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Touring Motor Gliders Association (TMGA)
discus239

Oil Temp

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discus239

Sometimes during a long climb in hot weather oil temp will creep into the 220"s, then I will level off, reduce power and let it come back down.  I was wondering what relative wind the intake was seeing, so the other day temp reached 223-224, I pulled the cowl flap knob out about half an inch. Temp immediately responded, and in a minute or two went down to 213, no other changes made. Weird, looking at the angle of the door on the ground it is tilted toward closed quite a bit. Can't explain it, maybe someone else can .

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mikeschumann

My oil temp is consistently a LOT lower than that.  It sounds like your cowl flap is not open all the way.  When it is full open, it should be perpendicular to the cowl opening, totally parallel to the air flow.  The cable may need to be adjusted if this is not the case.

NOTE:  The cowl cable needs to be well lubricated periodically or it can be difficult, if not impossible to open the flap after it has been closed.  I use a cable lube tool that you can buy at motorcycle shops, which clamps over the end of the cable and lets you force WD-40 into the cable.  It's a messy affair and takes a significant amount of lube before it comes out by the control knob in the cockpit (make sure you have a rag properly positioned or you will make a big mess).

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discus239

Thanks Mike, when fully open it is correctly perpendicular, it runs cooler when partially (like 20 degrees) closed. Temp only climbs after a long 4-5000ft. + climb so doesn't occur often, I lube the exposed end of the cable and so far always smooth, will perform further analysis.

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mikeschumann

What is the outside air temp and your airspeed when you run into this?  Jim Lee suggested that when you start running hot, you increase your airspeed, which obviously will increase the airflow thru the oil cooler.

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Eric Greenwell

I hope I remember to try partially closing the flap the next time I make a long climb. Could be 4 months before the weather is hot enough to be a problem, and I might forget by then 😉

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Jim Lee

Hey Discus 239, that you Bill?

What you describe is common.  What Mike said about the cowl flap position is correct.  What happens is the cowl flap cable slips in the clamp.  It is attached to the radiator cowl with a clamp.  When the cable housing slips in the clamp, the cowl flap setting changes.  Yours now allows the cowl flap to go beyond open to a partly closed position.  If you take a careful look at the cowl flap in full open position (I know that you already did, but imagine the tail sitting 2 feet high in the flight position) and imagine the air flowing straight into the inlet, you will notice that the partly closed cowl flap will now disrupt the airflow, decreasing cooling.  Pull the cowl flap out one notch and see if the angle looks better.  It doesn't take much of an angle to make a big difference in oil temp during the climb.

Two easy fixes.  Number one, pull the cowl flap knob out one notch and look at the cowl flap position.  If it s now in the full open position, then this is your new open position of the knob.

Number two, measure how much cable movement it takes to put the cowl flap in the open position.  Remove the lower cowling, and move the cable housing this amount in the clamp.  Your open setting will now be correct.

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Andreas Clauss

I have an issue when flying at low ambient temperature. With the aerodynamic efficiency of the plane, altitude restrictions and variable pitch prop, I fly typically at around 2.2 Gal/hour. Very often I keep the cowl fully close at the expense of cabin heating. When I spoke with the Rotax service, they recommended to install a thermostat in the oil circuit.

Any experience with this in the US?

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mikeschumann

Why does closing the cowl flap affect the cabin heating?

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Eric Greenwell

I think the air inlet on the muffler for the cabin heat is in the path of the air flowing through the cowl openings (the ones on each side of the prop shaft) and the oil/water radiators cooling scoop. Closing the cowl scoop reduces the amount heated air from the oil/water radiators, and so less heat gets to the cabin.

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Andreas Clauss

Eric, spot on. 

Are you aware of any U15's in the US with the mentioned thermostat?

Thanks, Andreas

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Eric Greenwell

I've never heard anyone mention a thermostat for the oil on a Phoenix. If you have the original cowl flap with flat section on one of the long sides, it can be replaced with flap that doesn't have that section, and consequently, blocks more of the cowl scoop when it's closed. A downside of the change is a greater chance of overheating if you forget the cowl flap is closed (because it is really much more restrictive than the original flap). I got my new cowl flap from the dealer.

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discus239

Yes, Hi Jim, as always you are precisely correct, adjustment accomplished.

 

Bill

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Jim Lee

We have one Phoenix in the US which has an oil thermostat.  There is an LOA available to anyone who wants to install a thermostat.  It is generally not necessary, in that the cowl flap does a very good job of regulating the coolant and oil temperatures.  The oil thermostat closes to stop the flow of cold oil from the radiator, and then opens again to regulate the oil temperature.  Consequently, the oil temperature fluctuates until the operating oil temp matches the oil radiator (behind the coolant radiator) temperature.  It is better to just wait until the oil temperature comes up to operating temp in both the engine and the radiator.  Usually a taxi to the end of the runway with the cowl flap closed is sufficient even in the coldest ambient temperatures that anyone would want to go flying in.

The cowl flap has no influence on the cabin heat, which comes from a shroud around the muffler.  Exhaust gas temperature to the muffler is what dictates cabin heat which does not change with cowl flap setting.  But a lower operating rpm which Andreas mentions does slightly lower EGT and so would reflect lower cabin heat available.

Try to regulate the oil temperature with the cowl flap so that it is around 190 degrees F.  That is the sweet spot.  If you have a restart after soaring and your oil temperature is low and you are low and about to crash, by all means, use full power to get out of the situation rather than damaging my plane on loan to you.  Don't worry about damage to the engine, it will probably be fine, and the main thing is not to damage my  (your) Phoenix.

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