582 radiator cap PSI

[thebriman 69]

What are y'all using as far as cap pressure.  I have a Motorad T-13, (.9 kPa).  It leaks and needs to be replaced? Are you guys running the 13 pound caps or higher?

 

 

Brian

[High Country 69]

I currently have the 13lb on my project and that seems to be what was most commonly sent out... however I just came across this http://www.rotax-owner.com/rotax-blog/item/13-on-the-fence-about-coolant today while looking for what coolant I need and it states in the 2nd paragraph that if you're running a 50/50 mix you should be using an 18lb cap.

 

-Robert-

 

Edit: just found this to http://airplanepilot.sportaviationcenter.com/airplane-lsa-pilot/maintenance-inspections/rotax-airplane-operations/rotax-cooling/

 

Water Based System

• Maximum coolant exit temperature for 0.9 bar/13 PSI pressure cap is 239 F
• Maximum coolant exit temperature for 1.2 bar/17.5 PSI pressure cap is 248 F
• Recommend change to higher pressure cap if coolant temperatures are high
• Use distilled water, not tap water, to eliminate corrosion from tap water impurities
• DEX-COOL coolant (marked on manufacturers bottle) is common type to use. DEX-COOL American version is orange.
• Use only coolants and mixture ratios recommended by ROTAX at www.rotax-aircraft-engines.com

Edited 22 Jun 2014 by High Country

[thebriman 69]

Im in the same boat.  My 13 worked fine but leaks now, and I saw that they say I need an 18.  Im thinking Ill get a 13 again because it worked for 20 years so why mess with success.  

[EDMO 1078]

Question:   Since the sea-level air pressure on everything is 14.7 psi, then is a 13 psi cap really a 27.7 pressure, because 13 psi could not overcome outside air pressure?

EDMO

[thebriman 69]

Correct,  13 PSIG not PSIA.

[Av8r_Sed 82]

The OP was referring to a 582 installation.  The referenced links I believe apply to a 912.  The Rotax installation manual for the 582 calls out the 13 psi(g) pressure cap (section 11.3.4).  Also, in the operating manual, the max operating water temperature is stated to be 175°F and minimum for takeoff is 150°F.

[thebriman 69]

Thanks Sed!

[marksires 484]

Question:   Since the sea-level air pressure on everything is 14.7 psi, then is a 13 psi cap really a 27.7 pressure, because 13 psi could not overcome outside air pressure?

EDMO

Nope. The air pressure is constant on both sides of the cap.  If you want to be technical, it is a 13psi differential cap.

 

Mark

[EDMO 1078]

I'm not getting any deeper in this stuff - This has been an ageless debate - Just threw it out to see what answers came back.

     My Physics Professor thought that he was one of the few in the world who knew the correct answer - and I forget what that was - must have been in a vacuum at the time?

 We then went into the leverage or force to move the earth - forgot to where!  

EDMO

[marksires 484]

Not much to debate.  If you take a 13psi cap into outer space (vacuum), put it on the radiator (which also has vacuum in it in space), then start pumping air into the radiator, when the radiator pressure exceeds 13psi, the cap will pop.  Or, if you put the cap on the radiator at sea level (14.7 psi) and start taking it up in the atmosphere, when the ambient pressure drops below 1.7psi, the cap will pop.  When the pressure on the inside of the radiator is 13psi more than the pressure on the outside of the radiator, the cap pops.  It doesn't care why the difference developed, just that it is.

 

Even more fun, take the radiator to the bottom of the deepest ocean (about 25,000 feet or a rough 12,250 psi pressure), then put the cap on.  As you raise it back to sea level, what happens?  Absolutely nothing.  Water is uncompressible, and the radiator would have been full of water at 25,000 feet.  Since the water wasn't compressed, no pressure difference occurs.  Of course, if you put the cap on an empty radiator at sea level, and then sank it to the bottom, you'd bring back up a small, flat radiator that wouldn't hold much water.  

Mark

[EDMO 1078]

Mark,

      Were you my Physics Professor?  I forgot his name, along with all the "good stuff" he thought he taught us! 

EdMO

[ChrisBolkan 130]

I ran a 13 PSI cap, distilled water and 10% DexCool in the summer. Found that temps ran considerably cooler running less coolant. Back to 50/50 in the winter.

 

PSIA  - Professional Ski Instructors of America.

 

Chris

[marksires 484]

Mark,

      Were you my Physics Professor?  I forgot his name, along with all the "good stuff" he thought he taught us! 

EdMO

Wait, were you the one I had to keep sitting in the corner with the isosceles cone on your head???  

[EDMO 1078]

Glad you remembered me! 

EDMO