912ULS High Oil Temperature

Hi Jim,

A few point of concern;

I have never been a fan of setting the engines performance on WOT - try for 5200 RPM STATIC. This should give you more RPM on climb out - if fixed pitch prop, you will have to be mindful of Max RPM 5 minute limit. I would preferer to see climb out RPM around 5400-5800 (use pitch to control RPM) I would hope this would reduce the "load" on the engine and therefore liquid temperatures.

The above may reduce your high speed cruise but also reduce fuel consumption/hr.

Rotax 9's are designed to run in the range of 5200-5500 RPM, you will be doing it no favours to run either below or above the recommended continuous operating RPM range.

 "Idled it for 30+ minutes on the ground" Rotax 9's do not like (are not designed) to be subjected to prolonged idling.

I fly in Australia - summer temps regularly get to 45C - its just one more factor that must be managed - higher climb out speed (lower the nose) step climbing, fly early/late in the day, etc Its not unusually to see climb out oil temps get to 120C, just lower the nose, to increase air speed, engine RPM & reduce load on the engine. Cruise temperatures are always under 100C.

I have had the same issues with a coolant / oil heat exchanger setups. We got rid of them and went to a regular coolant radiator and a separate oil cooler. Problem solved. 230F isn’t a big deal. It’s bottom line yellow for oil temp. If during your warmer months it goes over 250F then something needs to be done. Other factors such as oil line bends and prop pitch and air flow through the cowling can be culprits too.  In a big prop study I did years ago I found over pitching the  prop was a big factor, but once you got to a certain level of flatter pitch making it even flatter to have a higher rpm in climb didn’t help any further. The rpm you quoted should be fine as many in the US use those numbers without issue so I would look at another contributing factor. My summer OAT’s where I live can are around 110F right now. Airflow is key and good unrestricted oil flow with that. Personally I don’t care for heat exchanger’s. They just don’t seem to do as good a job as separate coolers and in direct air flow. 

p.s.

Don’t use a full synthetic oil with 100LL. The oil will not suspend the lead and it will be worse for the engine. Use a semi synthetic with 100LL. Auto fuel is fine with a full synthetic.

I hear you about the full synthetic. Currently it has 100LL but I switch to MOGAS over the hotter months. I run about 80% MOGAS,. 20% 100LL. It just happens to have 100LL in it right now because it is a little more difficult to get MOGAS at my field. However, 100LL is very, very expensive right now.

I agree that it needs an oil radiator - but the guy in the U.K. insists he has the same model/year plane running in Spain and it doesn't get hot at all and my airplane is a red herring. I find that hard to believe - because I have flown several of these airplanes and they all run hot - mine just seems to be a little hotter. The airplane is experimental now so I can basically do whatever I want.

Jim

I wrote a repair center in  Germany last summer.. let me show you his reply:

we are Comco Maintenance Station but that`s not main business ! We do maintenance on standard GA and vintage planes, so C42`s is only a side business!

On behalf of your request, we never have seen a C42B with dual oil cooler (air and liquid), so do not have any papers or parts for this!

OAT of 25 degree Celsius is nothing special, normal system must be able to work with this! Please do check on gages first!!!

Your heat exchanger in hooked up in the line from oil tank to oil pump of the engine, temp sensor at the pump. If you really have 125 degree oil temp, this means oil from the engine out and oil tank must be more than this, means +-150 °C! that`s almost impossible! Please check temp on oil tank as well.

On 125 degree water boils, so don`t think your water is that hot! If your water is less than 125° it has the capacity to cool down the oil if plumbing is right!

Check your engine, excessive blow buy heats up and foam up your oil! Tank vent is ok? Clogged exhaust can course same systems!

If you have any kind of thermostatic valve, remove all of this and fly with standard routing of plumbing oil and water independent!

If all of this doesn´t help ask Comco for a desert or tow conversion of C42B, but don`t know this exist or oil temp out of range ever is been an issue to think about?

Roger Lee wrote:

I have had the same issues with a coolant / oil heat exchanger setups. We got rid of them and went to a regular coolant radiator and a separate oil cooler. Problem solved. 230F isn’t a big deal. It’s bottom line yellow for oil temp. If during your warmer months it goes over 250F then something needs to be done. Other factors such as oil line bends and prop pitch and air flow through the cowling can be culprits too.  In a big prop study I did years ago I found over pitching the  prop was a big factor, but once you got to a certain level of flatter pitch making it even flatter to have a higher rpm in climb didn’t help any further. The rpm you quoted should be fine as many in the US use those numbers without issue so I would look at another contributing factor. My summer OAT’s where I live can are around 110F right now. Airflow is key and good unrestricted oil flow with that. Personally I don’t care for heat exchanger’s. They just don’t seem to do as good a job as separate coolers and in direct air flow. 

p.s.

Don’t use a full synthetic oil with 100LL. The oil will not suspend the lead and it will be worse for the engine. Use a semi synthetic with 100LL. Auto fuel is fine with a full synthetic.

Hi Roger,

As usual I agree with almost everything you have said (above) except the 1% to do with propeller pitch, therefore climb  rpm and engine load.

Sure, if pitch gets too fine/flat there will be negligibly improvement, however Jims problem (hot weather & concerns about high engine oil temperature and his statement ".....takeoff RPM in a climb is around 5250 - Flat full throttle is 5600-5700 .." strongly suggest the prop pitch is over course, which leads to a labouring engine, higher temperatures and although he doesn't give airspeed and climb rate data, may negatively impact on engine cooling.

I would go further and say that it looks like Jim has "tuned" his engine for what he considers an ideal WOT despite Rotax instruction to tune for static rpm.

Much depends on aircraft design,weigh, load and prevailing temperatures but in general static rpm is the safe way to tune a prop (not WOT). Why? because the highest load experienced by the engine is in the take off /climb out phase - this is where the engine is under most stress, therefore the the phase prop & cooling system should be configured for - not WOT at cruise.

Of course my argument fall in a heap if the aircraft owner is unconcerned with engine service life.