Oil Temp calibration

[aceflyingservice]

According to my recently installed EMS-D10, the oil temp in my Long EZ seemed to be running higher than usual (215-220 degrees in cruise.) I suspected the sending probe, and checked its calibration against a known calibrated and accurate digital thermometer. With the oil temp probe and the thermometer placed in a cup of hot water, the EMS displayed 217 degrees and the thermometer displayed 197 degrees. By the way, water boiling point at my altitude is 210 degrees. Dynon sent me a new probe, however, the results were the same. The OAT, CHT and EGT probes are reading accurately within 1%. Is there an adjustment in the EMS to calibrate the oil temp reading?

 

[dynonsupport]

We have seen high oil temps in non-metalic airplanes such as the Long EZ. On metalic aircraft, the EMS is grounded via pin 3 as well as through its case which is connected to the panel, which is connected to the rest of the airplane ground. In non-metalic airplanes, the EMS is only getting its ground through the small wire leading to pin 3. Since all the current going to the EMS flows through this one wire, even small resistances (milliohms) in the wire cause fairly significant voltage drops (as high as 100s of millivolts). This voltage difference between the EMS ground the engine ground -- where oil temp is measured -- causes the error that you're seeing.

The way to fix this is to install a thick ground wire (16 AWG or larger) from your engine to the EMS. This can most easily be connected to one of the four mounting posts on the back of the faceplate, in between the panel and the mounting nut.

Additionally, ensure that the wire leading to pin 3 on the EMS is as short as possible. This will reduce the resistance in that connection.

 

[Frank Hinde(Guest)]

So I couldn't resist dropping my CHT and oil temp probes into boiling water...CHT probes were almost spot on but the oil temp probe is way off. The EMS say 238F when it should read 212F of course.

Fo the ground I took a fesh 14Ga wire and clamped it wil a big nylon clamp to the side of the brass probe...The other end I tried both clamped to the engine block and to egine ground block firmly bolted to the battery -ve lead.

I am pretty convinced I got a good ground.

This sound like a calibration issue/ batch of incorrect temp probes. I note a lot of RV drivers have been swapping out oil coolers due to "high" oil temps...HAve we found the true cause here?

Can I calibrate the EMS to the probe??

Thanks

Frank

 

[Frank(Guest)]

OH yes if it helps I could easily measure the resistance across the probe at 212F with a calibrated meter if that would help get you a data point?

Frank

 

[dynonsupport]

Yes, getting the resistance at 212F would really help.

Are you sure your water boils at 212F? What altitude are you at? Alititude makes the boiling point go down, so that's not the problem, but it would be good to see what the actual temp should be.

 

[dynonsupport]

The ground you want thickened is the one between the EMS and the aircraft. It sounds like you may have only touched the connection between the probe itself and ground.

There are two measurements that would be interesting to us. With the EMS powered up and the sensor connected, measure the voltage between the Oil temperature output and its case (which is where it is grounded). Also make the same measurements at the EMS connector end, between the oil temperature input (pin 7) and EMS ground (the EMS case works fine for this).

 

[Frank(Guest)]

I am using the supplied EMS wiring harness so i assume I have an adequate grounding wire, plus I am using the Bob Knuckolls method of "super grounding"...I.e all grounds taked to a single brass plate bolted to the battery -ve lead. Besides which all the CHT's are showing accurate. I do agree though the temporary clamped ground lead is the one possible flakey ground, even thoguh it was firmly clamped...Its hard to boil up the whole engine block..

Im at 300 feet.

Do you want those voltages at 212F or ambient?

it will be a week or so before I will be able to get to the back of the EMS..Finishing up "under the hood". i will obtain a meter from work fresh out the calibration lab to get these numbers.

Thanks

FRank

 

[aceflyingservice]

I took your suggestion and ran a 14 gauge wire directly from the EMS mounting stud to the negative battery terminal. A 2 gauge wire runs from the negative battery terminal to the engine block. The oil temp is still running approx. 20-25 degress hot. The additional ground wire had no affect. Any other ideas?

 

[dynonsupport]

Hi Frank,

The prior post actually assumes that you are using our pre-made harness, which has a 22 gauge wire on pin 3. The idea is that on some composite aircraft whose panels don't provide an additional path to ground, the ground wire on pin 3 may not be thick enough by itself. Hence, even though you are using our harness, you still want to make that wire's run as short as possible, and additionally follow the suggestion to run another, thick ground wire (16 AWG or larger) from your engine to the EMS. This can most easily be connected to one of the four mounting posts on the back of the faceplate, in between the panel and the mounting nut.

We'd want the voltages with the oil temperature probe installed in the motor, so that the ground paths are as they would normally be. Ambient should work, but the differences we're interested in would probably be more apparent at higher temperatures.

 

[dynonsupport]

Since a few of you have reported very similar oil temperature inconsistencies, we did some research on our end. It turns out that the characterization for normal Lycoming/Continental oil temperature probe had some bad data in it. This means that if you are using the Lycoming oil temperature sensor, you've been seeing readings that are higher than what the actual temperature is

We've posted a service bulletin to our website with instructions on how to fix the problem.

 

[aceflyingservice]

Thank you for supplying the firmware update to correct the oil temp issue. The oil temp is now reading correctly in my Long EZ. I will send a photo of my installation as soon as possible.

Roger Johnson
Long EZ N34JR

 

[dynonsupport]

We're glad to hear this is working out for you.