High CHT on number 1

P

Pfitmx15

Pre-Flight
Joined
Apr 10, 2012
Messages
57
Display Name
Display name:
Pfitmx15
Hey guys I have a 1980 Piper Archer. I flew it 12 hours to Oshkosh and back and noticed CHT around 450 in the climb and it would settle in cruise running 100’ ROP to 380-400. When I got back I checked the baffles and they were shot. My mechanic and I got a new kit of the silicone baffle materials that were cut for the archer. Installed and they look and fit great. Also used ultra copper RTV to seal any gaps in the steel and between the case and bottom of the baffle steel.

Test flew it last night with mixed results. The highest CHT I got on climb was 420. In cruise I got 350-360 which is noticeably better. However cylinder number 1 stayed at 400 in cruise. I did not fly for a long time as I was up against time wise. What I did notice however was that my differitial in EGT was down to 50-60. The best I could do coming back to Oshkosh was 90-100. My question is if the EGT are that close is there a chance that the probe in number one is in error? How do they fail (meaning do they show hot when failing or do they just quit working all together) its a JPI 700 with the bar graph and digital read out. The mechanic wants to pull a spark plug and look for a leak or crack near the valve. I also think we should switch probes before we do all that. Finally at Oshkosh I went to a lycoming class and they said to avoid prolonged operation above 400. Does that mean it’s okay on climb out to be above as long as I stay under the rest of the time? Should I even be worried that the CHT in one is 390-400? Engine stats. 950 SMOH lycoming factory reman although it was done in 2002. Oil analysis has been great and it just came out of annual with compressions 78 on all four jugs. Anyways thanks for the help. Before and after pics on the baffles below.
521bcaa93847adcf8400aa6fbf5eac6e.jpg
af45480c0687ae7ef7d6f1ecc15e545b.jpg
f8f6f4be54dc2c8935935022be70e58a.jpg
2fc43f3eef97418126e3193d131e406f.jpg



Sent from my iPhone using Tapatalk
 
Pull a bottom (more likely than top, but what the heck, pull both) spark plug and look for a clinker of lead stuck in the base. Start with the cheap and easy.
Nice job on the baffle seals.
 
Getting the old baffle staples out was a behoch.... I know this!
 
I’m pretty sure I ruined my dikes getting the staples out. My hand was killing me afterwards!


Sent from my iPhone using Tapatalk
 
We have dealt with CHT1 temps going above 400 on takeoff for a while now on our O-540. We swapped probes, with no change. Initially considered that it might be an induction leak but we didn't do anything about it as everything is working too go to mess with the engine (~2400 since TBO). Buddy at SNF was told to zero his numbers on the probes in the system, to basically reset numbers, perhaps errors from the manufacturing process of the probe but that would seem to be resolved with swapping probes.

Good luck chasing down the gremlin. If you can get the temps to stay normal in cruise then it might not justify the cost of changing a cylinder just to be extra sure. Our mechanic (who has 18 rentals without JPIs) has blamed the amount of info we have in the JPIs. Seems planes just fine when we didn't have way too much info to distract us.
 
#1 has the outlet for the oil cooler hose right above it. That causes a slightly lower pressure above that cylinder and it will run hotter anyway.

But the CHT probe should be checked for accuracy anyway.
 
Dan Thomas said:
#1 has the outlet for the oil cooler hose right above it. That causes a slightly lower pressure above that cylinder and it will run hotter anyway.

But the CHT probe should be checked for accuracy anyway.
Click to expand...

I saw the outlet for the oil cooler but don’t you think 3 would run hot also? 1 does have all of the A/C gear in front of its bottom end.


Sent from my iPhone using Tapatalk
 
#1 on a Lycoming? My #1 has the coolest CHT by a good margin, as I’d expect. I have nothing to offer for why yours would be hot. I’m interested in what you find, though. How do your EGTs compare?
 
