High Engine Oil Temps.

[mike.smith]

OK, now that we know the actual temps, yes, that's way too high. Please let us know some info like:
- Top or bottom mounted oil cooler?
- Opening in the lower front of the cowl, per the Sonex plans?
- Where is the oil temp sender installed?
- What do CHT's run in flight?
- Running the Sonex recommended oil (which one?)?
- Oil filter, or just the stock screen?
- Any other things about the oil or cooling system that are not per the Sonex plans?
- What is your oil pressure in flight?

[Cpt.tidy]

I'll check it out this weekend provided we don't get hit by the hurricane. The following is a list of answers to your question;
1. Top mounted cooler
2. OneX, opening in the top of the cowl.
3. Pilots side, forward middle of engines.
4. I'll check, but no limits exceeded.
5. yes on the oil
6. Stock screen
7. Per the plans.
8. Oil pressure was in limits.. But will get the exact figures next flight.

In addition, we have had extremely hot days of late. Temperatures as high as 97 degrees Fahrenheit. I am beginning to believe this may be the culprit.

Thanks for your post reply,

CPT Tidy

[tx_swordguy]

I know the high OAT will effect the ability for cooling the oil however that in and of itself should not be the only culprit. If you change your oil I would blow out the oil cooler with compressed air to make sure you have no sludge that is blocking the cooler from the inside. If this is a new occurrence that may help. If the problem has been there it may have to do with your air flow through the cowling. Opening up your exit a bit and making sure your baffling is tight will help with that. You stated your temp is normally less than 220. even 220 is getting up there for normal cruising so if you are running 218 all the time I would be wanting it down closer to 200 but that is me.
Mark Whiddon

[mike.smith]

It's interesting that the Onex doesn't have a bottom cowl opening (at least none that I saw). On the Sonex, even if you have the top-mount oil cooler (as I do) Sonex recommends leaving the lower cowl opening to get air running under the oil sump plate. When I moved to the top-mounted cooler I tried completely closing the lower opening with a plate. The oil got up over 200 deg. So I have a plate just partially blocking the lower cowl opening. Even on very hot days I don't see temps over 170 deg F. Normal cruise is around 150-160 deg F.

[Rynoth]

Is the consensus here that 230 degrees is too hot (despite 240 being the max)? My aerovee turbo has been running in the 210-220 range (stock setup, top cooler, no lower opening in cowl.) I didn't believe mine was running any hotter than normal. Also this is on hot days, 90+ OAT on the ground.

On the Sonex, even if you have the top-mount oil cooler (as I do) Sonex recommends leaving the lower cowl opening to get air running under the oil sump plate.

When I asked (in 2015), I was told by Sonex that the lower cowl opening is for a bottom-mount oil cooler is unnecessary if running a top-mount. Here is the quote I was given: "Having the lower opening in the cowl when the top-mount oil cooler is installed is a matter of choice. Our turbo airplane had the opening, but that’s only because it had it before the turbo was installed. Our Waiex doesn’t have the opening (although it’s not a turbo – yet)."

Furthermore, I have "heard" that higher oil temp readings may be a result of the temperature sensor itself(mounted on the forward-left-bottom) might be getting hot and running a little air over it may result in lower indicated oil temp, even though this probably doesn't change the actual temperature of the oil itself much.

[mike.smith]

Is the consensus here that 230 degrees is too hot

In my opinion, yes. But others may have another opinion based on their own experiences, so it would be interesting to hear. Right or wrong I've considered going through 200 deg to be the point at which I want to start doing something, or being concerned. Maybe that's unfounded, I don't know.

Furthermore, I have "heard" that higher oil temp readings may be a result of the temperature sensor itself(mounted on the forward-left-bottom) might be getting hot and running a little air over it may result in lower indicated oil temp, even though this probably doesn't change the actual temperature of the oil itself much.

