DXB Posted October 29, 2015 Report Posted October 29, 2015 What Ross and M20F say here makes some sense to me. I'm also interested in the EGT/CHT relationships that other C or G model pilots are seeing in climb. Just for fun, I'm posting my EGT/CHT climb profiles from two flights on the same day under very similar conditions, each time climbing to 2500 AGL. In #1, cyl 3 runs the hottest, peaking in the 430s, with a high EGT (1400), but #4 just touches 400 and has a much lower EGT. In flight #2, the situation reverses, and #3 runs much cooler. Note when I level off and set power to 23 squared, the CHT/ EGT picture is drastically different and very benign looking. BTW my oil temps are running 180s-190s on these flights- pretty much ideal from what I understand. I'm gonna ask Mike Busch on this one... Quote
M20F Posted October 29, 2015 Report Posted October 29, 2015 Looking at the graphs it seems about 2 mins from take off to 2500 feet where you adjust power/mixture? Quote
Shadrach Posted October 30, 2015 Report Posted October 30, 2015 That is also another difference in the two. The oil cooler on a parallel valve engine is a single pass while the angle valve engines use a dual pass. ok, but do you think that 14XX on take off is optimal in this engine. Quote
Shadrach Posted October 30, 2015 Report Posted October 30, 2015 What Ross and M20F say here makes some sense to me. I'm also interested in the EGT/CHT relationships that other C or G model pilots are seeing in climb. Just for fun, I'm posting my EGT/CHT climb profiles from two flights on the same day under very similar conditions, each time climbing to 2500 AGL. In #1, cyl 3 runs the hottest, peaking in the 430s, with a high EGT (1400), but #4 just touches 400 and has a much lower EGT. In flight #2, the situation reverses, and #3 runs much cooler. Note when I level off and set power to 23 squared, the CHT/ EGT picture is drastically different and very benign looking. BTW my oil temps are running 180s-190s on these flights- pretty much ideal from what I understand. I'm gonna ask Mike Busch on this one... Your fuel flow seem to be less than book by nearly a full GPH. Quote
M20F Posted October 30, 2015 Report Posted October 30, 2015 ok, but do you think that 14XX on take off is optimal in this engine. Why do you think 14xx is bad? Absolute EGT up to a point p (i.e. EGT of 5000 degrees would be a bit suspect) is viewed largely as irrelevant. I would agree that fuel flow is low using a rough thumb of 10% of horse power. Riching things up a bit and seeing what that did to the CHT would be where I would start for sure. Quote
Shadrach Posted October 30, 2015 Report Posted October 30, 2015 (edited) On October 30, 2015 at 8:19 PM, M20F said: Why do you think 14xx is bad? Absolute EGT up to a point p (i.e. EGT of 5000 degrees would be a bit suspect) is viewed largely as irrelevant. I would agree that fuel flow is low using a rough thumb of 10% of horse power. Riching things up a bit and seeing what that did to the CHT would be where I would start for sure. everyone always says absolutely FF doesn't matter. For the most part that's true. Can we agree that a full rich wide open throttle take off should be ~ 250° ROP or more? Do you think 1425° is 250° ROP? Have you ever seen a properly timed normally aspirated engine produce a 1675° EGT with both plugs firing? Absolute EGT does mean something in some cases. I personally don't believe that cylinder will peek at 1675. In fact, it's my contention that his #3 cylinder is within ~100° of peak on take off. Edited February 10, 2016 by Shadrach Quote
jrwilson Posted October 30, 2015 Report Posted October 30, 2015 Hello, I have been thinking about this high cht issue for a while and here are my thoughts. First, I still have yet to hear from anyone with a "c" model fitted with a 4 channel digital engine analyzer who isn't seeing high cht's (greater than 400) on best rate climbout. My C model has been thoroughly gone through (baffles perfect, etc.) and will produce 450 deg. cht's if I let it by not shallowing climb to get greater than 120 mph. If I do this I can keep cht's around 400 then about 360 in cruise. I have read a lot about cowl design and I can tell you Mooney really screwed up on the "C" model. The inlet holes are too large even with the cowl closure which mine has, the upper plenum volume is too small, the cowl flaps are too small, and the oil cooler airflow raises the pressure in the lower cowl making airflow even less efficient. Do a