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Rotax 914 - at which CHT does the coolant boil?

 
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Roland



Joined: 30 Nov 2009
Posts: 291
Location: EDLE

PostPosted: Thu Apr 26, 2018 2:32 am    Post subject: Rotax 914 - at which CHT does the coolant boil? Reply with quote

Hi,

this year again an extended ground run was necessary at the holding point at the AERO in Friedrichshafen.

Since I had to taxi in OAT of 25°C/77°F first on soft ground with high power and thereafter in a stiff tailwind to the end of the runway to wait in the queue, my CHT climbed to 122°C/251°F. After I positioned myself a bit into the wind and close behind a Mooney to profit from its propwash the CHT settled on 118°C/244°F and decreased fast to normal after take off.

Does anyone know, how the CHT correspond with the actual coolant temperatures? At which CHT is it advisable to shut down the engine?

Regards
Roland
PH-ZTI
Europa XS TG 914


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mojaveclimber



Joined: 06 Mar 2014
Posts: 19

PostPosted: Thu Apr 26, 2018 6:30 pm    Post subject: Rotax 914 - at which CHT does the coolant boil? Reply with quote

Roland:May I recommend Wayne's Waterless Coolant for your R912 application.  There are a number of advantages over traditional water/ethylene/glycol coolant. The higher boiling point reduces internal flash boiling within your engine, your specific concern with over heating on the ramp would be reduced and likely eliminated.  Further advantages, less internal corrosion, improved heat transfer, lower cooling system pressure.  This coolant is popular in  NASCAR, Off Road racing, and has worked well for me in my R582 powered Mk3 and my Ford Ranger Prerunner.  You may want to review these two links. Tailwinds to you
https://www.evanscoolant.com/how-it-works/

https://www.evanscoolant.com/how-it-works/

Jim
On Thu, Apr 26, 2018 at 3:32 AM, Roland <schmidtroland(at)web.de (schmidtroland(at)web.de)> wrote:
Quote:
--> RotaxEngines-List message posted by: "Roland" <schmidtroland(at)web.de (schmidtroland(at)web.de)>

Hi,

this year again an extended ground run was necessary at the holding point at the AERO in Friedrichshafen.

Since I had to taxi in OAT of 25°C/77°F first on soft ground with high power and thereafter in a stiff tailwind to the end of the runway to wait in the queue, my CHT climbed to 122°C/251°F. After I positioned myself a bit into the wind and close behind a Mooney to profit from its propwash the CHT settled on 118°C/244°F and decreased fast to normal after take off.

Does anyone know, how the CHT correspond with the actual coolant temperatures? At which CHT is it advisable to shut down the engine?

Regards
Roland
PH-ZTI
Europa XS TG 914




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Roland



Joined: 30 Nov 2009
Posts: 291
Location: EDLE

PostPosted: Thu Apr 26, 2018 10:48 pm    Post subject: Re: Rotax 914 - at which CHT does the coolant boil? Reply with quote

Thanks, Jim.

But Evans carries a temperature penalty of up to 30°F in a cowled Rotax-installation, thus bringing my engine to the CHT-limit.

During flight the temperatures are ideal. Problems only on ground and in adverse conditions.

Regards
Roland


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Roger Lee



Joined: 10 Jan 2006
Posts: 1459
Location: Tucson, Az.

PostPosted: Fri May 04, 2018 10:38 am    Post subject: Re: Rotax 914 - at which CHT does the coolant boil? Reply with quote

Rotax does not recommend waterless coolant any more after their poor experiences with Evans. What they do recommend is Dex Cool 50/50. Waterless coolants carry that higher 25-30F temperature penalty because water absorbs temp quicker and releases it. Waterless coolant doesn't release heat fast enough.

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Roland



Joined: 30 Nov 2009
Posts: 291
Location: EDLE

PostPosted: Fri May 04, 2018 11:50 am    Post subject: Re: Rotax 914 - at which CHT does the coolant boil? Reply with quote

That's the problem, Roger. There's no advantage for me, if the coolant doesn't boil but I exceed the CHT-limit.

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Roger Lee



Joined: 10 Jan 2006
Posts: 1459
Location: Tucson, Az.

PostPosted: Sat May 05, 2018 5:23 am    Post subject: Re: Rotax 914 - at which CHT does the coolant boil? Reply with quote

Most of the time you can fix the cause of the overheat. Waterless coolant is just putting a band aid on or fixing the result.

Check all hoses to see if one has a reduced radius, move hoses away from exhaust pipes of mufflers or apply more heat shielding, Wrap the exhaust pipes with header wrap cloth, change the air flow through the cowl (possible opening the cooling inlet areas), if you have the smaller radiator see if the larger one will fit, make sure you have the 1.2 bar pressure cap and not the .9 bar cap.


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Roger Lee
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Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
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