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Oil temps back to new after all these years


Ed Cesnalis

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I flew to Tracy today to have Jeremy mount my goose neck tablet mount.  He also replaced the rubber seals around my coolers because they were deteriorating.

 

It was a warm day and on my way in my oil temp went from 230 to 235 in the yellow asdescended from 11,000' to 2,000.  

 

On my way home the initial climb is to 9,500 from sea level and I expected to see 265* (redline) the question was 'at what altitude?'  

 

At 6,000' climbing at 500fpm I hit 250* and by 8,000' I was back in the green at 230*.  The cruise home was at 220* which is 10* lower than normal and even the cylinder head coolant was 10 to 15* cooler.  These cruise temps are better than new and the climb temps are at least pretty close.  We were looking in all the wrong places.

 

I guess my deteriorating rubber flaps were a big deal even though they looked pretty good until recently.  Both temps are down so I think there must be a lot less airflow bypassing the coolers.

 

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Trip home was in the afternoon and I had to cross the Sierra Nevada that was now full of clouds.  The peaks were obscured, cloud base was at 10,000  and I couldn't see the  passes.  The lowest of the high passes was 50 miles in front of me and I was squeezed by the low clouds and in the bumps just below them but I knew that I could squeeze through if the ceiling was above 9,600 and I knew the east side higher pressure would add to the clearance once I set a local altimeter so I pressed on.

 

Clouds were low enough were I had to rely on GPS to know where I was so I utilized some low route way points that I had recently created when playing with Garmin Pilot.  My instincts were wrong so my late night way points saved me some grief and got me home easy peasy like on a marginal day.

 

 

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You got hotter descending?  That seems not good.   You were not flying IMC of course....that would be wrong.

 

My throttle was wide open and the ambient air temps in the central valley were hot down low.  If I descended by simply pulling power and it got hotter that would really be not good.

 

On the way home I stayed VFR easy enough.  

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Hi ED,

 

 Your max is only 248F per Rotax, not 265F. Getting that high a temp may cause a vapor pocket in the heads and they will not be cooled and will warp or have the metal soften. Up to 240F in climb during the summer would be more in the normal range. I would definitely stop at 250F. Mine is usually 230F and on a really hot day and long climb 235F. 

220F in the summer for cruise can be very normal. That said at your high altitudes it should be lower, but you run at 5500 rpm WOT and that builds more heat. More fuel burn more BTU's generated and air flow doesn't increase from 5200 to 5500 to make up the difference. If you throttle back to 5200 rpm in cruise those temps may go down. The temp could have gone up momentarily due to the fuel flow change and then it should have gone back down.

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Sorry if I got the number wrong, with my eyes I focus on the green that I know tops at 230 and its been a while since I've seen redline but somehow I had in my head the number was 265.  So I topped out half way in the yellow that must be what more like 240?  My misreading aside my oil temps are lower than new and I'm really happy.

 

Now that I'm cruising at 220 why would I want to throttle back?  I'm severely restricted powerwise by the high cruise altitudes and I'm not restrict it even farther with my throttle.

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Hi ED,

 

 Your max is only 248F per Rotax, not 265F. Getting that high a temp may cause a vapor pocket in the heads and they will not be cooled and will warp or have the metal soften. Up to 240F in climb during the summer would be more in the normal range. I would definitely stop at 250F. Mine is usually 230F and on a really hot day and long climb 235F. 

220F in the summer for cruise can be very normal. That said at your high altitudes it should be lower, but you run at 5500 rpm WOT and that builds more heat. More fuel burn more BTU's generated and air flow doesn't increase from 5200 to 5500 to make up the difference. If you throttle back to 5200 rpm in cruise those temps may go down. The temp could have gone up momentarily due to the fuel flow change and then it should have gone back down.

 

 

Seems my max per Rotax is 266. Revision 1 states 285 degF. Revision 2 of the Rotax Operators Manual states 266 degF.

 

248 is a Dynon setting so it doesn't apply to me I don't have Dynon.

 

Seriously sounds like you've changed, long ago my temps were of no real concern because there is safety margin if you use 266 and full syn.  Now its may cause ... ?

 

 

For years 265 was unavoidable on summer climbs and now that I can beat that your moving my redline?  :no-1012:

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You're outdated . Go get the latest Operators manual. Edition 3, Rev 2. Feb. 2015.

Go to either Rotax-Owner .com or Fly Rotax website to get all the current manuals. Then go check all the SB's that apply to you.

You are restricted to 248F when using 50/50 coolant because of possible vapor formation in the heads and loss of cooling. This has been like this for the years on the temp even before the last manual revision. 248F is on multiple pages and SB's

 

If this happens get a second mortgage out on the house to test and replace heads.

 

I haven't changed. I never knew you were that high. When you say overheat that means 250F to me. 265F shouldn't even be on the table.

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Roger, I have seen you state before that oil temps of 250°F or below are not a cause for concern.  Has that changed?  I was seeing 240°F in a climb last weekend, and that's not unusual for summer in Georgia.  Is that too hot?  We've been having a mini-heatwave here, with ground OATs in the 94-98°F range.