Google search on "M20C evaluation report". Here you will find a series of tests conducted several years ago with a well maintained 1965 M20C. Included in the article is a chart and in this chart you will notice CHT's as high Rich Taracka A&P IA I had a 63 m20c with a cowl closure. I had a jpi 700 and installed a jpi 900 later. I live in California and with OAT of 90 plus, extended climbs to 10k plus I routinely saw cht at 380, maybe 390 if it was really hot. Never as hot as 400 except when I first bought the plane. Did lots of work sealing the doghouse and temps came down. Granted that isn't extended Vx, because why would anyone do that? That's at 105 to 115 mph indicated. But even the initial climb, not above 380-390. So now you have heard from a C owner (former) with a 4 channel gem and the temps don't have to be as hot as all that. Sent from my iPhone using Tapatalk Quote
M20F Posted October 30, 2015 Report Posted October 30, 2015 everyone always says absolutely GT doesn't matter. For the most part that's true. Can we agree that a full rich wide open throttle take off should be ~ 250° ROP or more? Do you think 1425° is 250° ROP? Have you ever seen a properly timed normally aspirated engine produce a 1675° EGT with both plugs firing? Absolute EGT does mean something in some cases. I personally don't believe that cylinder will peek at 1675. In fact, it's my contention that his #3 cylinder is within ~100° of peak on take off. It's a carbureted engine so getting 250 ROP to all cylinders or any consistency is going to be very different than an injected engine. You also see two different cylinders peak at this number on essentially the same day so there could be issues with the carb or other things, I wouldn't fret so much over the 1400 reading itself. Hard to troubleshoot over the Internet, I would certainly take the engine data and the plane and review with my mechanic. Making the carb run a bit richer would be probably where I would start because the fuel flow does seem low and starting with easy and cheap is always the best place to begin. Quote
DXB Posted October 30, 2015 Report Posted October 30, 2015 (edited) Looking at the graphs it seems about 2 mins from take off to 2500 feet where you adjust power/mixture? Closer to 3-3.5 minutes. Didn't lean much or find peak. Making the carb a bit richer seems a reasonable place for a mechanic to start. I think that's just turning a screw if I recall. Edited October 30, 2015 by DXB Quote
Shadrach Posted October 30, 2015 Report Posted October 30, 2015 It's a carbureted engine so getting 250 ROP to all cylinders or any consistency is going to be very different than an injected engine. You also see two different cylinders peak at this number on essentially the same day so there could be issues with the carb or other things, I wouldn't fret so much over the 1400 reading itself. Hard to troubleshoot over the Internet, I would certainly take the engine data and the plane and review with my mechanic. Making the carb run a bit richer would be probably where I would start because the fuel flow does seem low and starting with easy and cheap is always the best place to begin. I fully understand the shortcomings of carburetors. Getting the leanest to 250 is the point, some will have to be richer. The oft repeated phrase "raw EGT numbers don't mean anything" is often taken to its most literal end. It is meant to help folks get over the fact that cylinders peak at different EGT numbers but similar FF. As in "my GAMI spread is .01 but my EGT spread is 75"... "Don't worry, raw EGT number don't matter". It does not mean don't worry about the numbers when the numbers are clearly telling you something. If I took off with a buddy and noticed all of his EGTs were over 1600, I wouldn't say, "don't worry raw EGT numbers don't matter"... I'd say, "you have a dead mag, let's return immediately"... We know that N/A O360 with a healthy ignition system will not produce a peak EGT much over about 1525. Given that we know this, we can deduce that a 1400df EGT under the best scenario translates to 125df ROP. That is not a good place to run an engine on take off or during climb. We can support this hypothesis by looking at the book numbers Hank posted from his M20C POH. They show a WOT 2700rpm full rich FF of 18.2 at SL on a standard day. If Dev's FF is to be believed he was only getting 17.6 on a day slightly cooler and higher pressure than standard. .6gph is significant and will have a significant effect on both EGT and CHT. if you still feel that I'm confused, perhaps you might email Mr. Busch or Mr. Braly or Mr. Atkinson. I feel certain their answers will be similar, but I've been wrong before... Quote
