Oil Temp

[Ratman]

I've been chasing a high oil temp issue that's pretty common in new RV's. I'm hoping to rule out the sensor being bad however, the pressure remains consistent even with high oil temp readings.

Today I measured the resistance across the sensor, then to the accessory case, then to the grounding strap on the engine and finally to the grounding tabs on the firewall. At each location I got 365 ohms. The OAT is 89 degrees and the oil temp, EGT's and CHT's agreed.

Anyone know if 365 ohms at 89 degrees is correct?

Tried to call tech support several times today but only get their voicemail. :-?

 

[aceflyingservice]

I chased this same problem on my Long EZ for a long time. It was determined that the ground to the engine was fluctuating, causing the oil temp readings to fluctuate by as much as 20 degrees. Even a #2 gauge wire run directly from the battery to the engine didn't solve the problem. By turning high amp accessories (strobes, landing or running lights) on or off, I could increase or decrease the oil temp readings.

Obviously there was some sort of grounding issue, but after flying the EZ for 26 years with no electrical problems, I really didn't feel like re-wiring the plane. A simpler solution was to replace the Dynon oil temp sender with the 2 wire sender from GRT. It uses a separate ground wire run directly from the Dynon EMS. This sender is only about $20.00. My oil temp reading is now rock solid and accurate. Maybe Dynon should discard the single wire sender and make the 2 wire sender standard.

Roger Johnson
Long EZ N34JR

 

[dynonsupport]

Where exactly are you measuring Ratman? If the sensor is actually 89F degrees, it should be reading 537 ohms. In contrast, 365 ohms would get you about 107F on the display.

By the way, though our tech support sometimes gets busy throughout the day, leaving a quick voicemail WILL get you a callback between a few minutes and a couple hours.

 

[skysailor]

By the way, though our tech support sometimes gets busy throughout the day, leaving a quick voicemail WILL get you a callback between a few minutes and a couple hours.[/quote]


This quick response and dedication to the customer is just another reason my Glasair panel will have Dynon instruments. I wish my building speed matched their response speed!

 

[Ratman]

Where exactly are you measuring Ratman? If the sensor is actually 89F degrees, it should be reading 537 ohms. In contrast, 365 ohms would get you about 107F on the display.

One probe was on the bolt that the ring terminal is attached to the other was on the body of the sensor. Then from the bolt to te accessory case, then the grounding strap on the engine then to the grounding block tabs. The reading was 365 ohms and only varied 1 or 2 ohms at the different locations.

Thw oil temp was displayed as 89 degrees as did the EGTs, CHTs and OAT. Any ideas?

 

[dynonsupport]

Something's not adding up with your data. At ambient, things are matching, as you want them to, yet you're not getting the resistance values that correspond with the temperature you're seeing on the screen. Are you powered down (you should be) when you are measuring resistance?

By the way, oil temp is usually a grounding issue. Do a search to see some of the other threads on this topic.

 

[PhantomPholly]

I had to run a new ground from my avionics bus to the engine, and even then I had to create a ground strap for the oil temp sender to get things "fixed."  

A barely measurable impedance between the avionics bus and the oil temp sender caused my readings to be up to 50 degrees hot with the alternator on (almost nothing with the alt. off).

Ground Strap for Oil Temp Sender
Ground Strap Mounted on Oil Temp sender

 

[Ratman]

Something's not adding up with your data. At ambient, things are matching, as you want them to, yet you're not getting the resistance values that correspond with the temperature you're seeing on the screen. Are you powered down (you should be) when you are measuring resistance?

By the way, oil temp is usually a grounding issue. Do a search to see some of the other threads on this topic.

How frustrating!

Yes, I know somethings are not adding up. Kinda why I posted the question here. Before I tried to call tech support or posted the question, I searched the forums for oil temp issues and found what you said to be true, it seems to likely be a grounding problem. I also found that this isn't a "new" problem either.

Now, to quantify that problem I checked the resistance at the sensor and then along the path back to the grounding tabs that the entire aircraft is grounded and found that the resistance remains the same no matter where I check it. I even tried two separate ohm meters to rule out the possibility of an error with them (one of them being a very expensive "Fluke" meter). While measuring the resistance there was nothing in the aircraft powered up. All switches in the off position and the D-180 powered down. Actually, when I took these measurements the aircraft hadn't been flown in a couple of days so I could compare all of the other temp sensors.

Now that we agree that there seems to be a problem with the sensor, where do we go from here? I have had suggestions from a few on the forum that I should install a different oil sensor from one of your competitors, should I do that? Is there an alternative that you now provide with the install? Is there an alternative that you recommend?

 

[Ratman]

I had to run a new ground from my avionics bus to the engine, and even then I had to create a ground strap for the oil temp sender to get things "fixed."  

A barely measurable impedance between the avionics bus and the oil temp sender caused my readings to be up to 50 degrees hot with the alternator on (almost nothing with the alt. off).

Ground Strap for Oil Temp Sender
Ground Strap Mounted on Oil Temp sender

Thanks Phantom, finally something I can try. Well, short of installing a new oil cooler anyway.

