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Old 10-22-2015, 01:46 PM   #1
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Default I don't trust my oil temp gauge

I don't trust my oil temp gauge. Short of installing a new sensor, what is the most accurate, convenient location that I could measure oil temps using a laser pyrometer? Looking for temps that I could then ballpark actual oil temp to compare to what my sensor is reading. Sensors is currently located near the original oil filter location on the side of the block. Oil filer is rerouted.

I bought a turbo miata a year ago and I don't trust the old sensor connected to my AIM dash. On hot track days when water temps reach 220, oil is still below 200. As a matter of fact, oil always reads lower than water. Regardless of the conditions. The car does have an external oil cooler mounted on the back side of the radiator. Seem counter intuitive to me that water would be hotter than oil after 25 minutes of very hard driving.

Thanks for your help.
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Old 10-22-2015, 02:02 PM   #2
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Short of installing a new sensor, what is the most accurate, convenient location that I could measure oil temps using a laser pyrometer?
A plastic bucket into which you have drained the oil immediately after stopping the engine.

Seriously, you're not going to get anything resembling an accurate reading by pointing an IR sensor at the outside of the engine.



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Thanks for your help.
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Old 10-22-2015, 02:32 PM   #3
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I know I won't get a comparable temp reading. But was hoping I could take a laser reading, add some base number to represent the temp difference, like 25 degrees, and get a ball park. For example, I have more confidence in my water temp gauge and I can take a laser reading at the same place my water temp sensor is installed and it reads about 20 degrees cooler. I think that is a reasonable temp difference between the actual water temp and the outside of the metal plate the sensor probe is mounted.
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Old 10-22-2015, 02:36 PM   #4
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I know I won't get a comparable temp reading. But was hoping I could take a laser reading, add some base number to represent the temp difference, like 25 degrees, and get a ball park. For example, I have more confidence in my water temp gauge and I can take a laser reading at the same place my water temp sensor is installed and it reads about 20 degrees cooler. I think that is a reasonable temp difference between the actual water temp and the outside of the metal plate the sensor probe is mounted.
Then do that. If your oil temp sensor says 180 and the laser shows 190 near it, you know something is wrong.
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Old 10-22-2015, 03:37 PM   #5
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I've been doing that. Like a gunslinger I've pointed the laser at everything that carries or holds oil. Hottest is the oil filter that reads about 15-20 degrees cooler than my sensor. Does that sound right?

I'm new to this platform. My last track car was a bmw 1M. After a track session oil would be 280. With my miata oil never gets over 200. From what I've read on this form, that is unusually low. Perhaps even a record. Granted I've not done the laser test immediately after a run session. Just after some street driving with water temps about 180 and oil sensor reading about 170. Oil filer laser test would read about 155.
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Old 10-22-2015, 03:48 PM   #6
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I've been doing that. Like a gunslinger I've pointed the laser at everything that carries or holds oil. Hottest is the oil filter that reads about 15-20 degrees cooler than my sensor. Does that sound right?
You're talking to a forum full of guys who install accurate temperature sensors rather than waving lasers around.

Any reading you take is going to be affected by radiant and convective cooling, and to an extent which varies by time, delta-T and the materials involved. There is no correct, universal answer.
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Old 10-22-2015, 04:01 PM   #7
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As stated earlier, new to this platform. That's why I'm asking. New to me car where oil sensor has always read lower than water. Before I install a new oil sensor I thought I would get some advice. I agree that a laser reading will be lower than actual oil temp for all the reasons you've stated.


Or how about I simplify the question. Miata turbo with 205 whp. Run hard at the track for 25 minutes. Oil temp reading 200. Does that sound right to anyone? Anyone else getting oil temps like that?
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Old 10-22-2015, 04:06 PM   #8
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As stated earlier, new to this platform. That's why I'm asking. New to me car where oil sensor has always read lower than water. Before I install a new oil sensor I thought I would get some advice. I agree that a laser reading will be lower than actual oil temp for all the reasons you've stated.


Or how about I simplify the question. Miata turbo with 205 whp. Run hard at the track for 25 minutes. Oil temp reading 200. Does that sound right to anyone? Anyone else getting oil temps like that?
I prefer an oil temp sensor in the oil pan myself.

