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  1. #1
    FEP Senior Member Tigger's Avatar
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    Default Temp gauge acting weird

    I’ve been noticing that my temp gauge has been acting weird lately in my Saleen. All summer it has been between the n and the r. The only time it had gone past the r is when I was stuck in traffic with the ac on on a 100 deg day. Never went past m which is a needle width or two past middle. Not overheating but hotter than it normally is. My commute to work is about 20 miles freeway and about 6-7 miles stop and go each way.

    In the last month or so I have noticed the temp gauge at c like the car isn’t running during my commute. Then other times it is normal. Last week when I drive the car I noticed the gauge at c again when I was close to home so when I got home I popped the hood and jiggled the wires on the temp sensor and tapped the thermostat housing. Nothing changed gauge was stuck at c. Drove the car yesterday and today since the weather was nice. Yesterday on the way to work when I was on the freeway the temp gauge was on the m of normal and it was like 50 deg out. I got to work and I popped the hood. I noticed I lost one of the bolts to the fan shroud. Radiator was full, no leaks. On the way home temp gauge was on the r. Temp was like 60 outside. When I got home last night I replaced the missing bolt on the fan shroud. On the way to work today I didn’t pay attention to the gauge til I was almost to work. I think it was on the o. On the way home tonight I kept an eye on it. Was between n and r most 2/3rd of the way home. Then it dropped to the n for about 5 min. Then it went to c for almost the rest of the way home which was about 7-8 miles. I noticed the needle come up to n about 2 miles from my house for about 30 seconds and then it went back to c. Got home again and jiggled wires, tapped the thermostat housing. No change, gauge was still at C. All other gauges are normal. Oil pressure and gas gauge read normal. No fluctuation.

    So all this leads me to my question on what is going on? I am not sure what is going out. I replaced the thermostat earlier this year. Car has almost 192k. Have not replaced the radiator, temp sender, or fan clutch since I have owned the car which has been almost 11 years. I replaced the water pump and alternator the first week I bought the car. Gas mileage has beeN consistent at 20-21 which I am happy with.

    Not sure where the issue is? Any ideas? Any input would be appreciated.
    Last edited by Tigger; 10-24-2019 at 11:56 PM.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  2. #2
    FEP Senior Member gt4494's Avatar
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    Change the water temp sensor and check the wire for cracks. when all else fails put a mechanical auxiliary gauge some where. You don't want to be driving along thinking things are good and end up with steam out the tailpipes. Trust me!!
    "If you can't explain it simply, you don't understand it well enough."
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  3. #3
    FEP Power Member gmatt's Avatar
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    Sometimes a sticky thermostat will cause the temp gauge to bounce around or the temp sensor is getting sketchy. The factory stuff is not known for it's accuracy, but since there's been a change in behavior, something is up. Otherwise, time to check all that other stuff; rad, hoses, wiring, w.p., etc. But intermittent stuff usually points to electrical/wiring/grounds in my mind.

  4. #4
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    Check your IVR. Headlights on or blower on will cause the alternator to put out a different voltage and the IVR may not by compensating.
    Fox Body/3rd Gen MCA Gold Card Judge
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  5. #5
    FEP Senior Member Tigger's Avatar
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    Drove the car to work today again. Temp gauge came up a couple times to the O but did not stay there for very long before dropping back to C. Headlights were not on on the commute to work and neither was the blower motor.

    I will take a closer look at the wiring over the weekend.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  6. #6
    FEP Senior Member liv2roc's Avatar
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    radiator low on water?

  7. #7
    FEP Senior Member Tigger's Avatar
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    No radiator is full and expansion tank is full at the cold line.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  8. #8
    FEP Senior Member
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    I notice in mine that when I add an electrical load to my car the temp gauge goes way up. It's how I first started to recognize my alternator was undersized. My car will run at the R/M at 12.8volts, but start creeping up to the L if I run my headlights (LED conversion) or the blower. It could just be the wiring not carrying enough voltage, etc. You could also get a laser pyrometer for pretty cheap at Harbor Freight, and when it starts acting funny start checking around the system. It can tell you where it's hot or cold on the various parts.
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  9. #9
    FEP Senior Member Tigger's Avatar
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    Haven’t had a chance to look into it any further but the laser is not a bad idea. I have one that I will throw in the car. Guess my buddy is having a similar problem with his 89 except he has little to no heat out of the heater core.

    I did order another thermostat and a sending unit just in case.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  10. #10

    Default

    On my 1980 replacing the IVR in the cluster and making sure the ground strap from the block to firewall was tight and making good contact solved the erratic behavior of all my guages.

    I was seeing them all creep up randomly and periodically at times. In particular the temp guage would show off the chart hot when it wasn't. At the same time my fuel guage would show higher too.

  11. #11
    FEP Power Member slow84lx's Avatar
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    I have had teflon tape on the threads of the replacement temp sensor keep it from providing a consistent reading on the gauge in the past, and broken wires.

  12. #12
    FEP Senior Member Tigger's Avatar
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    Been driving the car the last couple days since my dad is in town and is using my other car. Gauge still was acting flaky. Gas mileage was down yesterday when I filled it. Car has got ~20-21mpg for a long time. Now down to ~18.5. Been measuring the resistance in the temp sensor when I get home and it has been all over the place. Today I pulled the instrument cluster and played with the IVR. Ford manual says resistance should be 59-61 ohms. I measured .8? Dig out a pinto cluster I have and measured that IVR and got the same resistance. Then I put 12 volts to each of them to see if they pulsated. First time on the mustang one. No pulsing, just got a constant 12 volts. Pinto one was pulsing just fine. Then went back to the mustang one and it started pulsing but it is pulsing faster than the pinto one. For grins I put the pinto one in the mustang cluster. I also changed the temp sensor since the resistance seemed to vary. Upon start up all gauges read a tad lower than before. Once car warmed up the temp gauge came up to N. Drove it around the block and all seemed ok other than my speedo stopped working. Running a pinto speedo cable which is 4-5” shorter so I have to get it back in just right or it will come out. Have to wait for the exhaust to cool so I can loosen the frame mount on the speedo so I can try again LOL. Next few days will be the test to see if gauge is working properly again.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  13. #13
    FEP Senior Member Tigger's Avatar
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    Drove the car to run errands tonight. Temp gauge is still functioning. Oil pressure gauge moves now. It goes down slightly at idle then moves up when rpm’s go up. I filled the gas tank again. Ever since I replaced my sending unit the gauge has always pegged when full and has always read high in my opinion so I never trust it when it gets below a 1/4. Tonight it went to F after filling and did not peg but when I got home. It was down an eighth. I only put 5 miles on it. not sure what to think about that.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  14. #14
    FEP Senior Member Tigger's Avatar
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    Update, temp gauge works all the time now so I think that issue is solved. But I do not like how the gas gauge is acting now. It is opposite of before. Now it drops an 1/8th of a tank within the first 10 miles of filling instead of pegging for the first 100 miles. I ordered new IVR since I do not think the original one is better. I should get that later this week. Hopefully that fixed my gauge issue.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  15. #15
    FEP Senior Member Tigger's Avatar
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    Put in a nos IVR on Saturday. Filled it up and drove it to work today. Fuel Gauge seems to work proper now. Will know more when I drive it again. Not sure about gas mileage though. Dropped a couple MPG and exhaust tips are full of black soot now. I reset the ECU. Probably should have done it when I changed the temp sensor. Hopefully mpg goes back to normal.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

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