 

[PhantomPholly]

I had to run a new ground from my avionics bus to the engine, and even then I had to create a ground strap for the oil temp sender to get things "fixed."  

A barely measurable impedance between the avionics bus and the oil temp sender caused my readings to be up to 50 degrees hot with the alternator on (almost nothing with the alt. off).

Ground Strap for Oil Temp Sender
Ground Strap Mounted on Oil Temp sender

Thanks Phantom, finally something I can try. Well, short of installing a new oil cooler anyway.

Actually, the quickest thing you can do is to fire it up, run it until it starts to get warm, and then turn off your alternator. If the temp drops, it is a grounding problem - end of story.

In my case it brought the max temp down from 300 to 240+. Still too hot (and we are re-locating the oil cooler), but no longer reads like the surface of the sun...

 

[Ratman]

I had to run a new ground from my avionics bus to the engine, and even then I had to create a ground strap for the oil temp sender to get things "fixed."  

A barely measurable impedance between the avionics bus and the oil temp sender caused my readings to be up to 50 degrees hot with the alternator on (almost nothing with the alt. off).

Ground Strap for Oil Temp Sender
Ground Strap Mounted on Oil Temp sender

Thanks Phantom, finally something I can try. Well, short of installing a new oil cooler anyway.

Actually, the quickest thing you can do is to fire it up, run it until it starts to get warm, and then turn off your alternator.  If the temp drops, it is a grounding problem - end of story.

In my case it brought the max temp down from 300 to 240+.  Still too hot (and we are re-locating the oil cooler), but no longer reads like the surface of the sun...

WOW and I thought 245 was hot!

Thanks Phantom, it seems really simple until you add in an internally regulated alternator that can't be turned off without damage. Yea, I know my problem BUT, the oil temp sensor should read correctly regardless.

I haven't had the greatest experience with Dynon support thus far and for Dynon to state "Something's not adding up with your data" four days after I posted the question only makes me appreciate people like you and Ace all the more. THANKS SO MUCH FOR YOUR INTEREST AND HELP!

I'll give your grounding solution a try and let you know if it works. What a bummer to invest so much money and effort into a "glass panel" only to have to resort to such a solution as a 50 cent hose clamp.

 

[skysailor]

Ratman,

Perhaps you could still use Phantom's method. Could you start the engine and run it until the temps begin to come up, secure the engine and then restart it right away but leave the alternator off? If you get the dramatic temp drop it should still be a ground problem as the oil will not cool very quickly. Just a thought.

 

[Ratman]

Ratman,

Perhaps you could still use Phantom's method. Could you start the engine and run it until the temps begin to come up, secure the engine and then restart it right away but leave the alternator off? If you get the dramatic temp drop it should still be a ground problem as the oil will not cool very quickly. Just a thought.

While this would work, I would have to do it in flight. The oil doesn't get that hot on the ground. If the sensor is at fault it seems the error get worse and worse as the temps go up. Several time though I have powered down everything after a flight and then turned just the D180 on using just it's internal battery and I haven't seen a significant drop in temps.

I still haven't ruled out the possibility of the oil really being that hot. A couple of weeks ago I flew until the oil temps got into the 240's. I landed and shot the sump with one of those laser temprature guns and the bottom of the sump was 20 degrees cooler than what the D180 was reporting.


I'm going to try Phantoms grounding strap method and see what happens.

 

[PhantomPholly]

I had to run a new ground from my avionics bus to the engine, and even then I had to create a ground strap for the oil temp sender to get things "fixed."  

A barely measurable impedance between the avionics bus and the oil temp sender caused my readings to be up to 50 degrees hot with the alternator on (almost nothing with the alt. off).

Ground Strap for Oil Temp Sender
Ground Strap Mounted on Oil Temp sender

Thanks Phantom, finally something I can try. Well, short of installing a new oil cooler anyway.

Actually, the quickest thing you can do is to fire it up, run it until it starts to get warm, and then turn off your alternator.  If the temp drops, it is a grounding problem - end of story.

In my case it brought the max temp down from 300 to 240+.  Still too hot (and we are re-locating the oil cooler), but no longer reads like the surface of the sun...

WOW and I thought 245 was hot!

Thanks Phantom, it seems really simple until you add in an internally regulated alternator that can't be turned off without damage. Yea, I know my problem BUT, the oil temp sensor should read correctly regardless.

lol - it WILL - if the ground is good.  You can also spend $20 and order the other sort of sender that has two wires.  In my case, all of the wiring had been bundled up and sealed at the firewall, so it was actually easier to fix the ground than install the other type sender.  I did order one, though, so PM me if you want to switch...

Oh, and with the internally mounted regulator alternator you CAN switch the power on and off without damage.  Just make sure you reduce system load to near zero before you move the switch, it will do just fine.

I haven't had the greatest experience with Dynon support thus far and for Dynon to state "Something's not adding up with your data" four days after I posted the question only makes me appreciate people like you and Ace all the more. THANKS SO MUCH FOR YOUR INTEREST AND HELP!

Sorry you've had a bad experience - by and large they are all over things.