Stewartb said:
#1 on a Lycoming? My #1 has the coolest CHT by a good margin, as I’d expect. I have nothing to offer for why yours would be hot. I’m interested in what you find, though. How do your EGTs compare?
Click to expand...

Egt is within 60 degrees of each other with number one in the middle


Sent from my iPhone using Tapatalk
 
Guarantee? Lycoming says 500 is redline but 400 is the normal operations limit for long engine life. Continental uses 460 for redline but also likes 400 for normal ops. Nobody would use 500* as a cruise temperature but according to Lycoming an occasional CHT in the high 400s is not a problem.
 
Dan Thomas said:
The TCDS lists the redline CHT as 500°F.
Click to expand...
No, catastrophic failure is 500 F. The #3 (O360 product line, back cylinder starboard) traditionally runs hot because it's in front of the oil cooler. This is a characteristic of the engine model. Keeping below 450 in climb, then below 400 in cruise, as per the Lycoming documentation. Hot summers, cruise is a bit more difficult to manage but still keep below 400.

New baffling definitely a good idea.
 
I spent about 30 minutes looking up CHT limits after my dad chewed me out for over 400 in climb on the O320 which had a 510 limit, citing Mike B generalities. Continentals generally have a lower CHT limit than Lycoming except the C75 which has a smoking hot red line CHT of 550 degrees F.

I think Ted mentioned a while ago that CHT limits are really about detonaton prevention not metals yielding. That said I'm careful about CHT, staying about 80F or more under max during all climbs
 
Pfitmx15 said:
Egt is within 60 degrees of each other with number one in the middle


Sent from my iPhone using Tapatalk
Click to expand...

Interesting that our EGTs (comparing small apples and big apples) are higher on 1 & 4. CHT on #1 will creep up to 400 at full power even at 10K. Always been curious but nobody has had any solid ideas and we don’t want to change anything so we fly to the numbers. Little richer or a little less power which is limited at our normal cruising altitudes anyway.
 
Dan Thomas said:
It's in the TCDS for the engine, not the airframe.
Click to expand...

Found it. Looked at the 182 TCDS first and I got the sadz. Now to go back and troll the guy who posted the 360 TCDS when I specified mentioned that I was comparing little apples and big apples (360 vs 540).
 
1RTK1 said:
Will your engine run lean of peak?
Click to expand...

Haven’t tried. Most I’ve read about it is that since it’s carbureted it’s hard to ensure equal fuel flow to each cylinder compared to fuel injection models. May give it a try anyway sometime



Sent from my iPhone using Tapatalk
 
Aluminum should never get over 400º. Cylinders running over 400º suffer from metallurgical changes in the aluminum. There are several very good Pelican Peak and Mike Bush articles about this.
 
NordicDave said:
Aluminum should never get over 400º. Cylinders running over 400º suffer from metallurgical changes in the aluminum. There are several very good Pelican Peak and Mike Bush articles about this.
Click to expand...
Depends on the cylinder pressures, probably. My A-65 has a max CHT of 550°F. Same sort of aluminum head.
 
At something like 600* aluminum loses 50% of it strength if I remeber right. Although at temps close to that you are going to have some major problems anyway.
 
bnt83 said:
I'm sure the aluminum pistons are running way over that, including the inside surface of the combustion chambers
Click to expand...

Yes pistons can, although I can’t remember the exact numbers, the boundary layer adds much protection from the multi thousand degree heat of combustion.
 
NordicDave said:
Aluminum should never get over 400º. Cylinders running over 400º suffer from metallurgical changes in the aluminum. There are several very good Pelican Peak and Mike Bush articles about this.
Click to expand...

bnt83 said:
I'm sure the aluminum pistons are running way over that, including the inside surface of the combustion chambers
Click to expand...

I should have been more clear. The aluminum alloy used in the cylinders.
 
Annealing should be done at 775°F for at 2 to 3 hours at temperature,
 
You must log in or register to reply here.
Back
Top