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High CHT's on extended climb, but low coolant temp

in 912 / 914 Technical Questions 11 years ago

  • Re: High CHT's on extended climb, but low coolant temp

    by » 10 years ago

    Roger: We tightened all the connections between the CHT gauge and the probes and removed the ground wires, cleaned them up with a wire brush, then replaced them. In our flight test afterward at SZP there was definite improvement, but we are not sure if we are 100% yet. It was about 100 degrees F OAT and after climbing to about 3000 feet the CHT's were 240/235 while the oil was 181 and coolant was 210. Is that CHT about right given those coolant/oil temperatures? I ask as the manufacturer of the gauge (UMA)suspects there might be a problem with the gauge and has offered to check it for us. Thanks!

    Gary Van Meter
      
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  • Re: High CHT's on extended climb, but low coolant temp

    by » 10 years ago

    235F-245F seems fairly high to me for CHT's. It may be a false reading on the gauge. Is this an analog gauge or digital. If it is digital you may need to go into menu and pick a different probe type. In the Dynon EMS you have choices for probe numbers or types and picking the wrong one will give false readings.

    As a rule the oil temp is usually higher than the CHT's by 10F-20F.
    The CHT's should be within a few degrees of the coolant temp. When I climb here in Tucson, AZ with an OAT of 95-100F the oil temps get to around 230F (maybe 235F on a really hot day in a hard climb) and CHT's around 210F. In cruise I usually see on those days at 5100-5200 rpm about 200-208 CHT's and 215-218F oil temps on my plane. Others may be slightly different so these are only examples from my plane. A lot of the temps have to do with air flow and hose routing. Then toss in good carb maint and sync, coolant either 50/50 mix or Evans (hopefully not Evans)and then your local OAT and time of year.

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

      
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  • Re: High CHT's on extended climb, but low coolant temp

    by » 10 years ago

    Roger:
    Thanks again. We have an analog UMA CHT gauge. Our airplane originally had a oil cooler that was too small, giving high oil temps, so we replaced it with a big one, so now we actually need to put in a thermosat or something as it keeps the oil too cool. WE flew yesterday in 80-85 degree weather and it ran a little cooler, but the CHT still gets up into the 230 and above range on climb but water temps generally run about 180 and no more than about 210 on long climbs.

    Do you have a fiberglass shroud over your engine to direct air over the cylinders like the RV 12's?
      
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  • Re: High CHT's on extended climb, but low coolant temp

    by » 10 years ago

    Hi Gary,

    I have a Flight Design CT. It has a tight cowl. My under the cowl temps are only 145F - 149F. I checked it last month. My oil temps on a long hard climb are no more than 230F and my CHT 's are at least 20F - 30F lower than that. When I throttle back and level off the oil temps will settle at around 208F - 215F and the CHT's are around 190F - 200F. OAT is around 85F - 95F.

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

      
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  • Re: High CHT's on extended climb, but low coolant temp

    by » 10 years ago

    Thanks Roger!

    We use 91 octane mogas and try to keep it fresh. Flat and level RPM at 3500 feet is 5800.

    I don't know what position the carbs are in but when I gapped the plugs last I did them on the tight side of the range. So maybe that is a factor. We don't have EGT gauges, but it looks like maybe we should.

    Gary


    Gary, isn't that way high RPM for straight and level?
      
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