Qs about checking temp w/ infrared thermo, expected readings, thermostat, fan
 

97 SL1

Next round of questions -- what is the best place to check engine temp w/ infrared thermometer, and what temp should I expect to see on a cool day when checking 1) immediately after highway driving, and 2) when idling so long that the fan comes on, right when fan first come on, and 3) right when fan shuts off again?

Background-- I suspect my motor is running too cool in highway driving at least in cooler temperatures. The needle on the temp gauge stabilizes at the 1/4 mark during highway driving at least when outdoor temp is around 30 to 40 F. In warmer weather it stabilizes at the 1/2 mark during highway driving. It seems to always or almost always end up at one of these two positions during highway driving, not somewhere in between. At 0 degrees F driving into a 15-20 mph wind at 60 mph it wouldn't even maintain the 1/4 mark, but I may have had outside air blowing at the high fan setting through the heater core during that test. Does all that seem normal?

Is the thermostat supposed to go from closed to open as the car is warming up at essentially the same coolant temp that it goes from open to closed as the coolant temp is dropping? Or is there typically a significant offset?

Another question that maybe I should ask in a different post, is if I am trying to determine if the radiator fan ever comes on or not, and I'm trying to test by letting the car idle, how high is it safe to let the temp rise before I abort the test, and again, where should I be measuring that? Last summer on hot days I sometimes saw the temp gauge rise well above 3/4, almost touching the bottom of the red, during stop-and-go driving, when outside air temp was around 90 F. A/c was off because not working. I am not completely sure the radiator fan was ever coming on. On the highway in the same conditions the temp gauge was back at the 1/2 (middle) mark and seeming to be quite stable. Outside temp was probably around 90 on the day I saw the highest reading on the temp.

Also, are their reliable ballpark numbers for what 1/4, 1/2, 3/4, (also maybe bottom of red which is about 7/8) on the temp gauge should correspond to in terms of coolant temp, or is that likely to vary widely from one particular gauge to another?

Thoughts?

Thanks --

Gauge:

Remember that the gauge is an indication of what the ECTS (coolant temp sensor) is seeing. That sensor is located in the cylinder head. That's not a big deal, except when the thermostat is closed and the coolant is not circulating in the head an block (with the rest of the coolant in the system).
As for approx temps: you can hook up a real time data capable scanning tool and monitor this in real time, realizing that the gauge movement is damped so that the needle is steady and will therefore be a little bit behind.

Cooling Fan

My 95 SC2 gets between the 3/4 and bottom of the red before the fan kicks on. Always has. IF you want to know if the aux fan is working / functional, jumper the hot lead straight to the batt, the other one to ground just for a second. The more graceful way would be to close the control circuit on the FAN relay

Running Temp
1/4 when warmed up sounds like borderline thermostat stuck open....But it warms up to 1/2 tick in hot weather, so it can't be completely stuck open. Or ECTS funniness.
Have you ever replaced the ECTS with a brass tipped one?

FAN Relay test
To test the fan relay, switch it w the one next to it. They are identical. If the fan turns on, swap them back and ensure the fan is still kicking in,

Thermostat behavior
Thermostat begins to open at 188F.
Thermostat should be full open at 195F.
Note that when first warming upl, the thermostat will likely be opening and closing until the coolant temperature in the block and the coolant temp circulating elsewhere approach the same temp AND that temp is over 195 ish.

Making external temp measurements
If you try to make a measurement immediately after you get off the highway, the vehicle will heat up as soon as you stop b c the cooling from natural airflow has disappeared.
It you try to do the same after long idle, the temp will always be slightly increasing.
The fan kicks in and turns off at the same temp. It's in the Saturn documentation.

I think verifying that this is functioning as designed is more important than single temp readings at given conditions.
That's why the PCM just uses what is an average coolant temp to control the aux fan on and off. Gauge reading means nothing. Pretty sure gauge is also nonlinear. Some mfrs actually leave the needle in the middle even though the temp is fluctuating by 25C bc if thatr was displayed on the dash you'd freak out.

I'd concentrate on ensuring the aux cooling system is fully functional. Then we can tackle the rest.

There is a tiny change that your ECTS is reading completely off low. In his situation, the fan will never turn on bc the temp reading from the sensor never gets to the temp at which the fan is programmed to come on.

Lots of good stuff there, thanks. May take me a while to get on w/ the troubleshooting as car is driveable now but it's definitely on the agenda for sooner or later.

Re "Have you ever replaced the ECTS with a brass tipped one?" -- no

RE "My 95 SC2 gets between the 3/4 and bottom of the red before the fan kicks on. Always has. " -- that's good to hear, maybe my fan is operating normally, will do some of the other checks you mentioned. As of right now I don't trust it enough to leave it idling unattended in warm weather for more than a very few minutes --

Oh, radiator fan should always run whenever a/c button is switched (and interior fan not at 0 setting), correct? If it doesn't, that would indicate a problem, right?

The compressor must kick on for that to happen. If your AC is non functional, it will not occur, even though the light on the switch turns on.

Didn't mention b c you said your AC didn't work.
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Good point, that might have tripped me up. Thanks.