Oil Temp Reading Low

[rockyjs]

I have about 60 hours on the airplane.  For the first 55 hours the oil temp worked fine.  Now it is reading 145 at normal cruise, about 35 degrees low.  Today I turned on the FD 180 and read 70 degrees across the CHT and EGT gages +- 1 degree.  The Oil Temp was reading 62 degrees.  I clamped a wire to the unit and connected the other end to a faston tab on the firewall ground.  The oil Temp still read 62 degrees.  The temperature has never fluctuated, it is just not reading correctly.  Is this a probe problem or something in the EMS unit?

 

[dynonsupport]

Probably a probe problem, though if anything in the wiring or grounding has changed, that's something to look into too. Oil temperature probes, more than other probes, are susceptible to ground problems.

 

[rockyjs]

I rechecked grounding and flew this weekend 4.5 hours. The oil temp reads about 8 degrees low at 70 degrees ambient and at normal operation about 35-40 degrees. The oil temp does move and is steady, just is not reading correctly. Do the probes come with a warranty? I'll need a new one.

 

[dynonsupport]

Can you use an ohmmeter to read the resistance at a known temperature? That will tell us if the probe is off or if it's something else in the system.

We'll replace a probe if it's bad (assuming it isn't multi-years old), but temperature probes almost never go bad, and especially not just by being of a few degrees.

 

[jakej]

I had exactly the same problem - fixed it by running a wire from the sender mount block directly to the ground bus. Hope this helps. ps - we checked the system with a calibrated temp gauge first to confirn the difference.

Jake J

 

[rockyjs]

Thanks Jakej. I did add an additional ground, but the problem remained.

I'll check the resistance with a known temperature and report my reading. I'll also recheck the engine ground.

 

[rockyjs]

Here is the measurements I got on the oil temp probe.

Ambient Temperature - 67

FD 180 Reading:

CHT - 66
EGT - 68
Oil Temp - 60

Resistance reading 644 ohms.  Probe case to ground 0 ohms.

 

[dynonsupport]

None of our oil temp senders should read near 60 degrees at 644 ohms. They'd be between 80 and 90 degrees F. So if your sender actually reads 644 at 67, we'd say the sender was broken, but in this case, the D180 would show 80-90. If just the D180 was broken we'd show the wrong temp, but the measured resistance would be right. The chances of both being broken are basically zero, so I'd say something else is still up.

Did you measure the probe with the EMS connected or disconnected? What kind of engine is this?

 

[rockyjs]

I measured with the EMS connected. I'll disconnect and re-measure. The engine is a Superior IO360. It read correctly for the first 55 hours.

 

[rockyjs]

With the probe disconnected the resistance measured:

Ambient temperature: 60 1.70Kohms
68 1.52Kohms

Thanks

 

[dynonsupport]

But was the displayed temperature closer to 45? If so, and your sensor was bought as part of one of our sensor kits, it does sound like something is wrong with the probe. Give us a call at 425-402-0433, then tech support, for further help with this.

 

[vinhvinh]

I have a ems d120. I have 470 hre on it. 2 of the last three flight show low oil temp ( normally 185 deg and these flight show 155 deg. ) When I download the engine data from the ems d120, it show that in 30 second the temp went from 185 to 155 in 30 second ( my reading are each 30 sec) So my engine was ok and it's probably a ground problem if i read what is in this topic. In one flight, my oil temp was 150 ijust after landing and i turn off my ems and turn it back on and it showed 180

My question was, if my ground is bad, my oil temps will read lower right??. Just want to know before i open my cowling.

thank you

Lan Vinh Do rv-7

 

[Alfio]

I had a similar problem with the oil temperature fluctuation about a week ago. Cleaned the connection to the sender, and put it all back. All fine now for the last 6 hours. Would suggest you do the same before looking into grounding issues.

 

[PhantomPholly]

If there is a weak ground, the temperature will generally read HIGH, particularly with the alternator on.

For those with very low readings, I would suspect a poor connection on the "hot" wire or a faulty probe.

 

[dynonsupport]

As people have said, high temps come from bad grounds between the engine and the battery or the battery and the EMS.

Low temps come from bad connections between the EMS and the sender or the sender and the engine.

 

[vinhvinh]

THANK YOU ALL FOR THESE GOOD INFO.

LAN VINH DO