But to answer your question, I would definitely question those oil temps. The only way I can see them being legit is if you run a huge oil cooler, well ducted, with no thermostat so it's cooling the oil as much as possible all the time.
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Old 10-22-2015, 04:21 PM   #9
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I prefer an oil temp sensor in the oil pan myself.

But to answer your question, I would definitely question those oil temps. The only way I can see them being legit is if you run a huge oil cooler, well ducted, with no thermostat so it's cooling the oil as much as possible all the time.

Thank you. Precisely the kind of answer I was hoping for. It has a small oil cooler, not particularly well ducted, running a 180 degree thermostat. I think I will install a new oil sensor in the oil pan and do some back to back tests. With the AIM I can simply plug and unplug and compare values within seconds.

again, thank you.
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Old 10-22-2015, 04:29 PM   #10
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As stated earlier, new to this platform. That's why I'm asking. New to me car where oil sensor has always read lower than water. Before I install a new oil sensor I thought I would get some advice. I agree that a laser reading will be lower than actual oil temp for all the reasons you've stated.


Or how about I simplify the question. Miata turbo with 205 whp. Run hard at the track for 25 minutes. Oil temp reading 200. Does that sound right to anyone? Anyone else getting oil temps like that?
No insult meant, just telling you that any answer we give (eg: the actual oil temp is going to be XX hotter than what a laser pyrometer reads at such-and-such location) is going to be nothing but a wild-*** guess, because nobody here has ever done an analysis on that.


Given that you are running an external oil cooler, 200F is not totally impossible, particularly if you've installed the temp sensor in a location which is after the cooler. (I don't recall reading you say where the sensor was placed.) If that's the case, it's entirely possible that the sensor is giving you an accurate reading of the oil temperature in a location which does not actually reflect average oil temperature.
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Old 10-22-2015, 04:29 PM   #11
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Thank you. Precisely the kind of answer I was hoping for. It has a small oil cooler, not particularly well ducted, running a 180 degree thermostat. I think I will install a new oil sensor in the oil pan and do some back to back tests. With the AIM I can simply plug and unplug and compare values within seconds.

again, thank you.
No problem. When you get this figured out, bump the thread and post what you found for everyone else to know.

Also, if the temp sensor is cheap and easy to access, you could just try swapping it out for a new one. It's possible the sensor is just bad. Good indication of that would be if the coolant and oil temps are different after a cold soak (car sits for long time) If you hit the key after sitting for 2 days and the oil is still lower than coolant, it's the sensor.
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Old 10-22-2015, 04:38 PM   #12
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No insult meant, just telling you that any answer we give (eg: the actual oil temp is going to be XX hotter than what a laser pyrometer reads at such-and-such location) is going to be nothing but a wild-*** guess, because nobody here has ever done an analysis on that.


Given that you are running an external oil cooler, 200F is not totally impossible, particularly if you've installed the temp sensor in a location which is after the cooler. (I don't recall reading you say where the sensor was placed.) If that's the case, it's entirely possible that the sensor is giving you an accurate reading of the oil temperature in a location which does not actually reflect average oil temperature.
Appreciate it. Not insulted. I'm not smart enough to know any better. Just wasn't getting the type of answer I was looking for. I'm sure I could have phrased the question better. I certainly wasn't expecting any qualified empirical evidence. Just anecdotal from those who can spot a potential problem with minimal data points.

