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Old 09-10-2014, 03:32 PM   #1
DarkObsession
 
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Oil temp gauge calculated?

I think I read on here somewhere (I can't find the thread now) that the stock oil temp gauge isn't actually reading oil temperature from a sending unit but rather is just a calculation based on RPMs, speed, etc. etc. that the computer does? Is this true?

If so, does this mean the transmission temp is also similarly calculated?

Is it possible to rewire the stock gauge to attach to a real sending unit so it shows ACTUAL temperature instead of calculated?
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Old 09-10-2014, 03:39 PM   #2
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From what I recall yes it's a pre calculated temp not an actual temp. The others are real temps.

Hopefully someone with more knowledge can chime in.
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Old 09-11-2014, 02:59 AM   #3
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Quote:
Originally Posted by DarkObsession View Post
I think I read on here somewhere (I can't find the thread now) that the stock oil temp gauge isn't actually reading oil temperature from a sending unit but rather is just a calculation based on RPMs, speed, etc. etc. that the computer does? Is this true?

If so, does this mean the transmission temp is also similarly calculated?

Is it possible to rewire the stock gauge to attach to a real sending unit so it shows ACTUAL temperature instead of calculated?
Perhaps you are thinking of the "Oil Life" display which actually is calculated as you said. However, that calculation depends on real temperatures which are derived from a thermocouple sensor. All your temperature readings are as accurate as the thermocouple, which is time tested and proven, old technology. I think you should trust your guages more than your intuition or "tip of the finger" calculations, (which are about as accurate as the proverbial "butt dyno").

Unless of course you see steam or flames rising from the engine, in which case, you should trust your instincts over the gauges. But more than likely if you do see flames, the gauges will confirm it, and you will shut down and exit the vehicle immediately.
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Old 09-11-2014, 03:29 AM   #4
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I'm curious to see where this thread goes.

I'll admit upfront that I don't really know, but I just can't imagine that the oil temp and tranny temp gauges would show anything but actual temperature read from a sending unit. Temp gauges purpose is to alert you to potential problems before they become catastrophic, I don't see how a "calculated" reading could do that.


I'd like to see some confirmation one way or the other.
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Old 09-11-2014, 11:08 AM   #5
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Originally Posted by yellowz View Post
Perhaps you are thinking of the "Oil Life" display which actually is calculated as you said. However, that calculation depends on real temperatures which are derived from a thermocouple sensor. All your temperature readings are as accurate as the thermocouple, which is time tested and proven, old technology. I think you should trust your guages more than your intuition or "tip of the finger" calculations, (which are about as accurate as the proverbial "butt dyno").

Unless of course you see steam or flames rising from the engine, in which case, you should trust your instincts over the gauges. But more than likely if you do see flames, the gauges will confirm it, and you will shut down and exit the vehicle immediately.

No, I am thinking of the oil temp gauge, present in the SS2.

Here is the post talking about how the oil temp is calculated rather than actually measured: http://www.camaro5.com/forums/showpo...8&postcount=12 (and specifically, here: http://forum.grrrr8.net/showthread.p...l=1#post508830)

The reason I ask is that I went road racing a few weeks ago and pegged my oil temp gauge while doing so (or nearly did). I'd like to add an aftermarket oil cooler but if the oil temps coming from that gauge are estimated rather than read, I need a new gauge too. I'd rather use the stock gauge and just make it do what it SHOULD be doing.
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Old 09-11-2014, 11:11 AM   #6
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Would make sense. If you pull from the sending unit, that is a localized temperature, not the bulk temperature. You'd want to use RPM, fluid flow, and temperature to allow for density corrections.
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Old 09-11-2014, 11:33 AM   #7
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Would make sense. If you pull from the sending unit, that is a localized temperature, not the bulk temperature. You'd want to use RPM, fluid flow, and temperature to allow for density corrections.
The problem with that is that if you add an oil cooler, you won't see any effect because the computer doesn't "know" about it.

