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Thread: Strange Coolant Temp Sensor Issue

  1. #1
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    Default Strange Coolant Temp Sensor Issue

    Starting last month, I believed the coolant sensor that had been in the car for years was failing. This is because my car had always been able to cool itself off via the dual Spal fans I have with no issues, then I began to have heating issues. I noticed it was due to the fans not kicking on when my mechanical gauge says they should have been. So after checking things out, the coolant temp sensor was about 20°F off from my mechanical gauge on the A pillar. I had an extra sensor so I swapped it out, the issue is it was also 20°F off and the temperature was bouncing around making the fans cut on for just a second, then it would turn on then off. Fast forward to today, my new Standard Motor Products TX3 sensor came in, I put it in the car and started warming it up. At first things looked OK, MAT was 77°F along with the coolant temperature. As it warmed up I noticed it didn't match my mechanical gauge again and it still bounces around very quickly. When I rev the engine, the temperature seems to shoot up a few degrees then back down. I've verified my mechanical gauge is accurate via infrared temp gun on the manifold neck. Do you guys have any ideas on what to check? Currently, I have the offset at 15° and it seems to be OK, but I just think it's ridiculous that it'd have this issue suddenly. It's set as a Holley CTS. Issues with electrical interference maybe?

    Background: It's a 408W in an SN95. I have a FlowKooler water pump with a new multi-row radiator and dual Spal fans.

  2. #2
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    Default

    Replace the coolant temperature sensor: ACDelco 213-928, Delphi TS10075 or Standard Motor Products TX3. However, I'm surprised the Standard Motor Products TX3 didn't fix it.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  3. #3

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    You can check the CTS with an Ohm meter to see if it's reading correctly. Resistance charts are a Google search away for that CTS.

  4. #4
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    Quote Originally Posted by 95gts5oh View Post
    At first things looked OK, MAT was 77°F along with the coolant temperature. As it warmed up I noticed it didn't match my mechanical gauge again and it still bounces around very quickly.
    This fluctuating temperature seems like clue to me, especially since it just started doing it.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  5. #5
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    Default

    I'll check the resistance today and report back. Thanks guys. It is odd the TX3 is giving me problems.

  6. #6
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    Yeah, if it doesn't start that fluctuating at the trouble temperature (in a pot of hot water & thermometer), then it's not a CTS problem.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  7. #7
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    You're correct, it's not the sensor. I just checked the new Standard Motor Products TX3 and the spare Holley CTS sensor, and they're both fine with steady resistance. I'll check the wiring I suppose. Odd problem.

  8. #8
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    Check your battery/chassis/engine grounding too (first two items below).

    • Ensure the ECU main power & ground is wired directly to the battery. Battery acts as a great capacitor/filter. (LINK & LINK)
    • Cable from negative battery post to engine block, engine block to frame and #8 AWG wire from body to battery. (LINK)
    • Ensure the Switched +12V red/white wire (pink wire - Sniper EFI) remains powered in the "Run" and "Crank" key positions.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  9. #9
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    Seems to be working now. The CTS sensor wire was pinched between an injector and the rail, it had cut the heat shrink so it was likely grounding I guess. I'll replace that section. Thanks guys, it was indeed a wire problem.

  10. #10
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    Thanks for the update. I'm glad you found the problem.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

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