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Normal CHTs - should I stop worrying?

JackinMichigan

Well Known Member
I've got just under 10 hours in my RV-10 as of yesterday, and since the first flight I've been fighting a battle with high CHTs. After much work this weekend sealing every leak and removing every flow obstacle, these are my CHT numbers; better than before but still widely varying. This is at level cruise, 24" MP and 2400 RPM, full rich mixture with break-in mineral oil, speed approx. 170 MPH, outside temp mid-30s F:

Cyl 1 - 335
Cyl 2 - 335
Cyl 3 - 315
Cyl 4 - 320
Cyl 5 - 364
Cyl 6 - 347

The numbers are all under my 380 limit, but #5 is way hotter. In fact my coolest and hottest cylinders are right next to each other. I want to think there's something that can be done about that.

Should I just stop fretting and call these numbers good? That #5 cylinder does creep up to 410 or so during climbout, so I'm not sure if I need to get more creative with my baffle layouts or just accept these numbers as normal. I'm curious what these numbers will look like on a 90 degree summer day.
 
Jack, nothing wrong with those numbers.

#5 will need a bypass duct to get it even with the others. Same as the old "washer trick", only better, allows airflow through the top rear fins and feeds air to the lower fins inboard of the intake flange. Lots of info in the archives.
 
The advice I?ve always followed from old time mechanics (& shops) is to run an engine hard & hot during break in, between 380 & 400, to insure the rings seat and not glaze the cylinders. Lycoming red line is 500, I set a 450 no go limit, so even with 400 is well below any thing serious.
With slippery RV airframes this is hard to do so I leave all gear fairings off during break in, try to make the engine work as hard as is sensible.
Your running mid to low 350 temps seem conservative for a 10hr break in engine.
 
Yes, I've heard that you're to run a new engine 'hard', but I haven't heard 'hot'. I've read that for the first 25 hours at least you should keep the power setting to 75%+ as much as possible at full rich, which is what I've been doing, but even with the leg farings off this thing is FAST. The structural speed limit of the RV-10 is around 178mph, and I find my self hitting 170mph in level flight rather easily.

I've also heard that using break-in mineral oil will cause the engine to run hotter than normal, but still the maximum temperatures do apply (it's a metallurgical thing).

If the temperatures I'm observing stay where they are when the outside temperature is 50 degrees warmer then I'm probably OK, but it would still be nice if I could get them all to even out a bit more.

I think I have something like 18 temperature probes all around the plane. The amount of info being thrown at me is rather overwhelming. Never had to worry about half of this stuff in my old 172.
 
Yes, I've heard that you're to run a new engine 'hard', but I haven't heard 'hot'. I've read that for the first 25 hours at least you should keep the power setting to 75%+ as much as possible at full rich, which is what I've been doing, but even with the leg farings off this thing is FAST. The structural speed limit of the RV-10 is around 178mph, and I find my self hitting 170mph in level flight rather easily.

I've also heard that using break-in mineral oil will cause the engine to run hotter than normal, but still the maximum temperatures do apply (it's a metallurgical thing).

If the temperatures I'm observing stay where they are when the outside temperature is 50 degrees warmer then I'm probably OK, but it would still be nice if I could get them all to even out a bit more.

I think I have something like 18 temperature probes all around the plane. The amount of info being thrown at me is rather overwhelming. Never had to worry about half of this stuff in my old 172.

Just curious -- are you seeing 170mph IAS or TAS, at what altitude, and have you verified the indications with a GPS calibration run?
 
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RV?10 Performance
General InfoSpecificationsPerformance



Speed and ranges in statute mph.

