1991 S10 Blazer digital temp erratic

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Old 11-23-08, 09:19 AM
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1991 S10 Blazer digital temp erratic

Radiator, thermostat and instrument cluster replaced during the past year and working perfectly. Temp display suddenly reading low [150 degrees ], max. Next day erratic, long periods at zero, up and down from normal [195] to zero. Removed sensor, tested with ohm meter and thermometer. OK from 60 to 212. Reinstalled and monitored voltage across sensor with digital volt meter for aprox. 45 min. at idle. At start up display very erratic. Voltage ranging between .982 and 1.34. After a few min., everything stabilized for about 35 min. Voltage varied slowly between 1.049 to 1.66 while display read stable 195. Then display became erratic again while voltage remained in same limits. Has any one had a similar problem and what was your fix? Instrument cluster defective again? Voltage regulator in computer unstable? No check engine so no codes. Thanks, hefe
 
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Old 11-23-08, 12:02 PM
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1991 S10 Blazer digital temp. erratic UPDATE

Checked open circuit reference voltage from computer. Stable at 5 volts. Substituted temp sensor with 2500 ohm variable resistor. Had no effect on display from 10 to 2500 ohms. Seemed to display at random from zero to 200 degrees. Most always at 200. Interesting that it could change idle speed from 750 to 1K. Inclined to think it's the instrument cluster.
Still interested in hearing from any one with similar problem or someone who knows this circuit, as I certainly do not.
Thanks, hefe
 
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