M20F Posted October 30, 2015 Report Posted October 30, 2015 I didn't say you were confused but to me it is impossible to draw much from the two graphs. You have two cylinders on the same day with the same conditions exhibiting very different EGT's which can mean there is an induction issue, issue with carb, leak, etc. You have high CHT's which could come from improper fuel/air mix, baffling, to low IAS in climb, etc. The CHT or EGT probes could be installed incorrectly to where everything in the graphs is bunk. The Internet is a great place for ideas but just like I wouldn't advise diagnosing cancer on WebMD, I wouldn't diagnose this type of a problem on a forum beyond some ideas to discuss with my mechanic. Without seeing the plane and all the details it's hard to say what is happening. To me 14xx EGT isn't super alarming, the fuel flow looks off and that would be a cheap/easy starting point. Quote
Shadrach Posted October 30, 2015 Report Posted October 30, 2015 You bring up a good point about possible induction leaks. That is another area to pursue. If a 14XXdf take-off EGT isn't alarming, is there a take-off EGT that would alarm you? Im not suggesting FF is the sum of the problem, but it is low hanging fruit. Quote
M20F Posted October 30, 2015 Report Posted October 30, 2015 You bring up a good point about possible induction leaks. That is another area to pursue. If a 14XXdf take-off EGT isn't alarming, is there a take-off EGT that would alarm you? Im not suggesting FF is the sum of the problem, but it is low hanging fruit. Anything that is different from what I normally see would concern me, I don't know what he normally sees and 14xx isn't a wildly crazy number. Riching things up is the easiest first route. The fact that the #3 and #4 cylinders swap EGT numbers on a same day back to back flight is a bit bizarre but without more data hard to tell much from it (could be fouled or bad plugs, again not enough info to make conclusions). Quote
carusoam Posted October 30, 2015 Report Posted October 30, 2015 Additional data points... 1) Back in the day raw EGT data was considered less important because of variation in location from field installed sensors. 2) Modern Mooney installations have a single EGT installed in the exhaust where it sees the 3 into 1 flow. Essentially seeing half the engine, not just one cylinder. 3) POH procedures use the single EGT to lean in the climb. The simple EGT gauge is marked with a blue box. Keep the needle in the box during the climb. The box is 100°F wide and includes 200°ROP in the range. The modern gauge is actually marked in °F. 4) The act of standardized installation has made exact use of raw EGT data very useable. 5) The act of performing engineering work and publishing it in a POH has made it useable . ------------------------------ 6) High EGTs are often caused by fuel still burning as it exits into the exhaust. The run-up mag test demonstrates this well. Kill one mag all four (or six) EGTs rise. A leaky valve or faulty plug would stand out compared to the others. 7) The O360's carb has two fuel nozzles. The main one is always flowing. The secondary one is supposed to flow when at WOT. With good FF and EGT data the secondary nozzle should be visible. I could never detect it with the factory installed gauges in my M20C. 1 Quote
carusoam Posted October 30, 2015 Report Posted October 30, 2015 Ran out of space... Best regards, -a- Quote
Oscar Avalle Posted February 9, 2016 Report Posted February 9, 2016 Just an additional point on high CHTs on climb. I have been experiencing high CHTs for a while. I did everything I could do to get them down. New doghouse, climb at 120 mph, timing,you name it... today I spoke to Don Maxwell and shared with him my frustration about my CHTs. He asked me about my carburetor. I gave him the s/n 10-4164-1. Interestingly he got back to me and said that that was not the right carburetor for my M20C. The right part number is 10-3878M (M stands for Mooney). There is even and SB out there asking owners with a 10 3878 to change it to a M version. I ordered the new carb and hopefully I will get it before the end of the week and be able to report back next week if that has helped... Oscar 2 Quote
gsxrpilot Posted February 9, 2016 Report Posted February 9, 2016 Still following this thread closely. Quote
