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Oil Temperature runs high on climb out . . .


ibjet

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Yes, I had not seen that second picture. That is "the fleet" from what I read (a very small number that were not destroyed). The one that I took the picture of at Kingman was there for paint touch up. I'm thinking maybe he is a Beechcraft executive???

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  • 2 months later...

I just changed oil for the first time and in the process took a close look at my radiator stack. I noticed quite a bit of oil and some debris in the cooling fins. I was thinking I might need to remove the cooler stack, but my AI buddy recommended using 505 solvent and I ordered a wand spray gun with a venturi pick up tube so I will clean it up that way. The spray gun wand has an angled tip so I think I can reach behind the radiator and clean with a reverse air flow (might end up unbolting the radiator so I can angle it better/get more room). 

Good thing to check for when you are looking at the engine or even pre-flighting. 

One more tid bit of info: I did not attempt to fill or partially fill the new filter with oil. But, when I started up the engine, the oil pressure came up almost instantly. Conclusion - no need to pre-fill the new filter (it would be a huge mess anyway). 

Happy skies to you . . .

 

 

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You can't fill the oil filter like they used to due to a change in the filter design.

You should follow the procedure of rotating the crankshaft 20 turns though (50 rotations of the prop if you have a ULS), which will prefill the filter and purge air from the system. Rotax's tappets are sensitive to air, and can in rare cases, lock up briefly and cause something to bend. Then start up.

Anyways, if you get a little warm on takeoff, just shallow your climb some so you get some forward airspeed. Pretty much every airplane out there can't take really hot weather in a hard climb and the extra speed will increase airflow in the engine compartment.

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Thanks, I think I burped it before I started it, but not sure. I remember wondering if you couldn't pump oil into the filter that way.

Thanks!!!

I climb to 1000 AGL, then I shallow out and throttle back slightly. But, with a clean radiator I'm hoping to see it much less sensitive. It will be hard to tell now because the weather has really cooled.

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I know that wrapping the exhaust pipes can keep the under-cowl temps a bit lower.  Does anybody know if it actually makes the engine run cooler?  I'm wondering if keeping the radiated heat from the pipes inside the pipes might help keep the oil cooler, lines, and cylinders from getting heat soaked...?  I'm about to wrap my pipes, just wondering if I can expect any measurable decrease in oil and/or cylinder temps. 

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38 minutes ago, Mike Koerner said:

I would expect an increase in oil temperature...

What would be the mechanism for that?  The heat is staying in the pipes, and might even create better exhaust scavenging and thus better exhaust velocity.  Not sure why the oil temp would go up, but I admit I'm no expert! 

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The wrap inhibits convective and radiant heat transfer from the metal outer surface of the pipes to the surrounding air and the surrounding structure respectively. Those are the results you wanted. But as a result of reduced heat transfer from the pipes, the pipes themselves get hotter. that means more heat is conducted back through the mounting flange to the head. That is a result you don't want.

So, the question is, which effect wins. The heat transfer coefficients for convection and radiation are much lower than that for conduction... favoring unwrapped. However, delta-T plays an equal role. The temperature difference between the pipes and the surrounding structures is much lower with wrap than without, while the temperature difference between the pipe mounting flanges and the heads will only be slightly greater with the wrap... favoring wrapped.

There is insufficient data for a definitive answer, and testing would be both easier and more accurate than a thorough analysis. However, I am swayed, slightly, toward unwrapped pipes by the fact that there is, I believe, significant air flow through the cowling. This forced convection will essentially negate the convective heat transfer from the pipes to the surrounding structures, leaving only the radiant effects to counter conduction.

As I said, I would expect (maybe guess would be a better word) that the difference is probably not a significant, or even measurable.

Mike Koerner

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56 minutes ago, Mike Koerner said:

The wrap inhibits convective and radiant heat transfer from the metal outer surface of the pipes to the surrounding air and the surrounding structure respectively. Those are the results you wanted. But as a result of reduced heat transfer from the pipes, the pipes themselves get hotter. that means more heat is conducted back through the mounting flange to the head. That is a result you don't want.

So, the question is, which effect wins. The heat transfer coefficients for convection and radiation are much lower than that for conduction... favoring unwrapped. However, delta-T plays an equal role. The temperature difference between the pipes and the surrounding structures is much lower with wrap than without, while the temperature difference between the pipe mounting flanges and the heads will only be slightly greater with the wrap... favoring wrapped.

There is insufficient data for a definitive answer, and testing would be both easier and more accurate than a thorough analysis. However, I am swayed, slightly, toward unwrapped pipes by the fact that there is, I believe, significant air flow through the cowling. This forced convection will essentially negate the convective heat transfer from the pipes to the surrounding structures, leaving only the radiant effects to counter conduction.

As I said, I would expect (maybe guess would be a better word) that the difference is probably not a significant, or even measurable.

Mike Koerner

Great explanation, thanks Mike!  

I agree that conduction is more efficient than convection, but...

The conduction surface area, essentially the pipe flange at the cylinder head, is far less than that of convection, which is the entire area of the pipe.  I'm not saying that convection wins, but just that the difference between the two must be high for conduction to win.  Further, when the engine is running, the exhaust pulses work to carry the component of additional heat transferred to the gasses in the pipe away from the cylinder head.

Again, I don't know what the net result will be (probably not measurable, as you said), but it's interesting to speculate!  Physics is fun! 

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The coolant will compensate for the increase in pipe temperature, the exhaust is one of the areas that gets the most coolant. It will have next to no effect on the oil in the grand scheme of things.

The rings help conduct heat from the piston to the cylinder, and oil picks up the heat from under the piston heads and a bit from the cylinder walls. That's what heats the oil.

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ibjet, please let us know what your cyl. head and oil temps where before and what they are after cleaning the radiator exteriors.  Since these temps depend so much on ambient temps and mode of operation if you can give same conditions before and after this would be helpful.  I ask about his since I'm wondering what the "typical" CTSW temps are with a good number of owners.  Since CTLS has thermostats, I am asking about CTSW only.  I normally cruise my CTSW around 5300 to 5400 rpm.  A typical summer day for me is mid 85F.  At 3,000 AGL, my ambients are around 70 to 75F.  A good comparison can be made if others might know their temps at this condition.  Andy, you have a CTSW and live in a warm climate.  Can you provide your temps?  Others? 

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Hey Dick, I usually see 210F to 230F in cruise at 3000+ in summer at 5200-5400rpm.  I often hit 240-245F in climb, I don’t let it go above 245 if I can help it.  Those numbers are in temps of 95+ at ground level (800-1000ft MSL).

when the temps go down a bit my temps are much cooler.  I see 180F in cruise when temps are in the 70s at ground level.

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Andy, thanks for the temps.  My temps are similar.  I might run a little higher than 180 when temps are high 70's/low 80's ground level. On a low to mid 90 day, which we've had the last few days here, I'll bump 240 if I do a long climb from low to higher altitudes @ WOT.   Next rubber change, I need to check for kinking of the oil hose that does a 180 from the oil pump back to the radiator and also need to do Roger Lee's recommended direct routing for the oil return off the engine sump to oil reservoir.  These two items will adversely affect oil temps if not attended to.

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Another data point.  Took off today with ground temps ~90F, climb out from 900ft to 3000ft (75F OAT)  got the oil temp to about 230F.  Leveled off at 5300rpm and oil temp stayed about 220F for the entire 70nm trip, which I consider my "perfect" temp...hot enough to boil off water but not hot enough to worry about.  CHT 190-200F the entire time.

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