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Rotax 912 Cooling issue / Zodiac CH 601 HDS

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thilo.kind(at)gmx.net
Guest

Posted: Thu Jun 07, 2007 1:30 pm Post subject: Rotax 912 Cooling issue / Zodiac CH 601 HDS

Hi folks,



got an issue with the cooling system of my Rotax 912 UL: in the past, CHT 

temps always were around 100 F and very stable. Water reached 215F during 

climb out and dropped back to 140 F during cruise. Also, cooling fluid 

always expanded into the overflow tank.

During the last annual I replaced some of the cooling hoses and also 

replaced the cooling fluid (50% / 50 %). I'm not sure, what the percentage 

was before the replacement.



Now, water runs around 215 F during climb out and 205 F during cruise. CHT's 

are very erratic from 100F to 150 F with an increasing tendency during the 

flight. Oil was normal as always around 195 F. Immediately after landing, I 

checked the engine and everything appeared normal, except there was not more 

than the minimum of cooling fluid in the overflow tank. I'm a bit of a loss 

and would appreciate your input. My thought right now is, that the glycol 

percentage is now higher than before, resulting in less heat transport and 

thus  higher cooling fluid temps. At the same time, the boiling point is 

higher, thus less presuure in the system and now overflow in the overflow 

tank. The erratic CHT temps could be caused by air still trapped in the 

system.



Any comments are highly appreciated.



Thanks



Thilo

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daberti(at)sbcglobal.net
Guest

Posted: Thu Jun 07, 2007 5:06 pm Post subject: Rotax 912 Cooling issue / Zodiac CH 601 HDS

You have air in the system, more than likely in the underbelly radiator.  I

put a valve in the aft end of the radiator (petcock type) and the air bleeds

out very easy now.



Dave 912uls HD



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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Jun 07, 2007 8:06 pm Post subject: Re: Rotax 912 Cooling issue / Zodiac CH 601 HDS

HI Thilo,



Couple of things here. Let's look at the CHT max temps. They are 266F. You are running very cool and it would be better running a little hotter (above 200F). You may be right about the different coolant ratio, but with the temps you are running don't worry about it. The CHT temps can change 50F from mid-range throttle at around 4400-4750 rpm and will cool off when at 5000 rpm. Mid-range (4400-4750 rpm) in a 912uls  runs hotter CHT's than at 5000rpm. It was set up that way. If there is a small amount of air in the system then it will work its way out and that's an "if there is air". Rotax would like to see the oil temps around 200F-220F so you are a little cool with the oil which is ok. Optimal running rpm is 4800-5200rpm. My expansion tank never gets overflow. You may need a new pressure cap or you didn't have enough anti-freeze in the water? Your running so cool you may want to consider running Evans NPG+ coolant.



Depending on my rpm and the OAT then my GHT will differ 20-50F.

Your old temps were too cool.

Give your engine a few hours and see if things settle down.

You should not have anything to worry about with your temps now.

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JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Jun 21, 2007 9:41 pm Post subject: Re: Rotax 912 Cooling issue / Zodiac CH 601 HDS

 	  thilo.kind(at)gmx.net wrote: 	
		  Hi folks,



got an issue with the cooling system of my Rotax 912 UL: in the past, CHT 

temps always were around 100 F and very stable. ......



CHT's 

are very erratic from 100F to 150 F with an increasing tendency during the 

flight. 



Thilo 	




CHT's running 100 degrees F ????   That does not make any sense at all.  That is very close to the reading you would get with a completely cold engine.   Something wrong in your readings, or in your reporting of temperatures.  A CHT 100 degrees for a running engine is impossible.



Mike

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Kolb MK-III Xtra, 912-S

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