Digital/Analog Oil Temp mismatch
Thread Starter
Racer
Joined: Nov 2005
Posts: 410
Likes: 1
From: Amherst NH
Digital/Analog Oil Temp mismatch
So I noticed today that my oil temp is rising a heck of a lot faster on my analog gauge than on my DIC.
If I turn the car on in the morning (48 degs outside) and allow it to idle for 15 mins my analog gauge comes off the peg to read ~130 but my DIC reads just above ambient ~60. After about 15 mins of easy driving my analog will come up to near operating temp ~170 and my DIC reads ~115. Eventually they will match once the DIC catches up and both seem to be accurate once they do, but what causes this? Im assuming the DIC is more accurate given the "rapid" warm up time indicated by the gauge?
Some notes, the vehicle is TT running an oil cooler with 180 deg thermostatic bypass, and the PCM is swapped with an '03. Car is a '97. No codes.
If I turn the car on in the morning (48 degs outside) and allow it to idle for 15 mins my analog gauge comes off the peg to read ~130 but my DIC reads just above ambient ~60. After about 15 mins of easy driving my analog will come up to near operating temp ~170 and my DIC reads ~115. Eventually they will match once the DIC catches up and both seem to be accurate once they do, but what causes this? Im assuming the DIC is more accurate given the "rapid" warm up time indicated by the gauge?
Some notes, the vehicle is TT running an oil cooler with 180 deg thermostatic bypass, and the PCM is swapped with an '03. Car is a '97. No codes.
Team Owner
Joined: May 2001
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Thread Starter
Racer
Joined: Nov 2005
Posts: 410
Likes: 1
From: Amherst NH
This isn't for the cluster (coolant gauge) this is for a separate oil temp gauge that I've got installed. I should've clarified. Im sure this is simply an issue of the aftermarket gauge sensitivity.
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
As I said, I think it's very likely the difference in sensor quality and/or accuracy between the two. 
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Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Note: He says he has a twin turbo car. It's not surprising he would have a number of analog gauges. Very common.
1/4 mile/AutoX
Joined: Jun 2014
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From: Buffalo Texas
Racer
Joined: Nov 2006
Posts: 297
Likes: 26
From: San Jose California
practical science
If you're really interested, do what we did back in engineering school and put both sensors in the same glass of water and turn on the heat. Then each minute record both readings. When the water boils, see which gauge reads 212 (at sea level) first. If they both track at the same rate, it means that the installed slower sensor is not exposed to the same fluid stream as the other.
Melting Slicks
Joined: Feb 2001
Posts: 2,793
Likes: 355
From: Northville, MI
Part of the problem you are experiencing is the refresh rate of the PCM for the oil pressure PID. Until you reach operating temperature, the DIC should lag a well calibrated analog guage. When I autocross or HPDE, I only have the oil temp showing on the DIC and when I am in the pits you will see the guage refresh about every 2-3 seconds when idling and the fan on high.
Melting Slicks
Joined: Feb 2001
Posts: 2,793
Likes: 355
From: Northville, MI
You can replace your oil pressure sensor location to the oil pan. GM makes a part to attach above the oil filter (replaces the block off plate) and then re route to the gauge and then to the OPS. I might have some pics at my home computer, if I can find them I will post them.
Melting Slicks
Joined: Jan 2008
Posts: 2,590
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From: Nathalie VA
St. Jude Donor '15-'16-'17-'18
Melting Slicks
Joined: Feb 2001
Posts: 2,793
Likes: 355
From: Northville, MI
No, it is the refresh rate the PCM sends information to the cluster and OBD II. If you have access to a good scan tool you can see the changes to Oil temp, rpm, water temp, etc on the scanner as it is refreshed. GM has designated certain PID's (parameter identification) to refresh at different intervals. An example the the Oxygen Sensor may refresh at up to 40 cycles per second, the engine voltage may refresh at 1 cycle/second and the oil temp may refresh at 0.5 cycle/second. Thus every two seconds the oil temp will change until it reaches an equilibrium temp.
Melting Slicks
Joined: Jan 2008
Posts: 2,590
Likes: 48
From: Nathalie VA
St. Jude Donor '15-'16-'17-'18
No, it is the refresh rate the PCM sends information to the cluster and OBD II. If you have access to a good scan tool you can see the changes to Oil temp, rpm, water temp, etc on the scanner as it is refreshed. GM has designated certain PID's (parameter identification) to refresh at different intervals. An example the the Oxygen Sensor may refresh at up to 40 cycles per second, the engine voltage may refresh at 1 cycle/second and the oil temp may refresh at 0.5 cycle/second. Thus every two seconds the oil temp will change until it reaches an equilibrium temp.
Didn't know that. Thanks for the explanation.
Melting Slicks
Joined: Nov 2013
Posts: 2,048
Likes: 315
From: USA
I get that oil temp on the DIC might have a somewhat slow refresh rate... you say updates once every 2 seconds- that seems reasonable and sounds about right to me. The OP is talking about a big mismatch in temps between different gauges/sensors that is taking minutes to finally converge. To me that says something else must be going on or be different-- sensor/probe location differences come to mind.