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This 912 ULS with 1320hrs in a Tecnam SLSA has developed a coolant leakage problem.  After pressure testing the system and replacing several aging leaky hoses including new clamps and replacing the expansion tank cap with a new cap and checking that the overflow bottle line and bottle were clear and making sure the overflow bottle cap vent was open the engine still needs to have coolant added after every flight.  No coolant leaks on the hanger floor, but it seems coolant is leaking in flight with evidence of coolant on the firewall and blowing out the cowling.  Before each flight, the expansion tank is checked to make sure it is full and the overflow bottle is serviced to halfway between the min and max marks.  After a short flight with the engine still warm, before it has a chance to cool and suck the coolant back into the expansion tank the overflow bottle is found empty.  Coolant is found around the overflow bottle cap and on the firewall.  Could there be a cylinder head crack leaking combustion pressure into the cooling system?  How about the coolant system pump?  From my time working with automobiles I know, there is a testing tool for checking if combustion is leaking into the cooling system.  But if such a test is performed to find which cylinder is bad the spark plugs have to be shorted one cylinder at a time.  If you disconnect and or short out a set of plugs on one cylinder so it is dead will that damage the CDI ignition system?  


Jeffrey Fritts, USAF (ret.)

www.flywwlsa.com

"In aircraft maintenance, good enough is not good enough."

  • Re: Coolant Blow Out...

    by » 3 months ago


    Jeffrey have a really good look at the expansion tank (the one with all of the hoses connected to it) where the 2 rubber seals of the pressure cap sit. I have seen corrosion in this area causing similar leaks. I do hope that this area is not compromised as the cost of a new tank is more outrageous than the cap.

     

    Regards.......Chook.


    Thank you said by: Jeffrey Fritts

  • Re: Coolant Blow Out...

    by » 3 months ago


    Cap should be used 1.2 bar on radiator.

    Which type of coolant you are using?

    Evans or Dec coolant?

     


    Thank you said by: Jeffrey Fritts

  • Re: Coolant Blow Out...

    by » 3 months ago


    I have found sharp edges on some of the hose nipples coming off the heads and sometimes the edges cut thru the inner lining off the hose and then coolant wicks/leaks out the fiber mess that is molded in the hose to strengthen it. 


    Thank you said by: Jeffrey Fritts

  • Re: Coolant Blow Out...

    by » 3 months ago


    Check the bottom of the expansion tank for wear, the rubber plate may have slipped out of position and allowed the tank to contact the engine case


    Thank you said by: Jeffrey Fritts

  • Re: Coolant Blow Out...

    by » 3 months ago


    Wayne Fowler, you have won the remote troubleshooting award of the month.  While observing the level of the coolant in the overflow bottle it was discovered that when starting a cold engine the level would rise as the engine warmed to operating temperature.  Now we expect some expansion but this level rose and didn't stop.  The expansion tank had a new cap and to eliminate the possibility the cap was bad it was switched with a known good cap from another plane.  Same test and the same results.  Applying a Scotch Brite pad to the inside of the expansion tank neck and removing the corrosion and rough spots from the bottom sealing surface allowed the cap to actually seal and hold pressure.  Problem solved.  

    Thank you again to all the respondents on Rotax-Owner.com.  This Web site is a valuable resource.  


    Jeffrey Fritts, USAF (ret.)

    www.flywwlsa.com

    "In aircraft maintenance, good enough is not good enough."



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