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I've been battling this issue for a while. The airplane is an 2005 Ikarus C42B. The Engine is around 1350 hours TT. This airplane was in the rental fleet 8 years ago, then the owner moved it to Florida and I purchased it from the owner in 2020. It has been famous for running too hot in the summertime. 

On a 60F day (18C), from a climb from 2000-3000, My CHT goes up to around 112C, and the Oil temperature climbs to 118C. I know this is in operating range, but remember it is 18C outside and 30C weather is coming to the midwest. 

When picking up the aircraft from Florida, my CHTs were redline and oil temp was near redline. The only way I can get it to cool down is to run around 4800RPM and on the 18C day it drops to 102C CHT and 108C Oil Temperature. Note that this engine has a coolant/oil heat exchanger and not an oil radiator. I'm also running 50/50 Dexcool and not Evans.

What have I tried? Well, everything I can think of:

* Changed sensors - Same results
* Changed engine monitoring to MGL instead of Rotax gauges - Same results
* Checked ground - was good but cleaned it again anyway - no difference
* Improved cowl seal to radiator - somewhat helped but not enough to ease my concern.
* Improved cowl seal to upper cooling fin baffle - no difference.
* Changed the oil pressure spring/ball - no difference
* Tried Challenger permanent oil filter to cool the oil a bit - no difference.
* Pulled vacuum on the overflow bottle to see if any bubbles was in the coolant - none noted
* Idled it for 30+ minutes on the ground - CHT gets to around 88C and Oil around 90C - never above.

I have been talking to Paul at TLAC in the U.K. and he said he has never seen anything like this - even in the summer his experience is they run too cool. I know other owners in the US and they had the same issues I am but mine seems a little worse.

My oil pressure is around 4.8Bar and will drop to 3.5Bar when the oil heats up. Seems to have good oil pressure.

I attached thermocouples to the in coolant/out coolant/in oil at the heat exchanger and noticed that the coolant heated up  about 8C after the exchanger - but this could be bad data.

Things I am going to try next:

* Attach some standoffs (1/2") on the sides of the cowl to open it up a little bit in the back to see if it improves airflow. I did this before, but I became a little nervous about flying it and causing some strange aerodynamic behavior so I didn't fly it.
* Attach a thermal camera focused on the heat exchanger. or radiator during flight. I'm currently trying to print a good 3d printed bracket to attempt this.

I had some discussions with other C42 owners, and one said he had the same problem that the factory replaced his cowl with a newer design and the problem disappeared.

I run 100LL and using AMSOIL synthetic oil currently. I have run Mobil 1 4T as well. 

The carbs are in sync - I am an LSRM-A and I synced the carbs and check them now and then to make sure that isn't the issue

My takeoff RPM in a climb is around 5250 - Flat full throttle is 5600-5700 so I believe I have the pitch dialed in. It was overpitched before but this didn't help

Any ideas what I should try next? I may run a 1/4" tube to an airspeed indicator and attach it to the lower cowl exit to see if there is good airflow.  I've considered removing the radiator and flushing it but I am confused if oil is heating the coolant in the exchanger more or vice versa. Usually a 5C difference between the coolant and oil temperature is standard with this configuration from what I have read.

I do have some exhaust staining near the starter motor (whatever cylinder that is). This seems to be worse after I had replaced the sprag clutch in the middle of Georgia when that failed on me bringing the aircraft back.

Airplane does great in the winter! Never gets up to 90C even on 0C days. Anything about 20C outside and I have to keep my eye on it.

Jim - LSRM-A

  • Re: 912ULS High Oil Temperature

    by » 4 months ago


    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.

     


  • Re: 912ULS High Oil Temperature

    by » 4 months ago


    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.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: 912ULS High Oil Temperature

    by » 4 months ago


    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

     


  • Re: 912ULS High Oil Temperature

    by » 4 months ago


    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?


  • Re: 912ULS High Oil Temperature

    by » 4 months ago


    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.


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