]

I have experienced actual electrical failure of the 90-94 (90-91 Mercury for the silver face) in-cluster temp gauge, however in my case it was pegged to the left. Sender checked out, wire checked out, so I swapped that gauge module out of a junkyard cluster and presto, it worked.

I believe I have literally a pile of these clusters on hand, so if your testing determines the gauge is the problem, I may be able to hook you up.

Also there's an easier way to narrow things down. Get engine to the temp where the gauge is fluctuating. Unplug the wire from the sender. Measure resistance with a multimeter of the sender, between the terminal post on it and the base of it (or intake manifold or other ground). If the resistance reading stays steady and doesn't bounce in the way your gauge is doing, the sender is OK. It could even be a high resistance or loose connection between the wire terminal and the stud on the sender.

Sly, I think that ground block went byebye after 1989, but I'm not completely sure on that. I just know I've never found it in my 91.

My speedo and odo stopped working so i might be getting a cluster from you soon.

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[sly]

I maybe the grounds were all consolidated to the ring terminals mounted to the driver side body behind the kick panel with the dash change. I know that's where the majority of the grounds are on my 93... behind the kick panels.

[dan]

Ok so strangest thing just happened. Was leaving the hospital on my way home which is less than 10 min away. I punched it to catch a light and my temp was all the way to the A on the gauge. Now i know thats not normal because theres no way it can heat up that fast. Now when i let it off the gas and slowed down a bit it went quickly to the O then went to the middle when i gave it a little gas. Then all the way to A until i got home. Im thinking its a bad sensor.

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[Kodachrome Wolf]

You should be able to use an ohm meter and check the sensor if you happen to have the resistance values it should be at between hot and cold.

Ford didn't change their function much considering I have a 1990 police speedometer with the silver face Mercury temperature and fuel gauges in my '97. I've not had any issues with my gauges, and the gauge has been reasonably accurate.

[kishy]

Check your charging voltage when engine is idling and when revving it. If your regulator is flaky causing voltage to shoot all over the place, resistance based gauges can be inconsistent, changing with engine rpm.

[dan]

At 2400 rpm at 3rd gear was constantly going from N to the L then back to N. in OD was in the middle at 2500 rpms. I dont think rpms have to do with it

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[dan]

So today when i parked at the hospital i heard hissing from under the hood. Popped it open and it hissing around the radiator cap area. The cap is new so my radiator might have a small crack

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[dan]

Problem solved. Pin hole sized cracks on top of the transmission cooler lines. Now my temp is down. Thanks for all the suggestions and advice guys.

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[gadget73]

So the gauge was telling the truth and the car was running hot?