Temperature Gauge Sanity Check

[UserError]

Over the past few days, my temperature gauge has been reading rather alarmingly high while driving, so I borrowed an IR temp gun from work to check what the actual temperatures were. After about 15 minutes of driving normally with no AC, I pulled into a parking lot and the gauge was slightly past the halfway mark. Ambient temperature was 95F, and I have a 75C thermostat installed. On the base of the thermostat housing where the temperature sender sits, I read 168F (75.6C), the upper radiator hose was 160F (71.1C) and the lower was 149F (65C). After idling in place for 5 minutes, the temperature climbed to 175F (79.4C) at the thermostat, and I turned the AC on, which kicked it up to 195F (90.5C). At this point, the gauge was just past the 3/4 mark, though that seems rather high of a position for that particular temperature. Should I just get a VDO gauge with actual numbers on it, or is my car actually outright running hot?

[FLG]

Seems a bit hot with AC on usually they hover a bit past the half way mark.

Is your AUX fan working?

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[UserError]

Aux fan is running, though not at full speed. I'm mostly looking for info on what temperature should be at what gauge reading, to see if my gauge is making any kind of sense.

[FLG]

After re-reading your post....I'm thinking your temp sender or gauge might be off...I don't have any hard info for what temp on the gauge matches the actual numerical value but 195 isn't really overheating.

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[Jaxx_]

my aux fan comes on at 190F and usually the temp gauge is about at 1/2, maybe a sliver above.

This is based on ms2 thermistor curve, however.

[TurboJake]

Upon re-reading that, it sounds fine. ish. It does seem a little high.

IIRC, dead center is 90c. 3/4 mark should be 98c.

[jlevie]

IR thermometers can vary widely. Did you check this one against and object at known temperature (preferably at about 80C)?

The idle rise w/o the AC on sounds like a bad fan clutch and/or a partially clogged radiator. There should not be that much increase in temperature.

[UserError]

We use the IR thermometer regularly, and check it every 2 weeks on average against known 0C and 100C samples, namely ice and boiling water. The fan clutch is a new Behr unit, and engaged less than a minute after the AC was turned on. According to the specs sheet I have for them, they're supposed to engage around 82C, which my car didn't achieve while idling and no AC. If the midpoint on the gauge is supposed to be at 90C, then my gauge is reading rather high.

[dnguyen1963]

When the temp gauge misbehaves the first thing I check is the SI board/batteries or the ground nut.

[Gregs///M]

I confirm your actual temps are ok. I used an IR temp reader and measure the same readings on my M20

However, your gauge should sit around middle mark. Check the grounding nuts behind the gauge as Dnguyen suggested. SI batteries can certainly be a culprit.

[UserError]

Thanks for the info. Guess it's finally time to pull that cluster out and fix the odometer while I'm in there.