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Daox 04-06-2008 09:10 PM

scangauge coolant temp accuracy?
Well, I just installed the new 192 degree thermostat in my Paseo, the stock one is 180. Previous to this the coolant temps hovered around the high 190s, low 200s. So, I got the system all worked out and went for a drive. The coolant temps quickly spiked up over 200 and seemed to hover around 211 (about 12 degrees warmer ironically). So, my current thinking is that the coolant temperature readout from the scangauge is not correct. I further tested this by idling (and some revving) the car in my driveway to get it up to the temp that the fan kicks in at. According to the manual this temperature is supposed to be 201 degrees. Idling the car today it didn't kick in until 216 according to the scangauge. So, I'm thinking the scangauge is off, or my coolant temp sensor is going crazy. Ideas?

SVOboy 04-06-2008 09:23 PM

I imagine the scangauge is as good as the ECT sensor, but I wouldn't know. Interesting problem though.

cfg83 04-07-2008 01:08 AM

Daox -

This is interesting.

I have heard something similar from lovemysan. According to his analysis, the temp sensors are innacurate in Saturns. He found this with the IAT sensor. However, this sensor is identical to the temperature coolant sensor.

I think the SG is reporting what the ECU/PCM *thinks* is the coolant temperature. Therefore, the ECU/PCM thinks that this is the real temprature.

From my POV, it shouldn't matter if the ECU/PCM has been "designed" to work with this type of sensor.

As long as the sensor is working within the original design specs, your car should be ok. If it isn't, however ...


Daox 04-07-2008 10:08 AM

I emailed linear logic to see what they had to say about this.

MetroMPG 04-08-2008 11:11 PM

Let us know if you hear anything. They haven't been as good lately about returning messages (to me at least - a couple in the past few months & no replies).

dremd 04-08-2008 11:19 PM

If you know someone with a GOOD QUALITY Infrared temp gun, borrow it and shoot your thermostat housing, compare to SGII temps . . .

Mine is Dead on with the Infrared gun(with in 1deg F), Not sure if that is helpful or not . . .

Daox 04-08-2008 11:22 PM

I could try that dremd and probably will if I get a chance this weekend.

I did get an email back from Linear Logic. They said...


The ScanGauge gets its information directly from the vehicle's ECU. You may be getting diferent temperature readings from the sensors being in different parts of the coolant system. If the ScanGauge is reporting wrong data, the only way it would be possible is if your vehicle is sending the wrong data to it.

And, since the temp sensor is right next to the thermostat, there will be no variance between what the two see. So, I'm looking at how much a new sensor is. I'd be surprised if it went bad, but its possible.

Daox 05-03-2008 10:06 AM

Well, I got around to replacing my coolant temp sensor last night. The car is still running up to 213 (3 degrees lower) before the fan kicks in... I'd say it could be a bad fan temp switch, but my temps (with the old sensor) got up to 213+ on the highway. I still haven't tried the IR temp gun. I'll probably try that today.

bennelson 05-03-2008 10:16 AM

OK some people might think this is a dumb question, but I am not much of a car guy - What temperature SHOULD a car be at? And does running it a tad warmer make it more efficient?

I pulled the mechanical radiator fan out of my pickup truck and the temp gauge still always reads just a little below the middle. (That INCLUDES my recent trailer towing too!) If it gets hot this summer, I will turn on the Geo Metro electric fan I installed.

Anyhow, can you clue me in on engine temps?

Daox 05-03-2008 10:39 AM

On my Paseo (its different for every car) the temperature should never go beyond 201. That is the temperature the fan is supposed to kick on at. The thermostat temperature is what the car normally runs at. In my case I just put in a 192 degree thermostat. At highway speeds I should be right around 192 then as you don't use a fan on the highway.

The gauge on the car is incredibly inaccurate. I can't tell a difference between 180 and 210 on it.

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