Oscar Avalle Posted February 9, 2016 Report Posted February 9, 2016 On 10/30/2015 at 11:26 PM, Shadrach said: I fully understand the shortcomings of carburetors. Getting the leanest to 250 is the point, some will have to be richer. The oft repeated phrase "raw EGT numbers don't mean anything" is often taken to its most literal end. It is meant to help folks get over the fact that cylinders peak at different EGT numbers but similar FF. As in "my GAMI spread is .01 but my EGT spread is 75"... "Don't worry, raw EGT number don't matter". It does not mean don't worry about the numbers when the numbers are clearly telling you something. If I took off with a buddy and noticed all of his EGTs were over 1600, I wouldn't say, "don't worry raw EGT numbers don't matter"... I'd say, "you have a dead mag, let's return immediately"... We know that N/A O360 with a healthy ignition system will not produce a peak EGT much over about 1525. Given that we know this, we can deduce that a 1400df EGT under the best scenario translates to 125df ROP. That is not a good place to run an engine on take off or during climb. We can support this hypothesis by looking at the book numbers Hank posted from his M20C POH. They show a WOT 2700rpm full rich FF of 18.2 at SL on a standard day. If Dev's FF is to be believed he was only getting 17.6 on a day slightly cooler and higher pressure than standard. .6gph is significant and will have a significant effect on both EGT and CHT. if you still feel that I'm confused, perhaps you might email Mr. Busch or Mr. Braly or Mr. Atkinson. I feel certain their answers will be similar, but I've been wrong before... Interesting... thank you. Now things start falling into place... If indeed WOT 2700 RPM translate into fuel flow of 18.2... I am just getting 16.5 that explains a lot why my CHT are going through the roof... and it consolidates the hypothesis that I have the wrong carburetor. 1 Quote
Oscar Avalle Posted February 9, 2016 Report Posted February 9, 2016 On 10/27/2015 at 1:14 PM, N9495V said: Oscar – Similar to you I have done a lot of work to improve my cooling and still not where I would like to be. Changing the plugs didn't help. Obviously being based in the desert amplifies the problem. Do you have a powerflow exhaust and what is your fuelflow during takeoff / climb. Also my 1970 model (Serial number +61 compared to yours) doesn’t have the channel on the aft side of the cowling, where the lower baffling strip rests – does yours? Frank Frank, just saw your post... sorry traveling too much.. I have powerflow exhaust. My fuelflow during takeoff is only 16.5 takeoff and climb 15.3 I understand that this is too low and it just does not give you enough cooling. Quote
DXB Posted February 10, 2016 Report Posted February 10, 2016 47 minutes ago, Oscar Avalle said: Frank, just saw your post... sorry traveling too much.. I have powerflow exhaust. My fuelflow during takeoff is only 16.5 takeoff and climb 15.3 I understand that this is too low and it just does not give you enough cooling. I just went through looking into at these issues on my carb at annual - mine gets 17.2 -17.6 FF at WOT at low DA. No easy way to adjust mixture at high power on the carb itself, just idle mixture which is irrelevant above 1500rpm. Make sure pushing your mixture control to full rich maxes out the travel of the connection on the carb- this was not my problem. There are 3 approved variants of our carb with differing set mixtures. Figuring out which one you have is a good place to start but may require a call to Marvel Schleber with the numbers off the carb. Doing anything more likely means pulling the carb which is a major job. Their suggested overhaul interval, which most folks ignore, is 10 years. On advice of my MSC I elected not to pull my carb. They made some minor improvements to my baffling (there's still a lot of room for improvement) and this did help cooling significantly. I then personally changed my high resistance champion plugs to "cooler" tempest plugs but noted no additional benefit. Quote
par Posted February 10, 2016 Report Posted February 10, 2016 I'm going to have my carb looked at as well along with the baffling. My next plane purchase won't be a C for a number of a reasons with this issue being one of them. You would think it would have been figured out and solved on a 50+ year old airplane that has been in flying condition most of its life. Quote