I'll give your grounding solution a try and let you know if it works. What a bummer to invest so much money and effort into a "glass panel" only to have to resort to such a solution as a 50 cent hose clamp.

I've still got that other sender if you want it...

 

[PhantomPholly]

Ratman,

Perhaps you could still use Phantom's method. Could you start the engine and run it until the temps begin to come up, secure the engine and then restart it right away but leave the alternator off? If you get the dramatic temp drop it should still be a ground problem as the oil will not cool very quickly. Just a thought.

While this would work, I would have to do it in flight. The oil doesn't get that hot on the ground. If the sensor is at fault it seems the error get worse and worse as the temps go up. Several time though I have powered down everything after a flight and then turned just the D180 on using just it's internal battery and I haven't seen a significant drop in temps.

That right there answers the question. If you shut down the engine and saw no drop in temps, it isn't the ground problem.

I'm wrapping up moving my oil cooler up front of #2 this weekend. I'll let you know how much cooling improvement I get.

 

[Ratman]

Dynon,

I checked the resistance again moments ago. The OAT was 94 degrees in the hangar as reported by the D180. The EGT's and CHT's agreed with that temp as well.

The Oil Temp was reporting 92 degrees. With absolutly everything turned off the resistance was measured at several locations starting on the sensor itself, different locations on the engine and firewall. All were 350 ohms.

I also checked the sensor setup to make sure I had the correct one selected. The sensor is a type 2 and that is what I have selected.

Any suggestions???

 

[dynonsupport]

The ground problem is an insidious one. You generally can't measure the resistance that causes a problem. At 220 degrees, it only takes about 50 mV of error to read 240, and 50mV of error is only 5 amps through .01 ohms. Few multimeters will measure this.

The other problem is that down at 90F, 50mV is less than 1 degree of error. So it's not linear, and it's hard to test unless the engine is warmed up. That's why problems like this always sound like ground issues to us.

The resistance between the EMS and the ground matters too. What kind of panel is this: metal or a composite? We've seen some composite panels need better grounds to the EMS.

One thing you can do to rule out the sender is install a fixed resistor in place of it. A 47 ohm resistor should read about 219 degF. If you unhook the wire from the sender, put a 47 ohm resistor there, and ground it to a good ground, you can then play with things and see if the temp changes. If nothing changes the temp (loads in the plane, alternator, vibration, etc), then the sender might be bad. No idea how it could read right at one temp and not the other, but I guess anything is possible.

It's not always the alternator current that causes an issue. Any load in the plane that shares a ground path with the sender or the EMS can cause this issue.

 

[Ratman]

Dynon,

A 47 ohm resistor got me 223 degrees. I then tried just about every combinations of lights and radios and alternator I could come up with. Many of the combinations that I wouldn't even use in flight. and the 233 remained stable.

I know you were expecting 219 degrees.

Any further suggestions?

 

[dynonsupport]

The 219 vs 223 is probably expected given the variance in resistors. Most resistors are 5% tolerance. The important thing here is that it didn't change at all as you tried things.

Just to check, the resistor was hooked to the same place that the sender was? It wasn't grounded to a different place?

If that's true, then it looks like your readings are right and the real issue is actually high oil temps. The senders are just a material that changes resistance over temperature, so it's not really possible for them to be right at one temp and then not another other.

 

[Ratman]

I have wondered if the same person at Dynon always answers the questions and post on the forum.

In my first post in this thread I said "Today I measured the resistance across the sensor, then to the accessory case, then to the grounding strap on the engine and finally to the grounding tabs on the firewall. At each location I got 365 ohms."

Dynon responded with..."Where exactly are you measuring Ratman? If the sensor is actually 89F degrees, it should be reading 537 ohms. In contrast, 365 ohms would get you about 107F on the display."

So....  It's the sensor, right? No, let's keep looking.

Dynon suggest..."One thing you can do to rule out the sender is install a fixed resistor in place of it. A 47 ohm resistor should read about 219 degF. If you unhook the wire from the sender, put a 47 ohm resistor there, and ground it to a good ground, you can then play with things and see if the temp changes. If nothing changes the temp (loads in the plane, alternator, vibration, etc), then the sender might be bad. No idea how it could read right at one temp and not the other, but I guess anything is possible."

So that's what I did..."A 47 ohm resistor got me 223 degrees. I then tried just about every combinations of lights and radios and alternator I could come up with. Many of the combinations that I wouldn't even use in flight. and the 233 remained stable."

So... It's the sensor, right?

Dynon---"The 219 vs 223 is probably expected given the variance in resistors. Most resistors are 5% tolerance. The important thing here is that it didn't change at all as you tried things.

Just to check, the resistor was hooked to the same place that the sender was? It wasn't grounded to a different place?"

No it wasn't grounded to a different place, it was grounded to the accessory case right where the sensor is installed. Also I used the newly installed ground strap that Phantom suggested. Both test yeilded the same results.

Dynon---"If that's true, then it looks like your readings are right and the real issue is actually high oil temps. The senders are just a material that changes resistance over temperature, so it's not really possible for them to be right at one temp and then not another other."

HUH?!?