High CHT's

[markejackson02]

I'm having an issue with high CHT in cruise.

 

When I start the plane and take off/climb, cowl flaps open, FT/rich, CHT is 360-380 in climb, pretty normal (OAT = 92).  When I level off and run 25/25, if I close the cowl flaps the CHT's on #1, #3, and #4 are all over 400, #4 touching 450.  Running with the cowl flaps wide open gets them down ~ 390, so I left the flaps open and landed.

 

I have just fixed the top engine baffling so that it seals correctly.

 

Is there something in the bottom of the cowling that I should be looking for?  Seems like the airflow with the cowl flaps closed is obstructed or somehow compromised.

 

This is a new engine with ~20 hrs since overhaul but I would have expected the cylinders to be broken in by now with temps in a normal range.

 

Mark Jackson

M201 N201TK KAXH

 

[rbridges]

Mixture too lean, baffling not sealing somewhere or issues with the probes? What altitude are you flying and are you leaning much when you level? Did this just start?

[markejackson02]

Just installed a GEM monitor to replace the original monitor.  This is running 50 ROP at 2500 ft.  I didn't want to get too far away from the airport with the CHT that high.  Running 100 ROP got them down to 400-425.  The EGT's were in the 1400-1450 range which is similar to what my old C ran.

 

Just seems like something is fubar'ed with the air flow since opening the cowl flaps drop the temps by 70/100 degrees.

[rbridges]

Do you think it could be the probes? I sometimes have to watch oil temp at low altitudes during the summer but cht isn't usually an issue. I've never broken in a new motor so I don't know how that factors.

[Cruiser]

check the timing. It could come down a couple of degrees, that would help.

Make sure the fuel flow is at least 17 gph or higher at full power/full rich take off.

[Super Dave]

Since you are reporting reasonable CHTs in the climb, it would seem the your engine set up is OK as far as mixture, timing, baffling, and probes go. I wonder if your cylinders are not fully broken in yet. Have you seen a drop in CHTs since overhaul? If not, you may need to run full rich and with cowl flaps open until you see CHTs come down. In any case, I would avoid running 50ROP, it is the most abusive mixture setting possible.

[Andy95W]

IMO you should definitely check your lower cowling for leaks, just like your upper.

Engines cool because of differential pressure between the top and the bottom of the engine. More differential, more flow through the cylinder fins. When you open the cowl flaps, you are decreasing the pressure on the low side, which causes more air volume to flow from top to bottom.

Increasing positive pressure on the top of the engine is half the battle. If you have high pressure air going to the bottom (low pressure) side of the engine, your gains from sealing the top are negated- until you open the cowl flaps.

From personal experience, small leaks into the bottom of the cowl really add up. I've sealed leaks that were counter-intuitive (like air flowing "backwards" in the engine compartment) that ended up dropping CHT's considerably when added together.

And I also agree with the statement above that 50 deg. ROP is not a very good place to run for CHT's. Lots of good data from the GAMI guys have proven that point graphically and scientifically.

Sorry if I was preaching to the choir.

[MB65E]

Full rich!!! Don't worry about pulling it back for a while. Could adjust the cowl flaps to make sure there on spec +2* or so. Shallower climb. I'd Keep the throttle firewalled as there seems to be about 1gal+ FF more gas flowing before the change is noted on the MP gauge itself. I think they will come down, check the baffing. Seal it up really well with silicone. Oil temp staying in check?

Good luck!

-Matt

[Lood]

On that new engine and at 2500, I agree that you should be way richer than either 50, or even 100deg ROP. The fact that your CHT's rise in the cruise, IAW with much more air entering the cowling due to the higher airspeed, tells me that something is leaking or something is restricting the airflow through the cowling.

[Bob - S50]

Just installed a GEM monitor to replace the original monitor.  This is running 50 ROP at 2500 ft.  I didn't want to get too far away from the airport with the CHT that high.  Running 100 ROP got them down to 400-425.  The EGT's were in the 1400-1450 range which is similar to what my old C ran.

 

Just seems like something is fubar'ed with the air flow since opening the cowl flaps drop the temps by 70/100 degrees.