Shadrach Posted February 10, 2016 Report Posted February 10, 2016 (edited) 25 minutes ago, DXB said: I just went through looking into at these issues on my carb at annual - mine gets 17.2 -17.6 FF at WOT at low DA. No easy way to adjust mixture at high power on the carb itself, just idle mixture which is irrelevant above 1500rpm. Make sure pushing your mixture control to full rich maxes out the travel of the connection on the carb- this was not my problem. There are 3 approved variants of our carb with differing set mixtures. Figuring out which one you have is a good place to start but may require a call to Marvel Schleber with the numbers off the carb. Doing anything more likely means pulling the carb which is a major job. Their suggested overhaul interval, which most folks ignore, is 10 years. On advice of my MSC I elected not to pull my carb. They made some minor improvements to my baffling (there's still a lot of room for improvement) and this did help cooling significantly. I then personally changed my high resistance champion plugs to "cooler" tempest plugs but noted no additional benefit. Dev, I think the reason that you are seeing changes in which cylinders are hot in climb and which are hot in cruise has to do with "pulling back" to 23 squared. This does 2 things. 1) In theory it should allow you to run slightly richer on all cylinders. 2) cocking the butterfly into the intake stream when you "choke" the engine back to 23" creates turbulence in the intake and could change how your cylinders peak when compared to wide open throttle. Either way, the goal should be to get enough fuel into the engine at WOT. There should be no need to "pull back to" anything unless you want to go down or slow down. Edited February 10, 2016 by Shadrach 1 Quote
Hank Posted February 10, 2016 Report Posted February 10, 2016 (edited) Tru dat, Ross! I climb my C WOT/2700. For low level cruise, like a nearby lunch run or an IFR descent, 23/2300 works well for 3000 msl or so. Well leaned out, I sometimes indicate 150+ mph there. But the plane climbs really badly there; if Departure clears me to 3000, I'll loiter for a minute or two WOT, then pull back and lean; cleared higher, all three go all the way forward. If the intermediate level off is at 4000-6500, then I prefer 22"/2400. I only have temp issues on extended climbs in the summer, and then it's usually Oil temp getting high; lowering the nose 10-15 mph helps. P.S.-- I have a 3-blade Hartzell, 201 windshield and the guppy mouth closure. Will check climb temps this summer with my resurrected doghouse. Edited February 10, 2016 by Hank 2 Quote
carusoam Posted February 10, 2016 Report Posted February 10, 2016 I can only imagine what having a new carb is like. Especially a new proper one! do we have a feeling for what or how many CFM the carb can handle at WOT in the M20C? Old car thoughts and comparisons come to mind. Next question is about the diameter of the throttle plate? these are all measurements related to volume of air that goes to the engine to be mixed with the FF. Best regards, -a- Quote
StinkBug Posted February 12, 2016 Report Posted February 12, 2016 On 2/9/2016 at 0:17 PM, Oscar Avalle said: Just an additional point on high CHTs on climb. I have been experiencing high CHTs for a while. I did everything I could do to get them down. New doghouse, climb at 120 mph, timing,you name it... today I spoke to Don Maxwell and shared with him my frustration about my CHTs. He asked me about my carburetor. I gave him the s/n 10-4164-1. Interestingly he got back to me and said that that was not the right carburetor for my M20C. The right part number is 10-3878M (M stands for Mooney). There is even and SB out there asking owners with a 10 3878 to change it to a M version. I ordered the new carb and hopefully I will get it before the end of the week and be able to report back next week if that has helped... Oscar I hope this works for you, but I wouldn't get too excited just yet. My C is in for annual right now and I checked this morning and I have the same carb as you, but none of your issues. On a 90 degree day I might see 410 on one cylinder on climbout if I'm heavy and slow, but almost never do I see over 400. Most of the time I'm in the low 300s. I haven't really paid that much attention to fuel flows because temperatures matter more to me, and mine are never hot, but I'll watch next time to see. FWIW my cruise EGT is right around 1300, and full rich on takeoff is significantly cooler. Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.