Oil temp sensor is plugged in next to where the original oil filter was located on the side of the block.
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Old 10-22-2015, 05:39 PM   #13
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I have an oil temp sensor in the filter sandwich plate, what's typically considered approaching or at unsafe temps if readings are taken from that location? No external oil cooler. Having a hard time finding an answer searching, sorry for the thread jacking.
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Old 10-22-2015, 05:47 PM   #14
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I have an oil temp sensor in the filter sandwich plate, what's typically considered approaching or at unsafe temps if readings are taken from that location? No external oil cooler. Having a hard time finding an answer searching, sorry for the thread jacking.
Depends who you ask. OEM German performance cars all reduce power and RPM limits around 270-280*F with full synthetic oils. Temps taken at the oil pan. My C63 drops to about 100hp/3,500 RPM limit once it hits 275 or 278, and has to get down in the 260 range before it will go back to full power/full RPM.
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Old 10-22-2015, 05:59 PM   #15
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Depends who you ask. OEM German performance cars all reduce power and RPM limits around 270-280*F with full synthetic oils. Temps taken at the oil pan. My C63 drops to about 100hp/3,500 RPM limit once it hits 275 or 278, and has to get down in the 260 range before it will go back to full power/full RPM.
Yeah that's what I'm struggling with. I'm assuming there's some difference in readings from pan to filter, and a lot of the threads I've found talked about pan temps. In the mean time I'll watch my temps and exercise caution if I'm approaching 280 F. Maybe there should be an oil temp thread
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Old 10-22-2015, 06:03 PM   #16
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Yeah that's what I'm struggling with. I'm assuming there's some difference in readings from pan to filter, and a lot of the threads I've found talked about pan temps. In the mean time I'll watch my temps and exercise caution if I'm approaching 280 F. Maybe there should be an oil temp thread
If several major OEMs all use the same temp range, that's good enough for me. Yeah it might be a touch conservative, but I'd rather make a cool down lap and know I need a bigger oil cooler installed vs destroying an engine. They have to warranty their cars, and those are the limits they run. Good enough for me. Ideal oil temps for maximum oil life are in the 210-220*F range. My C63 targets 221*F from the factory, and 197*F for coolant temps. Surprisingly when pushed hard, coolant temps never budge, but oil climbs up to 250 after a few minutes of hard use.
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Old 10-22-2015, 06:17 PM   #17
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The problem with putting a temp sensor in the sandwich plate, IF an oil cooler is also fitted to the plate, is that you need to know whether the sensor is before or after the cooler in terms of the flow path. This depends on both the design and the installation of the plate.

If the sensor is before the cooler, it will give you a fairly accurate indication which is nearly the same as pan temperature. If the sensor is after the cooler, then it's pretty much worthless. I suspect that this may be the problem the OP in this thread is experiencing, though I haven't yet seen a picture or a truly accurate description of the mounting relative to the oil path.
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Old 10-22-2015, 06:48 PM   #18
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Yeah that's what I'm struggling with. I'm assuming there's some difference in readings from pan to filter, and a lot of the threads I've found talked about pan temps. In the mean time I'll watch my temps and exercise caution if I'm approaching 280 F. Maybe there should be an oil temp thread
The hottest I've seen my 1.6L oil temps on a sandwich adapter were at a 95* ambient track day at Buttonwillow towards the end of a 20 minute session, reaching 260*. Stock power and all, no oil cooler.

I know S2000s reach 280-300* on the track w/o oil coolers (wouldn't recommend allowing those temps). Just like others have mentioned, manufacturers program their cars to go into limp mode once oil temps get hot (370Z comes to mind, it runs hot in stock form)
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Old 10-22-2015, 06:56 PM   #19
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Phil . . . is your sensor on the line going to or coming from the cooler?

If you want to know if the sensor is accurate . . . pull it and put it into a pot of boiling water. Should read close to 212F (adjust a bit for ambient pressures).

Pretty darn easy to see 270F+ on a Miata on track (assuming you drive hard). Oil temp is all about RPM. Oil coolers recommended for track cars.
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Old 10-23-2015, 12:15 AM   #20
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Phil . . . is your sensor on the line going to or coming from the cooler?

If you want to know if the sensor is accurate . . . pull it and put it into a pot of boiling water. Should read close to 212F (adjust a bit for ambient pressures).

Pretty darn easy to see 270F+ on a Miata on track (assuming you drive hard). Oil temp is all about RPM. Oil coolers recommended for track cars.
Good idea Rick. I'm planning an oil change soon and will remove the sensor and dip in boiling water. Here is the best pic I could get of the sensor location. It is the black wire connected to the brass fitting on the block next to where the OEM oil filter was located before it was rerouted to the firewall. Looks like the original owner inserted a "y" fitting between the block and the OEM oil pressure sensor and inserted the AIM temp sensor in the other end of the "Y". The orientation of the pic is not accurate. Best I could do with my big hands and an iPhone. Seems like a good place to get accurate temp readings? What do you think?
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