JDaveSC430

I have an '02 sc430, 60K miles, and wondered if others notice the outside temperature reading taking a long time to register temp. changes? Last week when I backed out of the garage where it's always parked, the temp gauge read 79. Per my phone the outside temp was actually 93. As I drove, the temp gauge still showed 79 for many minutes, then slowly would go up a degree or two and again take a long time to change. It took over 30 minutes of driving in full sunlight on the interstate until the gauge finally registered 91 and I reached my destination. Left it parked outside for an hour and when started the gauge read 96 while phone said actual was 93 still ( that would be normal ). Driving the 30 minutes back home to garage, it did drop a couple of degrees to nearly the right outside temp..
Per my dealer who knows the car well, his research on the issue showed that the temp sensor which is located lower front of the radiator behind the center of the front bumper, and which looked fine btw, primarily serves to send air temps to the ecu for air intake purposes for engine. He said the ecu sends the temp reading to the dash gauge only as sort of an fyi as it is primarily for whatever purpose it serves for the engine. My inside climate control panel was replaced under extended warranty a few years ago for lcd failures and works fine. Tech said therefore the dash unit is simply getting the temp signal from the ecu and the temp sensor doesn't feed the dash unit directly; it's just a convenience side effect from the ecu. Based on how perfectly everything runs, he feels the ecu is operating properly. Engine air filter is clean and clear and all fluids and anti freeze are proper. Car operates as new, just this odd quirk which I hadn't noticed taking this long before. Driving it today, it seemed to register changes faster but still slower than I consider 'normal'. I've owned the car 9 years always garaged and maintained etc.

I know it is far from an exact science just like the mpg reading but 30 minutes to reach approx. the outside temp seemed much longer than usual. Has anyone else noticed a lengthy lag in registering the temp degree changes?

Sorry for a bit of a long ramble; no issues with anything in the engine or radiator or water pump; all is perfect. Just this long lag in temp changes on the dash display.
thanks in advance for sharing any similar experience!,

ivanj

I haven't checked the outside temp specifically but I think the same occurs on my display on my ' 02. My impression: the reading does not change as quickly as that in another vehicle I have in the same garage.Thoughts:

1. Notice also the "Average MPG" at "Average Speed" display takes a long time to change. This is probably also fed by the ECU but has its own averaging algorithm. On another marque I have with a similar display I can reset the mileage. Therefore a car that has been "averaging 20 mpg at an average speed of 30 mph" out of the garage reads "25 mpg at an average speed of 55 mph" when I reset it after finally reaching the highway after 20 minutes or so, putting on the cruise at 65 mph, etc.
The "(Average) Outside Temp" reading may have a similar rule-set.
2. The reading from the ECU may have something to do with many USA bound cars running rich at startup for drivability?
3. Remember these are averaging bits of code. They need many data points to change. (See 5. below.)
4. I suppose there is an electrical test for the temp sensor you mention to see if it is functioning properly. I assume your dealer did not think it was malfunctioning.
5. I would conjecture that the averaging rules for the display are not the same set of rules that the ECU uses to control the engine; the temp display comprises a simple averaging function only. There are more sensors, , e.g., the 4 O2 sensors, involved in the feedback loop to the ECU for engine control, emissions, etc. Hence the ECU for engine control has a more sophisticated set of rules and/or multiple rule-sets. as well it should.

6. Unless your gas mileage has fallen off I would not worry about it. I'm sure that the dealer has an electrical test for the functioning/replacement of that front temp sensor (I have the Service Manual but don't have time to look it up, sorry). Might it be prudent to have it tested and replaced? It is out in a harsh environment but perhaps not as bad as the 02 sensors....have you had to replace any of those? IS there a published MTBF for any of these sensors?
Make sense?

Harold57

The temperature reading has always lagged reality in my car and I'm guessing all SC430s. I'm not sure where the sensor is located but it appears as though it is strongly affected by its surrounding car environment. Once the ambient temperatures have changed outside the car, it takes a bit for the car sensor surrounds to catch up to the change also.

VVTiBob

Location of various sensors related to the operations of the Air Conditioning Systems..... see next comment.

VVTiBob

And here is the explanation of how they interact>>>>

JDaveSC430

thanks to all who replied and thanks for the diagrams; the ambient sensor location is right where my dealer showed me it is and all that info is helpful. It does appear there is varying lag time based on comments from others who have replied here. Just today it seemed to be operating a bit quicker; so perhaps it was a one off the day it took 30 minutes to change!
Greatly appreciate all who took time to provide their thoughts and inputs and great detail; this really is the best forum with the best posters!

Harold57

Very interesting,I never knew that it was so involved. Thanks Bob!