Operating temperatures for Rotax 912 ULS

[Dave C]

Yesterday I took a couple flights in my Evektor Sportstar (Rotax 912 ULS). On both climbouts the CHTs both hit 230F which is the end of the green/ beginning of the yellow. The oil temp was about the same. They seem to have stabilized at that value during the climb (~5000 rpm, 65 kt). After leveling off the temp reduced to 220F in 5000rpm 90 kt cruise. It was not hot outside. The outside temperature on the ground was about 70F and it was cloudy (250-600 MSL). Cruising altitudes were 3500 and 4500 MSL.

There was sufficient coolant in the expansion tank. The oil level was full. When checking the coolant cap on the top of the engine it was not full to the absolute top. It was about 3/4" below the sealing surface.

Should I be concerned about the temperatures? In the past I haven't watched my gages as close as I do now. I more just checked that everything is in the green and not remembering the values. Any thoughts?

-Dave

[3Dreaming]

How fast does your engine turn full throttle level flight?

[Warmi]

This Sunday I was flying in my Sting with OAT being close to 70 .
A longish climb out resulted in around 215F CHT , later stabilizing to about 205F or so.

This is all normal for me since I start noticing CHTs in yellow and need to start managing my climb outs somewhere above 85F OAT.

[Dave C]

How fast does your engine turn full throttle level flight?

About 5500 rpm

[3Dreaming]

Just a few observations. One you might be just a little over pitched on the propeller. Second you could possible increase you speed during the climb to allow more cooling air. That is of course if you don't have terrain to clear. Lastly is to bump up your RPM in cruise flight. The Bing carburetors tend to run leaner in the mid range. I have experienced temps going up as you slow the RPM below 5000 in cruise flight. Also check to see if any baffling or ducting is cot in position for the oil and coolant radiators. Also make sure any tape for winter operations has been removed.

[drseti]

I noticed something similar last Friday in my SportStar, with both of my students. OAT around 70, oil temp hitting the bottom of the yellow in climb. Returned to normal on leveling off. CHTs normal. Fluid levels normal. I wouldn't be overly concerned - if temps keep creeping up, a shallower climbout (75 knots or so) will cool things right back down.

[Dave C]

Just a few observations. One you might be just a little over pitched on the propeller. Second you could possible increase you speed during the climb to allow more cooling air. That is of course if you don't have terrain to clear. Lastly is to bump up your RPM in cruise flight. The Bing carburetors tend to run leaner in the mid range. I have experienced temps going up as you slow the RPM below 5000 in cruise flight. Also check to see if any baffling or ducting is cot in position for the oil and coolant radiators. Also make sure any tape for winter operations has been removed.

I'll certainly do some more checks as you suggest to see if I find anything. I have wondered about the pitch. Statically at full throttle or at the beginning of a takeoff the rpm is about 4900. I guess for best climb it should be >5500.

[Dave C]

I noticed something similar last Friday in my SportStar, with both of my students. OAT around 70, oil temp hitting the bottom of the yellow in climb. Returned to normal on leveling off. CHTs normal. Fluid levels normal. I wouldn't be overly concerned - if temps keep creeping up, a shallower climbout (75 knots or so) will cool things right back down.

That is good to know my setup is not way off the mark. I am a bit concerned about what happens when the OAT is 25 degrees hotter.

[3Dreaming]

Just a few observations. One you might be just a little over pitched on the propeller. Second you could possible increase you speed during the climb to allow more cooling air. That is of course if you don't have terrain to clear. Lastly is to bump up your RPM in cruise flight. The Bing carburetors tend to run leaner in the mid range. I have experienced temps going up as you slow the RPM below 5000 in cruise flight. Also check to see if any baffling or ducting is cot in position for the oil and coolant radiators. Also make sure any tape for winter operations has been removed.

I'll certainly do some more checks as you suggest to see if I find anything. I have wondered about the pitch. Statically at full throttle or at the beginning of a takeoff the rpm is about 4900. I guess for best climb it should be >5500.

With these slick airplanes that have the prop pitch fixed for flight you have to find the best overall setting. The airplane will have the most reserve horsepower for climb if the engine is turning 5800 RPM. Now you can only use this for 5 minutes after takeoff. The problem is if the prop is set to have that RPM in climb, then it will easily overspeed when you transition to level flight. Now Rotax would like to see at least 5200 for climb out, and likely you could still overspeed with that setting with a slick airplane. With the Flight Designs it has generally been decided by group consensus that if you set the RPM to 5550-5650 full throttle level flight at the altitude you normally operate at it is the overall best setting. Over pitched can lead to damage on the engine, and under pitched can put you in a range of the carb that will generate higher EGT temps.

[Sling 2 Pilot]

I’m on the opposite side of the spectrum. Flew yesterday, ambient temp was 83F @ FL030 and I had forgotten to take aluminum tape off both radiators, oil temp was no higher than 179-183F. Coolant was 149-172F. I’ve yet to get anywhere near 200+F oil temps in 3 years of owning my SLING 2.

[Warmi]

Are you sure your sensors are ok ?

Unless you flying without a cowling that’s seems odd to me not to see the temp going over 200 , even in the middle of the summer ..

[3Dreaming]

I have been flying a Tecnam P2008 some, and the temps run cool on it as well.

[David]

Today 89 deg and humid this afternoon in PA. Temps on two RV12 are very close at 223 on steep climb out and leveled off at 3500 leveled off at with temps around 215. Sorry I didn’t get the OAT at altitude. One of the RVs is stock and mine has a big bore kit and I run about 1 deg hotter than the stock 912.

[Sling 2 Pilot]

Are you sure your sensors are ok ?

Unless you flying without a cowling that’s seems odd to me not to see the temp going over 200 , even in the middle of the summer ..

Checked with another Sling owner after posting and he is seeing the same temps as I.