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Oil Temp Sensor - False Readings?

gmr

By gmr,
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gmr

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Posted

Hi guys,

I hope this in the right spot..

Am keen to see if anyone has insulated sensors in the engine bay, and how you went about it?

My problem..

I'm having an issue with my oil temp sensor supplied with the Apexi EL2 Gauges. During both relaxed cruising or on the track my oil temp registers at the bottom of the gauge, <50 C.

Engine is a SR20 in a S15 and I'm running a baffled/winged sump and 19 row oil cooler + thermostat. The thermo opens at 84 deg C and has a 5% failsafe. I have a sealed aluminium cover for the oil cooler which is removed at the track. I'm using a brass thread adaptor purchased from Pirtek to fit it into my sump (Apexi use a P1.5 thread??). Oil capacity is about 5.7 L over the stock 3.8 and I'm using 10w40 Martini Sint Eco.

After a good run through the hills or when returning to the pits, I pull up and the oil temp rises to 80-85 C within 2-3 minutes. When the car's moving again the temps are back to <50 C. I don't believe the cooler/sump is causing the oil to cool to <50 C for a few reasons.

a) I understand oil does not change temperature this quickly! There is enough heat to cause pain if I touch the oil filter or thermo.

b) At idle the oil pressure is usually around 180 kPa, after a period at high rpm it drops to around 120 - 130 kPa indicating the oil temp is getting up there.

c) Oil and water temps should be reasonably close. Water temps are around 80 C when on the track, and rise to 100 C in the pits (thick alloy rad and rb25 clutch fan).

d) Went for a drive last Sunday in 30 C heat (hot for Melbourne!) and when I pulled up the oil temp got to 70 C. The clutch fan was engaged.

e) Last oil change I boiled the kettle and tested the sensor, it came up to 100 C on the gauge.

The Apexi sensor (in the pic below) has a long tip which extends into the oil and outside to the harness.

JwCpF.jpg

I think what is happening is the oil temp sensor itself is getting air-cooled when driving and air-cooled by the clutch fan when stationary, and is causing false readings on the gauge.

My friend has the same gauge/sensor in his Chaser, and does not have the same issue however his sensor is taped into oil plate instead of the sump. I've considered doing this but I'm concerned that if the sensor is getting air cooled it will also get heat soak this close to the block. When I researched where to place the oil temp sensor the majority of responses recommended the sump but other than it being the temp of the oil when entering the motor I couldn't find another reason? Would it be better to know the oil temp coming out of the motor?

What am keen to know is if anyone has insulated their sensors and what you used as insulation? Given that the sensor is getting air cooled it would need to be air tight so I've rulled out speedflow fire jacket or similar. Liquid foam was recommended to me?

Am I just better off replacing the apexi sensor with a different sensor, preferabbly sealed? Does anyone know what voltage range the apexi sensors operate over (I'd check but the manuals are in Japanese lol) and do the Greddy or Defi sensors (or other) operate over the same range?

Next year I want to install a Ruzic Engine Monitor II unit, for the guys that are using the EMII what sensors are you using? I'd love to run two oil sensors, one at the plate and one in the sump. Can the EMII do this?

My biggest concern is that on the track my oil temp will get higher than it should and I won't see it on the gauge so I'm very keen to fix this problem! Thanks in advance guys for the advice/info it's much appreciated.

Cheers, Alex

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