How fast do your CHTs rise?

[SwimmingDragonfly96]

7A, O360-A1A, carb w/ big jet, CS prop.

Things are a lot better than they were, but I still get really hot, really fast. There's a certain portion of takeoff, pretty much right when I take off, I will bust 420 pretty regularly, especially in this heat. Two flights ago, hit 441, but didn't even notice until I downloaded my savvy data. If I nose down, temps come down immediately, and they typically stay there the rest of the flight, regardless of climbs, etc.

I have retarded my timing to 23 BTDC, enriched the idle mixture, did some moderate work on the baffling, and it all made a significant difference to bring down my CHTs. Now that it's super hot at my home base in KSEE, I'm creeping into too hot territory again, even if it's a blip (12s at 441). Fuel flow is about 17GPH when the CHTs peak after takeoff.

I'm not asking for troubleshooting help here, as I'm going to redo my seals very soon, however, is it normal for the temps to go up as fast as they do on my plane? I read of some people getting hot 1000' or 2000' feet in, I'm super hot 100' above the runway.

 

[blaplante]

Chasing some issues on a 7A at F70 earlier this year, it looked like the peak CHT was happening well before turning crosswind. Some of that was due to deliberately speeding up to 90-100 mph once airborne.

Your profile says San Fran, but you are based at KSEE?

 

[Carlos151]

At about the 09:45 mark you get a big spike on your fuel flow. Is that your takeoff power application? CHT's are already pushing 400 if that's the case. Doesn't look like you're getting a full rich mixture on your takeoff and initial climb out. Getting CHT's that high and that quick does not look normal. Mixture not full rich? Fuel line blockage? Oil cooler blocked? Big leak in your baffles? Even later, a 370 CHT with 14 GPH FF seems high. What speed are you climbing out at?
Here in middle TN temperatures have been in the mid 90's. CHT's with my IO360 CS prop typically don't get hotter than 375 climbing out at 25 square, 120 knots and slowly leaning during climb out.

 

[SwimmingDragonfly96]

At about the 09:45 mark you get a big spike on your fuel flow. Is that your takeoff power application? CHT's are already pushing 400 if that's the case. Doesn't look like you're getting a full rich mixture on your takeoff and initial climb out. Getting CHT's that high and that quick does not look normal. Mixture not full rich? Fuel line blockage? Oil cooler blocked? Big leak in your baffles? Even later, a 370 CHT with 14 GPH FF seems high. What speed are you climbing out at?
Here in middle TN temperatures have been in the mid 90's. CHT's with my IO360 CS prop typically don't get hotter than 375 climbing out at 25 square, 120 knots and slowly leaning during climb out.

Hey Carlos. The day of that flight, it was 98F on the field and a long taxi to the runway, so my CHTs were approaching 400 on the ground. Spike in fuel flow is when I took off. From my understanding 17 GPH should be solid for my set up? According to savvy I’m a bit higher than average for my set up.

 

[ronrapp]

I have flown all the 2 seat RVs except the 14 and most of them seem to run with higher CHTs than you'd get with the typical certificated aircraft. I watched the previous owner of my plane go through the baffling, fuel flow, instrumentation, and more in search of any ways to improve. The airplane had been based at a high altitude airport and the fuel system was set up for that environment.

Anyway, in summertime, I'll climb at 120+ knots indicated and the CHTs often approach but don't typically exceed 400 degrees. I usually peak shortly after leaving the pattern and then the CHTs decline. I find the best results by running lean of peak. I'll even climb LOP.

I should note that I have high compression cylinders. IO-360 / 195 hp / fixed pitch.

When I was at the West Coast Formation Clinic, it was quite hot but I just left the mixture full rich for every flight and didn't have any issues. If I was you I'd check the baffling closely. I recall Mike Busch saying that a hole the size off a quarter would rob you of nearly half your cooling airflow. Pretty dramatic.

For comparison, here's a recent flight I made. Note my max fuel flow is like 3 gph less than yours but my CHTs stay way lower. This is out of Corona (AJO), so a relatively similar environment:

https://apps.savvyaviation.com/flights/shared/flight/7204921/8bcf2115-5a9f-4b8d-ba98-a8201869d85a

--Ron

 

[Draker]

During these hot summer days, I regularly blow through 400° on takeoff. My ability to stay below that really seems to depend on the outside temperature. On cooler mornings, I'm able to (just barely) keep it below 400°, but when it's over 35°C (over 95°F) out, there's simply no way to both stay cool and climb at a safe rate. I've tried some of the mitigations you mentioned, no dice so far.