I've thought about that, and there may be some truth to it, but on my installation the probe is in the bottom of the oil sump plate, and the probe itself is up inside the oil, not out at the surface of the bottom plate where the air is. So I'm not convinced there's much cooling of the probe from air flow.

It would be interesting to hear about other's oil temps with the temp sensor located somewhere else on the engine.

[WesRagle]

Hi Guys,

Where I live it's hot a good portion of the year. There is only one escape from the heat, climb.

Having said that, I like my oil temp in cruise to stay at or below 200 Deg. F. That gives me a reasonable margin when I need to climb to cooler air.

Wes

[MichaelFarley56]

For what it's worth, I'll use my airplane as an example of the necessity of cooling air going over the sensor for proper indication.

Last fall, as I rebuilt my AeroVee I installed a brand new, horizontal split cowling but I never installed the lower oil cooler "smile" slot that allows air to go over the engine sump. As the air temp warmed up this spring and summer, I was getting indicated oil temps in the 230 range which was a lot higher than my engine has ever indicated before (my original cowling had the lower cowling opening). I was still getting good oil pressure (around 48-50 psi) and suspected I was having an issue with the oil temp sensor getting heat soaked by the exhaust and hot, stagnant air in the lower cowling.

In order to test this theory, I cut a small notch in the metal baffling, (close to the oil dipstick) just behind the cooling air inlet on the pilot side and bent the metal a little bit in order to create a small ram air opening that would hopefully force cooling air over the sensor. I made no other modifications and saw no changes in the oil pressure, but the oil temperature indications immediately dropped from 230 to 200. Obviously, getting a little bit of air flowing over the sensor made a big difference on my engine readings!

If you're struggling with high indicated oil temps and you don't have the lower cowling opening, you can consider either adding the cowling opening or modifying your baffling (or adding a blast tube) by the temp sensor and see if that helps.

Remember, oil pressure is important to monitor as well. As the oil temp actually goes up, the pressure will probably drop, so watch out for the oil pressure. Finally, I know VW engines traditionally run low oil temps but remember you actually want your oil to be above 180 degrees (200 or so is ideal) so any water is boiled out of the oil.

Good discussion!

[WesRagle]

Hi Guys,

I assume that we are all talking about a sensor like this:


I've never cut into one of these but I assume (I'll do a lot of that in this post) that there is a thermistor connected between the terminal on top of the sensor and the sensor body.

Notice that there is no thermal barrier between the "nut and threads" portion of the sensor and the portion of the sensor that is immersed in oil. That leads me to believe that for the sensor to indicate correctly the mass that the sensor screws into (and the top of the sensor for that matter) need to be at the same temperature as the liquid that the tip is immersed in. Since (during operation) the under cowl temperature is lower than the oil temperature, I would expect the sensor to report a slightly lower temperature than actual oil temperature even with "static" air.

Blasting the sensor will cool air will cool the top of the sensor and the metal in the immediate area of the sensor threads. Again, with no thermal barrier, it will cool the sensing element as well causing a "too low" indication.

I guess what I'm trying to say is that blasting the sensor with cold air to lower the oil temperature indication eerily reminds me of moving a CHT sensor to lower CHT readings.

My Thoughts,

Wes

[mike.smith]

I've never cut into one of these but I assume (I'll do a lot of that in this post) that there is a thermistor connected between the terminal on top of the sensor and the sensor body.

Notice that there is no thermal barrier between the "nut and threads" portion of the sensor and the portion of the sensor that is immersed in oil.

While it's hard to find cut-aways of such a simple device as a temperature sensor, from the things I've found the outside only "looks" like it's a solid mass, but in fact there are separations between materials. These links may not be exactly what we have in our engines, but they are at least similar. And it looks like the engineers were smart enough to have thought to separate the actual probe element from the rest of the body:
https://www.youtube.com/watch?v=TC7iTRWZ0bM
https://www.slideshare.net/HardikRathod ... re-sensors
http://premierautotrade.com.au/news/exh ... rs-EGT.php (see EGT cut-away near bottom of page)