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I'm experiencing high CHTs.  As soon as I start the engine the CHTs just keep rising and reach 100 - 110 deg C before the oil reaches 50 C.  On two occasions I've had coolant spray out the overflow bottle onto the firewall.  With the arrival of the cooler weather the problem has been exacerbated because of the longer ground idling time waiting for the oil temp to come up.  Today after a full engine run up I had CHTs at 123 C and 128 C with oil at 57 C.  I've changed the coolant (using 50:50 Radicool:distilled water) and bled the coolant system via the bolt with copper washer just below the water pump.  I've cheked all the hoses for tight turns and today I swapped my radiator cap for an unused one but it made no difference.  When I did a full engine run up today the coolant expanded into the Rotax overflow bottle and it made so much noise I could hear the gurgling while the engine was still running.

 

I'm getting 5200 rpm static.  

Only one EGT gauge works and it reads 505 C.

The engine is on a Rans S-19 with only about 13 hours flight time. Others with the same plane and engine aren't experiencing airflow issues so I don't think that's a problem here.

 

Last week I had a former Rotax specialist look over the engine and we found that the carb heat was actuated all the time because the butterfly mechanism on the air box wasn't opening and closing correctly. That has now been rectified but it hasn't helped with the high CHTs.  

 

Next week I will flush the radiator and check the vanes on the water pump's impeller.  Are there any other suggestions as to what I might try ?? 

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  • Re: High CHTs

    by » one month ago


    Does your engine have a coolant thermostat? Any work done on the plane recently or did this just happen out of the blue? 

    With only 13 hours of time it is possible you have some debri in the system. You can switch the oil temp wire with the CHT wire. Then to coolant will read on the oil indicator on your instrument. The sensors are the same and that can rule in or out the sensor. Flushing the coolant radiator certainly won't hurt. Flush it backwards.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: Chris O'Donnell

  • Re: High CHTs

    by » one month ago


    I was going to guess that the coolant level was low, but it looks like you have eliminated that possibility.

    Top off the radiator.
    Run it 'til it hits 100°C and then shut it down. The T'stat should have opened by that point.
    Quickly check to see what is Hot and what is NOT.
    For example; if the Heads are hot and the Radiator is cold, there is nothing circulating through the Radiator.
    It might be Hot up to the thermostat but not beyond; indicating a closed 'stat.
    If the Water Pump INTAKE hose is cold; Nothing is circulating.

    And by Cold, I mean you can leave your hand on it for more than One second.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Chris O'Donnell

  • Re: High CHTs

    by » one month ago


    Thanks Roger - No, I don't have a thermostat and I haven't had any major work done recently - just an oil change, a new voltage regulator and a tyre tube, so sort of out of the blue.  I will check for debris. I did have small rubber particles in the rh carby bowl after a couple of hours which was causing rough running.  I blew all my rubber hoses with compressed air but someone has since said it's better to flush them to get rid of foreign particles.  Will try switching those wires. 

     

    Thanks Bill - I haven't installed a thermostat. The only modification I've made to the cooling system is a 25 mm aluminum adapter with 1/8" npt port for a Smith's temp sender - but the Dynon doesn't recognise it so I'll swap the sender out at a later date. 

     

    Regards,

    Chris


  • Re: High CHTs

    by » one month ago


    Sounds like the water isn't passing through the radiator. Have you got one of those IR thermometers? It would be easy to check what is hot and what is not. If you slacken off the upper hose on the rad, does any water come out?

    If you have water in the circuit then I would look at the pump. You can probably remove one of the hoses and push the impeller, if it is loose on the shaft then that would explain your problem. I've looked at the drawings in the heavy maintenance manual and it looks like the shaft is driven by a gear and the impeller is a push fit onto the shaft. I can't see how this would be loose unless the shaft was badly worn but you never know!


    Thank you said by: Chris O'Donnell

  • Re: High CHTs

    by » one month ago


    Thanks Kevin,

     

    I do have one of those IR thermometers so I will put it to use. I plan on checking the water pump and radiator this weekend.

     

    Regards,

    Chris

     


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