Currently, until I figure this out, I fly with a CHT yellow-line of 400°F and a "soft" red-line of 425°F. My takeoff routine this summer has been: When I exceed 400°, I throttle back, reduce RPM to 2500, and pitch for >100KIAS. If I reach 425°, I consider it a mini-emergency, and completely stop my climb and speed up for airflow if I can do so safely. Fortunately, once I'm at altitude and cruising, my temps are always fine.

As an RV newbie, always having to keep an eye on CHTs during takeoff is both worrying and irritating. I've heard from other RV flyers who never even approach 400, so I know it's possible. Very frustrating. I feel your pain, brother.

 

[gasman]

My oil cooler is controlled with a 3" butterfly valve. In the past I have always had hot cyl's during climb out in OA temps over 90 deg.

This year (hot season) I tried something different... I closed the oil cooler's manual valve and let that air go to the heads. It worked!!! The air was not needed for the oil during the first few minutes of the climb because the oil does not heat up as quickly as the heads.

During my run up, I close the oil butterfly valve and open it when I get a High Oil Temp warning on my MGL at 200*. By then I am at about 4K feet and I open the valve and the oil settles down to about 185-90 and the cyl heads never broke 390*

The Question was asked in another post "Do you need to control air flow to the oil cooler"..... For me the answer is YES because I use (need) the extra airflow to cool the heads during hot weather during climb out.

 

[SwimmingDragonfly96]

Chasing some issues on a 7A at F70 earlier this year, it looked like the peak CHT was happening well before turning crosswind. Some of that was due to deliberately speeding up to 90-100 mph once airborne.

Your profile says San Fran, but you are based at KSEE?

Did you chase down the issue? Recently moved the plane down to Santee, currently live in SF and work in SD but SD permanently soon.

 

[DanH]

When considering temperatures reported by other folks, always note cylinder type. As a general rule, the parallel valve engines consistently show higher CHT and lower oil temperature, while the angle valve engines will show lower CHT and higher oil temperature.

Also be aware of reality regarding available dynamic pressure. The typical RV cannot maintain Vx or Vy for an extended period of time. When it's hot, speed up. Dynamic pressure is a function of velocity squared, so available pressure nearly doubles by changing from 90 knots to 125 knots.

Adjunct to the above, propeller and inlet choices can have a large effect on climb cooling. A prop with a good airfoil choice near the root, coupled with inlets capable of efficiently capturing the propeller's outflow, can have a profound effect on climb cooling. The propeller outflow is a source of high velocity air.
.

 

[lr172]

IMHO, the question is not how fast they rise, but how high they rise. I left my cowl plugs in once and CHTs were at 405 long before I hit pattern altitude and that was winter, so yes they rise fast when the air is not flowing well. The issue is not the speed of rise, but the point they are rising to. If you are getting to 440 early in the climb, something is wrong. There are hundreds of RVs out there that can easily climb and stay under 400. The fact that all is fine when level, tells me you have airflow issues under the cowl somewhere. You really need someone with experience in this area to take a look at your setup and offer some advice. You said not looking for help addressing so none offered.

As I look at your charts, I see that you are already at 375* BEFORE take off. That is insanely high for idle and taxi operations. On the hottest days, my planes are under 300 on the ground. I will reiterate that you need some expert guidance to help with your cooling airflow and sealing arrangement.

Larry

 

[PilotjohnS]

Inlet ramps

I had high chts on #3 during phase 1. I discovered the inlet ramp was too close to the #1 cylinder and restricting the air flow.

I need to climb out at 100 kts to keep below 400 cht.

 

[blaplante]

Did you chase down the issue? Recently moved the plane down to Santee, currently live in SF and work in SD but SD permanently soon.

We made lots of little changes than made lots of small improvements. Plane is a O-360 180HP with Catto 2 blade FP prop. In the end we just raised the white flag and went with...
https://store.vansaircraft.com/rv-6-6a-7-7a-9-9a-cowl-louver-kit-cowl-louver-kit.html
Not a 100% solution, but a significant improvement.

Of note, I'm at L18, and my 6A with O-320-H2AD and two blade Catto doesn't have major CHT problems. Hot summer days I have to watch it and treat it appropriately but it isn't nearly as bad as yours or that 7A I was working on.

