Oil temps

by Andy Owen in General Tech Discussion 9 years ago

Rans s6. Now the weather is getting warmer (over in the UK) I have noticed the oil temp getting hotter, typically 110C at level flight, in the climb starts rising, at 120 DegC I back off to level or I assume it would keep going, then it comes back down To 110C, The rpm was not reaching the 5.8k at WOT so I have taken a small amount of pitch out of the prop, it is now revving to 5.2K no the ground, due to the weather I have not tried it in the air yet, hopefully it should be nearer to the max revs at WOT level flight.I am hoping this will help the oil temp a little. I have noticed that the oil cooler (9 row) is located under the engine and doesn't seen to be in a direct airflow, the engine cowling is he sheet metal variant so it would be easy to cut an opening just in front of the cooler,
My question is what oil temps are you getting and I are the temps I'm getting unusually hot,my engine is 80 hp 912, any other suggestions would be appreciated.
Andy.

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Re: Oil temps

by Roger Lee » 9 years ago

Roger Lee

126 5.14k 4.61k

Hi Andy,

This answer varies a lot from plane to plane, but climb out temps
I have to smile a little at what the high temps in the UK are. In the southwest US it is already 35c+ and rising and we'll see 40c soon and your current temps are my dead of the winter temps.
Hi Andy,
They have Rans S6's here in my area and they don't get that hot.
Back to your question. Climb temps with a direct airflow over the coolant and oil coolers can be anywhere from 180F cool (not cold) morning and up to 240F on a hot (240F) day with a heavily loaded plane for some. I never see over 230F on a hot day in my plane.
These temps are influenced by, OAT, prop pitch, airflow over the coolers, type of coolant used (Evans vs a 50/50 ratio) and take-off technique (steep vs shallow) and even hose routing. If the hose routing makes too tight a bend then the hose may not kink, but reduces its radius enough when hot to slow oil flow which then helps raise temps.

With your OAT I would say that your 230F temp is a tad high and 248F is really too high.

Under warm OAT the 230F could be perfectly normal depending on the engine and prop setup, but 248F is too hot. Even the 230F for me would be too warm with your OAT this time of year

Since you brought up prop pitch I would set it (if only ground adjustable) to get around 5600-5650 WOT at your average altitude in flat and level flight. Don't worry about static or anything else since it isn't an in flight adjustable pitch prop.This pitch should give you the best BALANCE of climb, cruise, WOT and fuel economy. Making a prop pitch too coarse or too flat may be part of your problem. If you have a prop pitch set to get 5800 rpm at WOT in level flight then you have a good climb prop and this will cut into your fuel economy, cruise speed and raise oil temps. If you have a specific need for a climb prop setup no problem. The big part as you mentioned could be the indirect airflow over the oil cooler. I know some that fashioned a scoop and put it in place to give the cooler more forced air which can have a tremendous effect on lowering oil temps.
If you are getting 5200 rpm static on the ground that's too flat (climb prop). Don't worry about static go fly and tune it for WOT in flat and level flight. Static only gets an unknown prop in the ballpark and you're already there so setting up for actual flight, altitude and plane configuration is what you need to do.

Do this first then take another look at oil temps. Then you can work your way through and see what the issues really are. It may be one thing or a combination of the above things causing high oil temps.

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

Thank you said by: Andy Owen

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Re: Oil temps

by Andy Owen » 9 years ago

Andy Owen

6 9 0

I have taken a small amount out of the prop, that helped bringing the temp down by a small amount, she now revs to 5.7k WOT level flight. I then opened up an air scoop under the cooler, the oil temp has come down by 10 deg C across he board. In level flight she sits at 100c now. The cooler has seven elements I am thinking of going for a larger item with a couple of extra elements.
The other thing I have noticed is the plugs seem to be a little whiter than I would like so I may drop the needles one notch,

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Re: Oil temps

by Roger Lee » 9 years ago

Roger Lee

126 5.14k 4.61k

Hi Andy,
A 10c (40F) drop is pretty good.
100c or 212F is not a bad place to be. If your needle is in the #3 position I would leave it and if it isn't you may want to put it back. Do you have EGT's? I wouldn't play with the needle without all the info. The whiter plugs may be fine and you may just not be used to that. At 5700 you are still leaning on a climb prop pitch, but it isn't bad. You could certainly leave it there. if you like to tweak a bit take out about .25 degrees more. That should put you around 5600. This is strictly a personal preference and only if you want to experiment a tad more with rpm verses performance. The difference between 5600 and 5700 won't be a lot, just a small amount.

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

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Re: Oil temps

by Rhett Mitchell » 9 years ago

Rhett Mitchell

8 99 0

100C is great! Dropping the needles will lean it more....I think you have got it the wrong way around?
If the plugs are black, you drop the needles leaning it out.....

And not to hijack the thread but.... :evil:
Do you think the same about thick wing/STOL aircraft Roger in regards to 5600 WOT rpm?
I know you're a CT flyer and was reading a post from you, from 2011 to a Alegro pilot recommending the same thing (5600).
My STOL type A/c is pulling 5800 WOT. I don't really need a severe climbout as I fly from the bitumen..
I'm struggling to get much past 90kts pulling 5400-5500....
Do you think going 1/2 a degree coarser will help the cruise speed?

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Re: Oil temps

by Andy Owen » 9 years ago

Andy Owen

6 9 0

Yes sorry I meant to say drop the clip one notch that would lift the needle up. Out of interest I think first I will check the fuel hight in the float chambers, I would imagine that would have an effect on the mixture, can you tell me what hight it needs to be at?
Regards Andy.

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