Misc. 303 Issues

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  • #83845
    bthomason
    Participant

      This is an exchange between 303 owner and TTCF member John Hodgson and myself about several 303 issues. Any thoughts/comments are appreciated.

      John: Engine heating …. In the air I manage it with fuel flow mostly following the teaching from Ada. For a turbo charged engine full rich or 50 to 70 LOP. Not Top of the Green. But I am not sure what you can do on the ground other than minimize time before take off and delay run up till you are on the runway. I am not sure if you taxi full rich or LOP??? If I am VFR I do not change the mixture control after setting cruise LOP till shut down. You can also run at 1200 rpm to get a bit more airflow
      The problem I am now convinced is a generic design one that all Crusaders summer from not one that is specific to me e.g. baffling. So how do we get more airflow? Pull one of the cowl flap plates in summer??? Or make a spare set of plates with bigger holes (reverse of a strip of duct tape on the oil cooler in winter)? Bigger oil cooler? Get a 337 for 400 series cowl flaps? Add a fan for ground running?

      Bob:I am also having engine oil temp problems during hot day long idles periods. Yesterday I had a 30 minute wait for departure at OSH and the left engine oil temp was steady at about 200 and the oil pressure on my left engine dropped to almost zero. (I’m a little suspious of the oil pressure reading as I have just replaced my AuRacle 2120 with a new box and, in general, the oil pressure is reading lower on that engine than it was before.) Of course, after I took off, oil temps and pressures quickly moved into the normal ranges. My next step will be to check the baffling. I haven’t studied the cowl flap design, but removing the entire structure in the summer might help. Where I live, I leave the cowl flaps open year round. Some of the other options you mention sound pretty complex and expensive.

      John: I wanted to talk about the STC for 27″ and 15 gph. I think that puts the engine into George Brawley’s red box and cooks it. I run 30″ and typically 13.5 to 14 gph and I don’t see why you even need an STC.

      Bob: I do not see a need for the STC either. The STC was developed before GAMI’s research and the renewed understanding of mixture leaning. Knowing what we know now about cylinders pressures and temps, there is a better way to run our engines.

      John: I have had 2 strange experiences in the air …..

      At something like 17,000 feet with high OATs the engines get very hot (CHT and oil). Adjusting mixture and reducing power makes no difference. But a descent by as little as a few thousand reduce the temps to levels you can operate at.

      Bob: I have not had this problem but, then, I fly at low power settings LOP. I run at 24 inches and 2,350 RPM at 50 LOP with fuel flows of 11.1 per side. I also typically fly at little lower, around 15, 000. I’ve had no problems with temperatures in cruise.

      John: IMC at 16,000 I was operating LOP (30″ and ~14gph) picking up some ice, not much but more than a trace and I could see a build up on the cowls around the air intake when I noticed I had lost a few hundred feet and turned 30 degrees left. Lots of brown on the AI. I immediately ran the mixtures to full rich and recovered. It was over in a flash and ATC did not notice. I looked at the JPI file on the ground and I had lost enough fuel flow to cause the engine to loose power. I have no idea why it happened and had the alternate air door checked on the ground but nothing was found to explain it.

      Bob: Hmm, I’m not sure about this one. I’ll run it by Tony. Also, I’ll post this exchange on the online forum and see if any other 303 owners have some input.

      #96420

      For the ground cooling issues have either of you tried a higher rpm and very LOP? The higher RPM would help airflow and oil pumping while the LOP operation would keep the cylinders cool. (LOP on the ground is brutally lean – right at the edge of not firing anymore). I think the natural inclination is to reduce power, but then the prop airflow is lower and perhaps the oil flow is lower (and cooling capacity worse)

      High CHT/oil temp at 17,000 irrespective of power and mixture setting does not seem real. At the same altitude, pulling power must reduce CHT. Oil is harder to sort out since it could have multiple causes. I would focus on understanding the CHT first.

      Eric

      #96432
      bthomason
      Participant
        quote EPANNING:

        For the ground cooling issues have either of you tried a higher rpm and very LOP?

        It helps some, but temps are still very high. The internal cowl flaps on the 303 are a strange animal. It really should have traditional cowl flaps.

        #96441
        bthomason
        Participant

          John: IMC at 16,000 I was operating LOP (30″ and ~14gph) picking up some ice, not much but more than a trace and I could see a build up on the cowls around the air intake when I noticed I had lost a few hundred feet and turned 30 degrees left. Lots of brown on the AI. I immediately ran the mixtures to full rich and recovered. It was over in a flash and ATC did not notice. I looked at the JPI file on the ground and I had lost enough fuel flow to cause the engine to loose power. I have no idea why it happened and had the alternate air door checked on the ground but nothing was found to explain it.

          Tony’s Reponse: I’m not sure either, but I will say that when running LOP, it is a “cat’s whisker” from an engine running and not running. In fact on many twin Cessna’s several people have reported that they are unable to run LOP because with the “click” style mixture control one click is a little too rich and the next “click” is engine off.

          Just throwing this out there, maybe the inlet air lip ice somehow interrupted the airflow to the turbo enough that the turbo Upper Deck Pressure (UDP) sagged and the fuel pump (that is referenced to the UDP) went down scale slightly as a result. This is not a previously observed phenomenon on my part but just a SWAG.

          Tony

          #96455

          Tony thanks for the thoughts that seem to me to be the most likely issues. I would add that it is essential to take time to get the TIT to settle to a stable peak temperature. And again to set it at 50-70 LOP as it is easy to get it too lean if you reduce mixture too quickly. I then repeat the procedure after 15 minutes as the engine temperatures stabilizes and monitor TIT and fuel flow on the JPI. I find fuel flow as little as 1 gph less than 70F LOP can cause the engine to go into a mixture shut down so care is needed. Thanks, John

          #96456

          High CHT/oil temp at 17,000 irrespective of power and mixture setting does not seem real. At the same altitude, pulling power must reduce CHT. Oil is harder to sort out since it could have multiple causes. I would focus on understanding the CHT first.

          Eric,
          I agree it does not make any sense but it happened and I have not seen it repeated. It was a hot day over Las Vegas on the way to Flagstaff. CHTs went close to 400 which is the red flag level according to GAMI. Maybe if I had waited longer for a power reduction to take effect it would have helped but the CHTs were too high so I descended. I was surprised that a few thousand feet showed reduction in CHT and likely it was a combination of the 2 actions. I agree oil temp was a secondary issue. Root cause I think is airflow and weak cowl flaps for which I would love to have a solution. A 337 for traditional 400 series cowl flaps would likely solve the problem. Thanks, John

          #97049

          I noticed some high CHT’s when I first purchased my 303. What worked for me was making new baffles from silicone rubber and taking the time to fit them just right.
          A flashlight behind the baffles will help you check for fit. When you get a chance take a look under the cowling of one of the new Cessna singles. They must use two tubes of caulk to fill all the gaps. I filled some of the gaps with silicone (around the mags etc). I have the original temp gauges and then an engine analyzer. I would believe the analyzer and it takes time to get
          the engines up to 200. Even in hot high climbs temp top out at about 360. If they want to work higher than 380 I just lower the climb rate for a bit. Continental has an piece on line about
          making sure that the lower cheek baffles are placed properly or the engine warranty is void. FYI, I always leave the cowl flaps open unless it is really cold and I have a long descent.

          hope that this helps.

          tom

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