I did spend the effort to get a cowl exit ramp installed on one side of my 6A (similar to what the 8 has, a lower firewall bulge). I do think this helps.

 

[SwimmingDragonfly96]

IMHO, the question is not how fast they rise, but how high they rise. I left my cowl plugs in once and CHTs were at 405 long before I hit pattern altitude and that was winter, so yes they rise fast when the air is not flowing well. The issue is not the speed of rise, but the point they are rising to. If you are getting to 440 early in the climb, something is wrong. There are hundreds of RVs out there that can easily climb and stay under 400. The fact that all is fine when level, tells me you have airflow issues under the cowl somewhere. You really need someone with experience in this area to take a look at your setup and offer some advice. You said not looking for help addressing so none offered.

As I look at your charts, I see that you are already at 375* BEFORE take off. That is insanely high for idle and taxi operations. On the hottest days, my planes are under 300 on the ground. I will reiterate that you need some expert guidance to help with your cooling airflow and sealing arrangement.

Larry

Hey Larry,

I actually did take it to a more or less dedicated RV mechanic and he tweaked the things I mentioned above and got me into manageable territory for the not crazy hot times. During these hot summer months, I am regularly pushing 400 before takeoff.

My seals have lots of leaks, hence they will be replaced shortly. Hoping for an improvement after that.

 

[Dugaru]

Same here

I have had precisely the same experience. My hot cylinder was #2, same side as the oil cooler. I discovered that closing the shutter on the oil cooler keeps CHTs well within limits. And like you I have found that oil temps don't get hot nearly as quickly as CHTs, so it's easy enough to wait to open the shutter at altitude.

It's possible that further tweaking with baffling etc. could get #2 down, but for now the oil cooler trick has completely solved the problem.

Incidentally, Mike Busch says that for Lycoming cylinders, think of the green arc as going to 400, and the yellow arc going to 420. That makes sense to me, and seems conservative compared to Lycoming's own numbers. I used to be super worried about exceeding 380 but I now think that was being overly cautious. I'm aware of zero data suggesting any difference in cylinder longevity etc. between running at 380 and running at say 400. My various cylinder-wear issues over the years have never correlated to the cylinders running the hottest.

My oil cooler is controlled with a 3" butterfly valve. In the past I have always had hot cyl's during climb out in OA temps over 90 deg.

This year (hot season) I tried something different... I closed the oil cooler's manual valve and let that air go to the heads. It worked!!! The air was not needed for the oil during the first few minutes of the climb because the oil does not heat up as quickly as the heads.

During my run up, I close the oil butterfly valve and open it when I get a High Oil Temp warning on my MGL at 200*. By then I am at about 4K feet and I open the valve and the oil settles down to about 185-90 and the cyl heads never broke 390*

The Question was asked in another post "Do you need to control air flow to the oil cooler"..... For me the answer is YES because I use (need) the extra airflow to cool the heads during hot weather during climb out.

 

[D-Dubya]

What Larry Said...

I agree with what Larry said on Post #10. The rate of CHT rise after the application of take-off power seems reasonable. But the starting temperature on the ground seems way too high to me, indicating that something is amiss.

For reference, I have a parallel valve IO-360 with a plenum and a Sam James cowl, and my CHTs after a run-up are almost always below 300 degrees F. On a hot day, the CHTs may go to the 380's on the initial climb, but they start dropping back down after the power is reduced to a cruise-climb setting of 25" and 2500 RPM. If I'm doing pattern work and the engine is staying hot, the temps will bump against 400 in the initial climb on a hot day.

So yeah, absolutely look at the seals & baffles and anything else that may be affecting cooling flow into or out of the cowling. Something is causing you problems. If your RV friend doesn't find a smoking gun, find another set of eyes to help you chase this down.

 

[Draker]

Oh, and to answer SwimmingDragonfly96's original question: How quickly do CHTs rise? I think I’m in the same boat as you.