I'd rather be taking actual measurements than just letting the computer make assumptions. From the thread I linked, the computer's assumptions can be off by quite a bit in some cases.
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Old 09-11-2014, 11:50 AM   #8
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Originally Posted by DarkObsession View Post
The problem with that is that if you add an oil cooler, you won't see any effect because the computer doesn't "know" about it.

I'd rather be taking actual measurements than just letting the computer make assumptions. From the thread I linked, the computer's assumptions can be off by quite a bit in some cases.
However, the factory doesn't have to take into account that you "added" an oil cooler. That is outside of the OEM built car and the OEM programming.
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Old 09-11-2014, 12:45 PM   #9
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Quote:
Originally Posted by DarkObsession View Post
I think I read on here somewhere (I can't find the thread now) that the stock oil temp gauge isn't actually reading oil temperature from a sending unit but rather is just a calculation based on RPMs, speed, etc. etc. that the computer does? Is this true?

If so, does this mean the transmission temp is also similarly calculated?

Is it possible to rewire the stock gauge to attach to a real sending unit so it shows ACTUAL temperature instead of calculated?
While I don't know the answer to the first part of your question, I do know that it's entirely possible to "calculate" your oil temperature rather than actually "read" it. One of the reasons that the electronic differential in the new C7 Corvette is so effective, is that it varies the amount of lockup based on tire temperatures. But the C7 doesn't have tire temperature sensors. They "calculate" the tire temperatures based on ambient temperatures and tire pressures and it is extremely accurate. I'm sure that they could do the same thing with oil temperatures, using water temperatures and oil pressures. But I don't know why you would think that it's not accurate. If you don' believe it to be accurate, why were you concerned when you pegged your gauge? And why would you think that if you installed an oil cooler the gauge would not reflect the cooler temperatures? If they are using water temperatures and oil pressure to calculate your oil temperature, installing an oil cooler would lower water temperatures slightly and raise oil pressure significantly and this would be reflected on the oil temperature gauge.
And I'm sure that the answer to the second part of your question would be a big NO. Both instrument clusters in these cars are just computer modules on a serial data bus. They interpret data commands sent to them by the PCM and display them as readings on your gauges. In order to change any of this the whole hardware and software systems would have to be re-engineered.
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Old 09-11-2014, 02:19 PM   #10
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Originally Posted by Rocky1974 View Post
But I don't know why you would think that it's not accurate. If you don' believe it to be accurate, why were you concerned when you pegged your gauge? And why would you think that if you installed an oil cooler the gauge would not reflect the cooler temperatures?

http://forum.grrrr8.net/showthread.p...l=1#post508830
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Old 09-11-2014, 02:22 PM   #11
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However, the factory doesn't have to take into account that you "added" an oil cooler. That is outside of the OEM built car and the OEM programming.
Ummm... ok?

Yes, I know it's outside of OEM functionality. I'm not quite sure what value your comment adds.

If I add an oil cooler, I'd like to see ACTUAL oil temps rather than calculated ones that don't take into account that a real oil cooler has been added. The fact that GM didn't plan for it is already known to me and I'm trying to figure out a way around it.
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Old 09-13-2014, 11:37 AM   #12
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Quote:
Originally Posted by DarkObsession View Post
OK, while I didn't read the entire thread, the parts I read raised as many questions as it gave answers. On page 7, he pretty much rules out that the oil pan sensor is a temp sensor, but on page 8 he discovers that it is indeed a oil temp sensor. Why would GM put a oil temp sensor in the oil pan, run wires to it and then not use it for oil temps? Yet he disconnects it and practically every temp and pressure sensor on his engine and his oil temp gauge continues to function. He assumes that the oil temps are calculated, but he never figures out exactly how it's calculated.
If all this is true and there really is an oil temp sensor with wires already ran to inputs on the PCM, perhaps the PCM could be reprogrammed to provide measured temps to the oil temp gauge rather than calculated temps. But again, if this is all true, why GM would not have programmed it that way to start with is beyond me.
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