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Another Angle on Oil Temps?


207WF

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Oz,

Fd could have made cleaning easier if the didn't weld the oil and water cooler together. I have to wonder what goes thru the minds of the guys who design our planes.

Makes me want to scream. I am doing a couple of trials this weekend and will post results.

Maybe we can figure this out for all those that suffer from the dreaded oil temp phenomena.

Chris

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Interesting angle on the angle, guys. How do you know the direction of the airflow in climb versus cruise in order to think about this? My radiator is tilted inward at the bottom edge, relative to the inlet hole in the front of the cowl. That is, the top edge of the radiator is closer to the cowl than is the bottom. My oil temp pattern is the oppposite of Roger's: hot in the climb then cooling in cruise. So, which direction do you think I would wish to change the tilt to experiment? WF

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Bring the bottom edge forward, but the rear radiator bracket may not have enough play and pr the hoses may be too short for some. I flew this morning with 2 other CT's they were around 220F-230F and I was 190F on climb out with an OAT of 88F. When I leveled off it went to 210F and they were at 220 F. I have also re-routed my oil return hose off the bottom of the engine to allow for sweep and less sharp bends in the hose. This may help as I think the original is too sharp a radius bend.

The prop pitch can have a large dramatic effect on the oil temp. I get 5600 WOT flat and level at 4000'. If you get under 5500 rpm WOT flat and level then that is loading the engine and causing more heat. Using a K&N air filter will help.Too many over oil the K&N making it harder to pass air which will raise temps. My point is each one of these adds its own little contribution which adds up.

 

 

You would need longer oil hose and fire sleeve. Pull the muffler down. Turn the bottom large banjo bolt from the left side to the right. Then run the new oil line over, the sweep it up and back into the oil tank. Now the hose has a nice easy "S" bend. The hose stays in a nice round configuration. It's a little longer, but so what. I tried the original way and did it at first with no fire sleeve so I could see the hose bend. I believe for some the radius is reduced from the bend which slows the oil which will raise the oil temps. Is everyone's like this? Probably not. It may not even be a position relative to the air, but some have smaller gaps around the edges so the air flow does a better job?

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I suspect that the angle means little. I can fly at 3 different flap settings and a variety of pitch attitudes and still no joy. The only thing that gets me into the green is climbing above 72 degrees F. Once I cross that altitude I am fine below it I'm in the yellow even in level cruise.

 

When you say pitch attitude do you know what the angle of the radiator is to the relative wind? What is the radiator angle when straight and level?

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Roger:

 

I don't get it. Transitioning from climb to cruise should be "like" rotating the radiator back on the bottom, not forward on the bottom, from the perspective of the air flow angle, right? It seems that I should do the opposite of what you say since I am cooler in cruise. WF

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I'm not convinced it is just an angle to air flow, but more of a gap around the perimeter of the cooler. Like I said I haven't spent any time with any research on this. It's just been looking and experimenting with flight angles . I'm not sure why I'm so much cooler in climb. I'm out of town for two weeks so it will be a while before I play around to look at this.

I know being cooler in climb is usually just opposite of what usually happens.

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Starting do work on flow thru the radiator and was wondering if anyone had ever done a differential measurement of the cooler setup using a magnehelic gauge setup?

Cht's are in the green which is leading me to believe that the ram air ithru the upper cowl is flowing thru the cowl at the correct rate, leaving flow thru the lower section as a possible cause. Only way to measure the flow thru the color is differential pressure at the front and rear of the cooler and then a pressure measurement at the lower edge of the firewall. Any other suggestions or thoughts are always welcome.

I am trying post a couple of sketches For illustrative purposes.

Chris

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You can measure if you want, but it's easy enough to just move the radiator a little and go fly and see what readings you get. Square the radiator in the opening and try to move the bottom of the radiator a little more forward towards the edge of the cowl's lower edge of the opening.

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Roger,

I am trying to use more of a data driven approach to solve the problem and maybe help all the others that struggle with high oil temps at various times. I will be heading up to osh and talking to the guys at fd and rotax.

Interesting note is that this problem plagues the rv12 also. Needlesa to say i will be talking to the guys at van's also

Chris

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One of the things I'm going to do at OSH is take my tape measure and camera and carefully note the size and relative location of the air inlet on the CTLS. On the CTSW, the oil cooler is no where near centered on the air inlet. I don't know if that's an issue, but I will ask some questions of FD on it.

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The radiator should be aligned with the opening and yes it does make a difference. FD has done the air flow test and I would not mess with air flow under the cowl. Move the radiator if need be, it will make a difference. You usually only need 10F - 20F and that is much. Playing with air flow under the cowl doesn't alway move air where you think it should go.

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The plan is to measure the pressure differential across the radiator and at the area at the firewall 2 inches above the opening. Once i collect that data with the components in the present state i will move the radiator up into the opening and perform the same tests. I will post those results upon completion.

 

Anyone care to guess what the pressure differential in inches of h2o should be based on our sandwich design?

What will it measure in the present

How about at the firewall?

Chris

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Mocfly:

 

Where did you get those thumbnails? Very interesting. I wonder how to check for the case described there of air leaking past the cylinders? I like your data driven approach and will be listening with great interest for your results. If you can help us fix this thing, it will be a great contribution. My CT will be like a whole 'nother airplane in the summer! WF

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  • 2 weeks later...

Experimenting with the angle of the radiator, my plane had it bolted at a 40 degree angle from the floor while another plane - whose oil temps run even higher than mine -- had about 30 degrees. We were able to get the bottom of my radiator closer to the hole as Roger suggests. It now measures a 50 degree angle from the ground and the bottom of the radiator is close enough to the cowl that the rubber baffle on the bottom of the radiator now touches the cowl and curls slightly upward, sealing the gap much better it seems. In three test flights under near identical condtions I found that this change made no measureable difference in cruising oil temps or in CHTs in any configuration, but I did not need to pull the power back quite as much when the oil hit 240 (I won't let it go above 250, just power back before it gets there), and it seemed to cool down a little faster after I powered back. This is climbing at flaps 0. No magic bullet, but a little better I think. WF

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Wayne,

 

Another thing that can cause these high oil temps is the oil line off the bottom of the engine back into the oil reservoir. FD has a fairly tight bend and if the heat allows for the hose to get a little too soft (which may happen with age) then it gets a bad bend that reduces flow and raises temps. I have changed mine and put a much gentler sweep in my hose and now it's also a little longer. I pulled the radiator, angled the crankcase oil fitting on the bottom towards the battery verses towards the oil tank. This allowed a much nicer "S" turn in the hose without any restriction in flow. 4-5 years back this is a check that FD wanted done to look for a reduction in oil flow back to the tank which slows the oil down through out the engine allowing it to get hotter. I also have header wrap on my exhaust tubes to help cut down under the cowl temps. Unloading the prop pitch to get 5600 rpm WOT will help for those who have not done so, plus an increase in performance over those that 5400 rpm or less WOT.

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  • 1 month later...

I saw this thing in the EAA mag called an oil chiller. It looked like a bunch of metal fins stuck around the outside of an oil filter. That would not work on a CT, but I wonder if a similar approach might help if applied to the bottom of our oil tank? Do you think cooling the oil that is in the tank would make much of a difference? WF

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If there was a baffle above the oil cooler and between the cowling, as there is on the bottom edge, might this help in reducing the oil temps, or is that upper air flow required for other engine cooling?

 

Any opinions or has anyone tried this?

 

I have an experimental CT so this kind of change would work.

 

Roger Kuhn

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