50 ROP should produce just about the highest CHT you can get.  If you go either richer or leaner from that point the CHT should drop.  I don't know about new engines, but if it were me I'd lean to about 10 or 20 LOP and see what the CHT's do.  I was up flying the other day and one of my CHT's was about 390 and slowly rising so I leaned it another 10 degrees or so and it went down to 370.  Works as advertised.

 

At 2500' I'm assuming the OAT was fairly high too.  Running 75% power at high OAT is definitely not going to help the CHT's.  If you want to run 75% power, maybe try a higher altitude like 4500' or possibly even 6500' to get a lower OAT.  You might have to use a higher RPM to get 75% power though.

 

Bob

[Hank]

I've also heard that some engines take up to 50 hours to break in. Just be patient with the break-in.

[Guest]

Mark,

In addition to the points made by others, I would ask what type of CHT probe are you using? If its the spark plug type they are not correct and will always show a value higher than actual.

Clarence

[markejackson02]

Went back today and tweaked the baffling.  I was able to get it smoothed out except for a couple wrinkles (see attached).  I observed the following:

 

Take off - full throttle/full rich/ cowl flaps open - 19.5 GPH fuel flow, EGT ~ 1250, CHT ~ 340-380.  Stayed that way through the climb to 2500.

 

25/25 Full rich - 15.8 GPH , 1325-1350 EGT, 381 Hottest CHT.

25/25 100 ROP - 12.9 GPH, 1350-1395 EGT, 405 Hottest CHT.

26/25 50 LOP - 9.3 GPH, 365 Hottest CHT.

 

So I think it is all good now, will just stay at 100 ROP until I either have 50 hrs on the cylinders or the temps drop.

 

I noted that running even a little LOP would drop the temps but the engine was a little rough.  Once everything appears broken in, will try Deakin's lean test.

 

I also used compressed air to blow out the oil cooler vanes.  It appeared to make the oil temps run a little cooler.

 

One other interesting thing.  When the baffling was initially installed and was bent backwards, cruising fast with cowl flaps open created a very noticeable vibration in the cowling.  With the baffling fixed, there is no vibration.  No real difference with them open or closed.

 

[jetdriven]

If you cut a slit (with a small amount taken out of the center in a V shape) centered on the part of the baffle that is puckered it will flatten out.

[markejackson02]

So fixing the silicone has improved things but I took a detailed look at the baffling this weekend.  Couple things popped up.  

 

There is a metal lip just under the opening for the oil cooler in the back of the baffles.  It covers half of the number four cylinder accounting for the high temps on #4.  Searching the archives, I see some folks have bent it up to allow airflow over the cylinder.  Does anyone not have this lip and if so, how does it affect the oil cooler?

 

The original drawings for the baffling show a set that is essentially open on the bottom.  The baffling on my plane is a box with the bottom half of the box blocking off airflow over about half of the cylinder fins.  Does anyone have any pictures of 201 baffles that might shed light on this?

 

Thx

 

Mark Jackson

[markejackson02]

Updating the thread after my last annual.  Boyd took apart the standby vacuum system.  The check value was all gummed up and not working.  It was allowing the #4 cylinder to run leaner than all the others.  After that was fixed and everything back together, the #4 temp only got up to 400 with the cowl flaps closed at 75% power at 2000'.

 

[Guest]

3 hours ago, markejackson02 said:

Updating the thread after my last annual.  Boyd took apart the standby vacuum system.  The check value was all gummed up and not working.  It was allowing the #4 cylinder to run leaner than all the others.  After that was fixed and everything back together, the #4 temp only got up to 400 with the cowl flaps closed at 75% power at 2000'.

 

Precise Flight SVS systems have several recurring AD's to be carried out during Annual inspection.  You can find them on the FAA site.

Clarence

[N601RX]

On June 9, 2014 at 7:42 PM, markejackson02 said:

 

 

Although not related, the picture shows a dented fuel supply line on the rear cylinder as well as what looks like aluminum Adel clamps.  These are covered by an AD that do not allow any dents and the Lycoming part number clamp is steel.