Tommy Posted May 15, 2018 Report Share Posted May 15, 2018 Hi everyone! My 1981 J's #2 is, on average 30 to 35-degree hotter than every other cylinders (355-360 vs 325) running LOP. Wonder if there is any way I can bring this down (like the baffle mod for #1) so it's the same temp as all others. Then I can run all of them bit closer to 350 in cruise for better fuel burn. The compression on it is 76 and it peaks first. The baffle is brand new with good seal. Also it seems like it's getting hotter as well. It used to be 20 to 25 hotter than the others (345-350 vs 325) now it's 30 to 35. Is this a cause for concern? Thanks guys! Quote Link to comment Share on other sites More sharing options...
INA201 Posted May 15, 2018 Report Share Posted May 15, 2018 In my 1978 J with good baffling has a hot #1. It is the last to peak so technically it is running with more power than the other three LOP. I’ve considered buying a new nozzle and see if it balances out. In your case the #2 should be the leanest of your cylinders since it peaks first. I would think that it certainly should be cooler than the other three cylinders all things being equal. I had a very small exhaust leak at one point that would blow onto one of the temperature probes that made the temperature reading too high. I found it simply by looking at the inside of the cowling and there was a melted piece of conduit and some black residue on the inside of the cowling near the probe. It was an easy fix. I’ve heard of others with the same problem. I would start there first. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 15, 2018 Report Share Posted May 15, 2018 Hot CHTs are a dynamic balance of energy in vs energy out... and a test of the TC... 1) See if the hot CHT is being caused by an overly lean (ROP) EGT for that cylinder... 2) Then See if the heat isn’t being removed as well for that cylinder... cooling baffles not sealing very well... 3) Then there is the reality check... is the CHT really getting hot or is it just a thermocouple probe not functioning as well as it should. 4) post pics of your JPI graphs if able... 5) post pics of your TC that is running hot... is it one of those rings under a spark plug, or other ring styled piggyback TCs? 6) Sometimes maintenance induced changes can cause CHT challenges... real or indicated... PP ideas only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
mooneyflyer Posted May 15, 2018 Report Share Posted May 15, 2018 Another quick check is to swap CHT sensors and see if that’s the issue. Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted May 15, 2018 Report Share Posted May 15, 2018 +1 on swapping sensors. Does anyone know if all M20J's have the factory CHT in the #3 cylinder, or does this from plane to plane? Quote Link to comment Share on other sites More sharing options...
Jeev Posted May 18, 2018 Report Share Posted May 18, 2018 On 5/15/2018 at 1:41 PM, jaylw314 said: +1 on swapping sensors. Does anyone know if all M20J's have the factory CHT in the #3 cylinder, or does this from plane to plane? I could be wrong but every J including mine I’ve seen has one on #3. As stated above I would definitely start with swapping the sensors and go from there. Could save you some trouble shooting money. Quote Link to comment Share on other sites More sharing options...
Jeev Posted May 18, 2018 Report Share Posted May 18, 2018 Also take a good look at your baffles for any “modification” by previous owners. Check the one on the front of cylinder 1 it should go about 1/2 way up the cylinder -!: also take a look at the baffle / scoop for the oil cooler for signs of modification or bending. Next with the top and bottom cowl on take a flash light and look in / under the cowl through the air intakes at how the rubber baffle seals are resting on the inside of the cowl. They should be fairly uniform and flat with minimal wavy ness and creasing to make a tight seal. Lastly make sure the hard baffles around the front of the engine are sealed up with RTV and there are no gaps. Fixing these issues on my J made a big difference in CHT’s and was relatively easy. You may not think the little baffle on cylinder 1 or a little gap here and there makes a difference but it does as the air moving through the cowling does some interesting things. If all that fails adjust your cowl flaps to trail about 1/2 - 1in open in the closed position and see if that gets you in a range where you are happy. Good lucK. Quote Link to comment Share on other sites More sharing options...
Guest Posted May 18, 2018 Report Share Posted May 18, 2018 On 5/15/2018 at 7:03 AM, Tommy said: Hi everyone! My 1981 J's #2 is, on average 30 to 35-degree hotter than every other cylinders (355-360 vs 325) running LOP. Wonder if there is any way I can bring this down (like the baffle mod for #1) so it's the same temp as all others. Then I can run all of them bit closer to 350 in cruise for better fuel burn. The compression on it is 76 and it peaks first. The baffle is brand new with good seal. Also it seems like it's getting hotter as well. It used to be 20 to 25 hotter than the others (345-350 vs 325) now it's 30 to 35. Is this a cause for concern? Thanks guys! Hi Tommy, What type of CHT thermocouple do you have? If it’s a spark plug gasket type this could account for the difference you’re seeing. As other have said baffle sealing is vital. Clarence Quote Link to comment Share on other sites More sharing options...
Tommy Posted May 19, 2018 Author Report Share Posted May 19, 2018 Hi @M20Doc CHT2 has the proper CHT probe, I will double check the baffle sealing as well as swapping the probe to see Thanks everyone! Quote Link to comment Share on other sites More sharing options...
tony Posted May 20, 2018 Report Share Posted May 20, 2018 My number 2 used to run hotter than the rest too. The change I made was to make sure the baffle in the front of the cylinder doesn't have an air tight fit and that a little air can sneak past it in the front. The way that cylinder in made, if you have silicone sealed the baffle to the engine, it's easy to block the airflow through the front fins. 1 Quote Link to comment Share on other sites More sharing options...
Tommy Posted May 21, 2018 Author Report Share Posted May 21, 2018 On 5/20/2018 at 8:04 PM, tony said: My number 2 used to run hotter than the rest too. The change I made was to make sure the baffle in the front of the cylinder doesn't have an air tight fit and that a little air can sneak past it in the front. The way that cylinder in made, if you have silicone sealed the baffle to the engine, it's easy to block the airflow through the front fins. Can I trouble you with a photo to go with your description please? Thanks Tony! Quote Link to comment Share on other sites More sharing options...
INA201 Posted May 25, 2018 Report Share Posted May 25, 2018 Since Tommy started this thread I’ve been observing my #1 a little closer. It peaks last, runs higher CHTs when other 3 are LOP etc. is there merit to starting with a flow test first and go from there? Quote Link to comment Share on other sites More sharing options...
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.