*235 hp performance estimated.
Speeds and ranges in statute mph (sm)
Light Weight 2200 lbs * 235 hp 260 hp
Speed
Top Speed 204 mph 211 mph
Cruise [75% @ 8000 ft] 194 mph 201 mph
Cruise [55% @ 8000 ft] 174 mph 180 mph
Stall Speed 57 mph 57 mph
Ground Performance
Takeoff Distance 415 ft 360 ft
Landing Distance 500 ft 525 ft
Climb/Ceiling
Rate of Climb 1,669 fpm 1,950 fpm
Ceiling (est) 20,538 ft 24,000 ft
---------------------------------------------------------------------------------

Gross Weight 2700 lbs * 235 hp 260 hp
Empty Weight 1,585 lbs 1,600 lbs
Speed
Top Speed 201 mph 208 mph
Cruise [75% @ 8000 ft] 190 mph 197 mph
Cruise [55% @ 8000 ft] 170 mph 176 mph
Stall Speed 63 mph 63 mph
 
RV–10 Performance
General InfoSpecificationsPerformance



Speed and ranges in statute mph.

*235 hp performance estimated.
Speeds and ranges in statute mph (sm)
Light Weight 2200 lbs * 235 hp 260 hp
Speed
Top Speed 204 mph 211 mph
Cruise [75% @ 8000 ft] 194 mph 201 mph
Cruise [55% @ 8000 ft] 174 mph 180 mph
Stall Speed 57 mph 57 mph
Ground Performance
Takeoff Distance 415 ft 360 ft
Landing Distance 500 ft 525 ft
Climb/Ceiling
Rate of Climb 1,669 fpm 1,950 fpm
Ceiling (est) 20,538 ft 24,000 ft
---------------------------------------------------------------------------------

Gross Weight 2700 lbs * 235 hp 260 hp
Empty Weight 1,585 lbs 1,600 lbs
Speed
Top Speed 201 mph 208 mph
Cruise [75% @ 8000 ft] 190 mph 197 mph
Cruise [55% @ 8000 ft] 170 mph 176 mph
Stall Speed 63 mph 63 mph

Sigh, I know the specs - I built and fly an RV-10 after all. My question was specific to the OP's performance as his cruise speeds seems a bit fast to me for not having the gear fairings and wheel pants on, not the general performance specs for the model.
 
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The 178mph speed I was referring to is the maneuvering speed, or structural speed, not the top speed. And in Michigan, particularly in the early Spring, the turbulence is such that you should probably stay under that.

The altitude was around 4,000 ft. I did the four-compass-direction IAS calibration and compared it to ground speed, but I keep forgetting to take the numbers home and figure out where my calibration stands. So no, my IAS is not yet calibrated. I might be flying slower than I think.
 
Having 50 hours on my -10 with a fresh engine, I have seen a good drop in the CHTs since it first started flying. I would not worry. Keep flying and see what the temps are 40 hours from now.
 
Not a 540 (or cooling) expert, but my only concern is, as you mentioned, that if you are reaching 410 on climbout when OAT's are in the mid 30's, what will they be this summer when OAT's may be in the 80's or higher on climbout? Maybe not worth worrying about until it is further broken in, but they will certainly get higher as the days get hotter. In general, my CHT's tend to rise just about the same amount as the OAT (ie, if OAT goes up 40 degrees, so do CHTs).

Chris
 
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What you are seeing is perfectly normal for an engine with only the few hours you have on it. Do as Dan describes and fix the rear baffle behind #5 and it will come down. Adjust the front air dams as required. You won?t see much of a significant drop until you have 40 plus hours on the engine and replace the mineral oil.
I wish mine were as cool as yours when I was doing my first flights.
 
The advice I’ve always followed from old time mechanics (& shops) is to run an engine hard & hot during break in, between 380 & 400, to insure the rings seat and not glaze the cylinders. Lycoming red line is 500, I set a 450 no go limit, so even with 400 is well below any thing serious.
With slippery RV airframes this is hard to do so I leave all gear fairings off during break in, try to make the engine work as hard as is sensible.
Your running mid to low 350 temps seem conservative for a 10hr break in engine.

Dangerous advice. Definitely good to run them hard at break in to seat the rings, but not hot. I accidentally let my CHT's get into the mid-400's' for half a minute during the first hour and the cylinders glazed. The fresh cylinders are more susceptible to glazing before the rings seat and glazing is caused by heat. The material deposited (i.e. the "glaze") is coked oil.

Larry
 
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