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Old 10-29-2008, 12:33 PM   #1
Bob_VT
 
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Water temperature

This has me stumped.

Outside temperature is 30 degrees..... I am using a scan gauge II.

Flat ground with cuise at 55 mph the water temperature is always at 184 degrees. Today since the weather was chilly...... I fllied the heat on at my feet , turned the temp dial to max hot and the fan on 1....... The water temperature goes up to 186 degrees.

I flipped the fan on and turned it off for a few minutes and the temp goes down to 184 but with the fan on it goes up to 186.

I'm stumped. I though turning on the heat would lower the water temperature not raise it?
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Old 10-29-2008, 12:40 PM   #2
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Quote:
Originally Posted by Bob_VT View Post
This has me stumped.

Outside temperature is 30 degrees..... I am using a scan gauge II.

Flat ground with cuise at 55 mph the water temperature is always at 184 degrees. Today since the weather was chilly...... I fllied the heat on at my feet , turned the temp dial to max hot and the fan on 1....... The water temperature goes up to 186 degrees.

I flipped the fan on and turned it off for a few minutes and the temp goes down to 184 but with the fan on it goes up to 186.

I'm stumped. I though turning on the heat would lower the water temperature not raise it?

bob, it will fluctuate , i have my OBDII setup in live mode and the temp oscillates between 183 and 186 degrees. maybe your scan gauge is not refreshing fast enough
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Old 10-29-2008, 03:01 PM   #3
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well by using ur fan ur using more energy isnt it..and that will make the engine run hotter due to more work need to be done... thats just me but i could be wrong..
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Old 10-29-2008, 05:21 PM   #4
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well by using ur fan ur using more energy isnt it..and that will make the engine run hotter due to more work need to be done... thats just me but i could be wrong..
I have considered that and I will test it using the stereo next.
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Old 10-30-2008, 04:16 PM   #5
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The fan should draw considerably more load than the stereo, unless you have aftermarket, I would think. What happens when you leave the fan on but switch the temp to cold (not diverting any coolant to the heater core)? Other than the fact that you freeze?
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Old 10-30-2008, 04:30 PM   #6
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The fan should draw considerably more load than the stereo, unless you have aftermarket, I would think. What happens when you leave the fan on but switch the temp to cold (not diverting any coolant to the heater core)? Other than the fact that you freeze?
Great idea.... will try it.
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Old 10-30-2008, 05:19 PM   #7
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A two degree fluctuation on a 186 deg. reading is about 1%, which is probably less than the accuracy capability of the sensor. Small voltage changes could also cause the fluctuation. Nothing to worry about.
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Old 10-30-2008, 10:24 PM   #8
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Okay I tried it. When the heat gets turned on the temp gauge goes up to 186 on flat ground at a steady 50 mph. Turn the heat off and it drops to 184.

I have been giving this some thought. With the heat on there is more "system" for the heat and it retains a higher temperature. With the heat off there is a faster cooling enabled (a shorter path for the antifreeze) cooling it quicker.

This is all of course valid IF the Scan Gauge and the sensors are that accurate...... +/- a few degrees will not cook an engine.
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Old 10-31-2008, 03:10 PM   #9
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Is that heat with the AC button on?
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Old 10-31-2008, 09:59 PM   #10
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yeah... you don't know how the termastat is working... or not working... a giant factor in how your car controls its temp.
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Old 10-31-2008, 10:48 PM   #11
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Is that heat with the AC button on?
no
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Old 11-01-2008, 04:40 AM   #12
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This has me stumped.

Outside temperature is 30 degrees..... I am using a scan gauge II.

Flat ground with cuise at 55 mph the water temperature is always at 184 degrees. Today since the weather was chilly...... I fllied the heat on at my feet , turned the temp dial to max hot and the fan on 1....... The water temperature goes up to 186 degrees.

I flipped the fan on and turned it off for a few minutes and the temp goes down to 184 but with the fan on it goes up to 186.

I'm stumped. I though turning on the heat would lower the water temperature not raise it?
We could be seeing an artifact of some temperature control that gives higher priority to the internal heater and then lets the radiator cope with the excess. I dimly recall such a system in some GM cars in the past.

Basically the radiator does a more efficient job at cooling, so it drops the temps down to 184. When the heater is turned on it is not as efficient and since it gets higher priority than the radiator, the net effect is to run slightly hotter.

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Old 11-03-2008, 04:17 PM   #13
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I came up with a good explanation.

The temperature of coolant is controlled by a mechanical thermostat independent of the rest of the car. The thermostat is not hooked up to the ECU or anything else so it would not know whether your heat is on or not. However, the temperature sensor is not necessarily next to the thermostat. In fact, base on BobVT observation, the setup must be like this:

temp sensor ---> heater core ---> thermostat ---> engine

Turning on the heater cools down the coolant. The thermostat will open more to compensate, hence increasing the temp at the sensor. This explains the phenomenon.
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