 

The yellow arc on my oil temp gauge reads from 230°F to 250°F, with a red line at 266°F.  It sounds like those ranges are now too permissive...?

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I would not want to be above 250°F, but I do see 240°F in the summer with some regularity.  Not sure if I have ever been over that, even in 95°F or higher ground temps.

 

What happens when the coolant vaporizes, a loss of cooling efficiency and high pressure in the cooling system?

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if your coolant vaporizes you have no cooling in the heads. They over heat and soften which many times causes warping and then you replace the heads. 240F is no big deal in climb, but should come down in cruise.

 

It does.  Saturday once I got to cooler air at 4500ft oil temp came down to about 216-220F.

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Stagnant temperature inversions are not uncommon in the Sacramento Valley.  I've had the outside temp be as much as 10 degrees hotter at 4,000 feet than at ground level.

 

All valleys get inversions usually during winter.  Usually burns off by noon.  Comes when air is stable, high pressure, cold ground.  Sometimes happens on coasts due to cold water mass.  Ground fog, advection fog, opaque air and low air quality are all symptoms.  Can happen at any ground level, high valleys or low.

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You're outdated . Go get the latest Operators manual. Edition 3, Rev 2. Feb. 2015.

Go to either Rotax-Owner .com or Fly Rotax website to get all the current manuals. Then go check all the SB's that apply to you.

You are restricted to 248F when using 50/50 coolant because of possible vapor formation in the heads and loss of cooling. This has been like this for the years on the temp even before the last manual revision. 248F is on multiple pages and SB's

 

If this happens get a second mortgage out on the house to test and replace heads.

 

I haven't changed. I never knew you were that high. When you say overheat that means 250F to me. 265F shouldn't even be on the table.

 

I have a current condition inspection with all service bulletins complied with.  My oil temp gauge is still red-lined at 266*F.  What got missed?

 

HI Andy,

No issue with 250F, but that's max. It's only 2 degrees above 248F. Rotax has not wanted anyone near 265F for years because it is too close to the 270-275F for 50/50 coolant to vaporize.

 

I only have a little time since my temps dropped.  Prior to the recent drop there was a pretty big spread between my oil temp and my dexcool temp.  When hot there has been a 20* spread, when I approached 266 my dexcool was ~240*.  Seems to me that if the 50/50 coolant is the problem the max should be on the 50/50 not the oil.

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No I'm talking oil temp. The max is 248F. Your CHT reads metal temp not coolant. A 20F spread between CHT and oil temp is normal. Worry about the oil temp first. That will reach max first. If you have a new enough Rotax engine or head the probe does extend into the coolant. 266F is to high. It is 248F max. 50/50 isn't the problem and Evans is 20-30F worse. It all comes down to air flow, radiator placement and size and coolant flow.

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Roger,

 

Are you saying that my red-line changed via SB but I'm not in compliance or that the advice from Rotax changed and my red-line is unchanged?

 

I have been right there at 266* doing initial climbs a number of times in the past.  What damage did I do?

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No I'm talking oil temp. The max is 248F. Your CHT reads metal temp not coolant. A 20F spread between CHT and oil temp is normal. Worry about the oil temp first. That will reach max first. If you have a new enough Rotax engine or head the probe does extend into the coolant. 266F is to high. It is 248F max. 50/50 isn't the problem and Evans is 20-30F worse. It all comes down to air flow, radiator placement and size and coolant flow.

 

Roger, max oil temp is 285F, max coolant temp is 248F, and max CHT is 300F.

 

Doc1.docx

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Hi Tom,

 

Those are UL temps and not ULS. Remember the manuals are written for 3 basic engines. ULS max CHT head temp is 275 and coolant is 248. Max oil is 266, but with 50/50 it should be held to 248.

 

With 50/50, why should oil be limited to 248 if the intent is to avoid the coolant max? Max coolant is already 248, why isn't that sufficient? Why create a an 18 degree reduction in max oil for artificial reasons especially when that reduction will make a lot of operations in the western US now not doable?

 

A number of ULS owners have to go to their 266 red-lines just to sustain their initial climbs for more than 2-3 thousand feet in the summer in the West where 10,000 is typically needed. Artificially limiting these aircraft and by extension their owners for such a bureaucratic reason isn't going to happen in the real world.

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Hi Ed,

 

Believe it or not few have to see 266 in their climb. Seeing those temps all the time in climb may be inviting trouble you don't want. Most only see 230-240 during the warm months. I would never run my engine over 250 and if I got that high I would want to know why. There are a few at 245-250 (a few CT's), but those are usually in different planes with different cooling set ups.

I can climb to 10K and not see over 230-235. Now you need to ask why is yours different from mine.

You can use a Dremel and open the radiator opening more for better air flow.I did this to mine.Part of the radiator on some CT's are partially covered.

 

p.s.

If all you can get at WOT at your altitude is 5500 then flatten the pitch more and unload the work on the engine. This may help bring the temps down a little more.

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