dtoelke Posted March 13, 2015 Report Posted March 13, 2015 I went to run up my 231 today after fixing a small oil leak in one of the oil cooler bolts (cowling off). After a couple minutes at 2000 rpm, I notice cylinder 4 is getting unusually hot (coming up on 380 which is my personal threshold) and I'm at full rich. All of the other cylinders are stabilized between 300-330 (normal). I pull the throttle back until the engine is at 1200 rpm, and while all of the other cylinders start cooling down number 4 continues to climb. It wouldn't start cooling until I had the engine below 1000 rpm. I ran it up three days ago to find the leak for about 10 minutes with no issues whatsoever. Here are a couple of other observations: 1) The cylinder was replaced 30 hrs ago 2) I performed a mag check and EGT's rose in both cases (mags good) 3) EGT's overall seemed a little higher on cylinder 4 but I'm usually in normalized mode for the runup and don't often look at absolutes so I'm not sure if that's an anomoly 4) I switched the probes for 2 and 4 and confirmed it's not the sensor (still saw the overheating on the probe in #4) 5) I noticed the edge of the outermost cooling fin on the cylinder is broken off (pic below) and the fins behind it are bent inward as if something hit them. I'm not sure how that happened (seriously I can't figure out how unless somebody hit it with a screwdriver or something. it's protected by the exhaust manifold. The cylinder is only a month old, but perhaps it happened some other time and I hadn't noticed it until today. However, I don't think this should have a significant impact on cooling or the prob readings. http://mooneyspace.com/gallery/image/36483-/ All of the evidence at this point suggests a plugged injector, but I just had GAMI's installed about 30 hrs ago and I've flown a couple times a week since. Tomorrow I'm going to pull the injector with my mechanic and check it out, but I'm wondering if anybody has any other thoughts before we start. Any help would be greatly appreciated! Quote
kmyfm20s Posted March 13, 2015 Report Posted March 13, 2015 I see that the cooling shield wedge between the broken cooling fins but that looks suspicious to me. I not sure where the cylinder/head junction is on those cylinders but I would check for a possible separation crack just to rule that out. Otherwise clean injectors, check for induction and exhaust leaks. Quote
carqwik Posted March 13, 2015 Report Posted March 13, 2015 Plugged injector would be my guess... Just 'cause you didn't experience it on a prior flight doesn't mean your injector didn't get clogged somehow since the last shutdown. BTDT. Had my local wrench (great guy btw...knows his stuff) take a look after I described a very high CHT (and low EGT) during my initial climb...right away he said it was the injector. Sure enough, found a speck of some kind (like the size of a grain of sand) in the injector...doesn't take much to cause a problem. Problem was easily and correctly resolved. Quote
M20Kid Posted March 13, 2015 Report Posted March 13, 2015 Just a thought; you said you did the runup at full rich. Restart the engine and let it stabalize as before, then start leaning. If that injector is plugged and the fuel flow is reduced already, then that cylinder should drop off much sooner than the others. Seems a simple test before tearing anything apart. Quote
mooniac15u Posted March 13, 2015 Report Posted March 13, 2015 Cooling is unpredictable without the cowling on. Before you spend too much time chasing this you might want to put the cowling back on and see if it is still a problem. Quote
dtoelke Posted March 13, 2015 Author Report Posted March 13, 2015 I ran it up a couple other times earlier in the week without the cowling on. No problems then. M20Kid, I didn't explain that very well. The cylinder never stabilized it kept climbing, so I had to stop the runup. I did lean just to see what happened and it kept climbing. Quote
mooniac15u Posted March 13, 2015 Report Posted March 13, 2015 I ran it up a couple other times earlier in the week without the cowling on. No problems then. Were the weather conditions the same? Quote
Andy95W Posted March 13, 2015 Report Posted March 13, 2015 Check to see if you have an exhaust leak. I have seen an exhaust gasket start to leak and blow hot exhaust gases onto the cylinder head near the CHT probe. Might not be likely, but easy to check. 1 Quote
FloridaMan Posted March 14, 2015 Report Posted March 14, 2015 I should add a footer to my account with a standard disclaimer that I am a rank amateur and don't take my word for anything, but... And this may not be the issue with your own engine, it's still something that I'm cautious about. I've been told it's generally a bad idea to run the engine for very long with the cowling off. Think of it like pouring water through a comb. There is less resistance for the water to go around the teeth and not through them. While you may attribute this to surface tension, the analogy still stands with engine cooling. The area above your cylinders with the cowling on is at a much higher pressure than the area below and the air is forced through the cooling fins. Just the same as how the fan on the radiator in your car has to turn on to force air through it, the airflow from the propellor is not adequately channeled through the cylinder fins without the cowling. 1 Quote
jackn Posted March 14, 2015 Report Posted March 14, 2015 I had a similar situation a few years ago. I had just put in new champion plugs. After only a few hours, some had gone to very high resistance. They all passed the mag checks. I guess the high resistance was causing the plug to get very hot. I replaced with Tempest massives. Quote
dtoelke Posted March 14, 2015 Author Report Posted March 14, 2015 Found a small piece of gasket partially blocking the injector inflow. No idea where it came from though. Cylinder still runs fairly hot but now it's responding to changes in throttle/mixture like it should. Should be fine once the cowling is back in place. How would you recommend checking for an exhaust leak? Quote
Andy95W Posted March 14, 2015 Report Posted March 14, 2015 Visual check of the exhaust pipe right at the point where it leaves the cylinder head. Look for light grey residue that looks almost powdery. On painted areas, the paint can be scorched brown and may even appear to have bubbled. Quote
FloridaMan Posted March 16, 2015 Report Posted March 16, 2015 Found a small piece of gasket partially blocking the injector inflow. No idea where it came from though. Cylinder still runs fairly hot but now it's responding to changes in throttle/mixture like it should. Should be fine once the cowling is back in place. How would you recommend checking for an exhaust leak? Also, this is for the IO360 people, I've heard it said that on the 4 cylinder injected lycomings that it's "always* the #3 injector that gets clogged. The mechanic that told me this theorized that maybe it was how the fuel circulates in the spider and that it's #3 that gets the debris. Can anyone confirm this? And is there a similar pattern on the 6 cylinder engines? Quote
aaronk25 Posted March 16, 2015 Report Posted March 16, 2015 #3 is normally a Lean-er cylinder with #1 and 4 being the richest....so any debris or build up would be noticeable but I'd say this is a old wives tale.... Quote
mooniac15u Posted March 16, 2015 Report Posted March 16, 2015 I had a clogged #1 injector right after I bought my M20J. Quote
DrBill Posted March 16, 2015 Report Posted March 16, 2015 Found a small piece of gasket partially blocking the injector inflow. No idea where it came from though. Cylinder still runs fairly hot but now it's responding to changes in throttle/mixture like it should. Should be fine once the cowling is back in place. How would you recommend checking for an exhaust leak? PUt the output of your shop vac in the exhaust pipe. Seal with rag and duct tape. Use liquid detergent and water mix to find leaks. Works great. can do same for intake. BILL Quote
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