For me, the WORST case I've seen within the past month was reaching 400°F during my ground roll. This was a very hot day. Airspeed target was 110KIAS (Vy+23). Red line in the top plot is MAP. Click plot for clearer view:

• OAT on the ground: 93.5°F
• Hottest CHT while idling on the ground: 377°F
• At ~250ft AGL, CHT1 reaches 415°F, I throttle back very slightly
• At ~1100ft AGL, CHT1 reaches 421°F, I'm at a safe altitude so throttle back significantly, which arrests CHT growth

Here is a cooler day. Airspeed target 110KIAS:

• OAT on the ground: 76.5°F
• Hottest CHT while idling on the ground: 325°F
• Throttle back to 24"MP at ~400ft AGL to arrest CHT growth

Yes, I know it is a bad habit to throttle back during the climb while below a safe altitude.

 

[mfleming]

7A, O360-A1A, carb w/ big jet, CS prop.

Things are a lot better than they were, but I still get really hot, really fast. There's a certain portion of takeoff, pretty much right when I take off, I will bust 420 pretty regularly, especially in this heat. Two flights ago, hit 441, but didn't even notice until I downloaded my savvy data. If I nose down, temps come down immediately, and they typically stay there the rest of the flight, regardless of climbs, etc.

I have retarded my timing to 23 BTDC, enriched the idle mixture, did some moderate work on the baffling, and it all made a significant difference to bring down my CHTs. Now that it's super hot at my home base in KSEE, I'm creeping into too hot territory again, even if it's a blip (12s at 441). Fuel flow is about 17GPH when the CHTs peak after takeoff.

I'm not asking for troubleshooting help here, as I'm going to redo my seals very soon, however, is it normal for the temps to go up as fast as they do on my plane? I read of some people getting hot 1000' or 2000' feet in, I'm super hot 100' above the runway.

My data log looks like yours.
At first I had trouble keeping the #1 cylinder temp down then I fixed an air leak and now it trends with the others, although #1 & #4 are my two hottest.

On a cool morning, like today, my CHTs are all below 400°F during a fast climb out. On a hot day, no way. For example, I stopped to get fuel, started up and had a long taxi. By the time I was adding power, my hottest cylinder was at 400°F. That flight had a high of 450°F...bummer. I've checked for baffle leaks multiple times and plugged every gap I could see.. Very frustrating.

I haven't tried taping off some of the oil cooler (my oil temps are low...168°F) but I might do that next.

But to answer you question directly, yea, my temps jump up fast on takeoff.

PS: I try to get to 120kts as soon as I can.

I would be interested in finding a RV cooling guru in the PNW to help me troubleshoot.

 

[RV8JD]

I would be interested in finding a RV cooling guru in the PNW to help me troubleshoot.

Scott M ('rvbuilder2002') ?

https://vansairforce.net/community/member.php?u=1835

 

[mfleming]

Scott M ('rvbuilder2002') ?

https://vansairforce.net/community/member.php?u=1835

Thanks! Yeah, Scott would be great! Just sent him a PM.

 

[Draker]

I'd also be willing to fly up from NorCal for some kind of an expert-run "cooling clinic".

 

[lr172]

Hey Larry,

I actually did take it to a more or less dedicated RV mechanic and he tweaked the things I mentioned above and got me into manageable territory for the not crazy hot times. During these hot summer months, I am regularly pushing 400 before takeoff.

My seals have lots of leaks, hence they will be replaced shortly. Hoping for an improvement after that.

You are welcome to call and I can walk you through the 10-15 things to look for. A lot of the stuff is not obvious like a poor air cleaner box seal that sends ram air pressure into the lower cowl. I helped a guy with a problem like this. I think he said afterwards that CHTs were down 40* I have seen a few that left out the rubber seals (or put then UNDER the ramps to make cowl removal easier) at the cowling inlets and they need two cowl flaps to keep the heat under 430 during climb. Sorry, but I don't put all mechanics into the expert category.

Larry

 

[dbaflyer]

also use the oil cooler shutter

I am in the same camp as Gasman.

I close the oil cooler shutter on takeoff and open as needed as the temp starts to climb over 200.

My #4 is the hottest and with the cooler open I quickly rise to 420 - 425, but with it closed stay around 405.

This is an O-320 with 1 mag and 1 electronic ignition coil pack

 

[PilotjohnS]

Thank you for posting

Thank you for starting this thread.

I was waiting till my oil temp reached 100F before takeoff, namely to make sure all the vapor was out of the fuel lines. But this meant my CHTs always went above 400.

After reading this thread, I realize CHTs are more important to monitor for my engine. So take off now is as soon as practical to keep CHTs low, with oil above 85F. This works well by allowing rapid climb after takeoff before pushing over and doing cruise climb to manage CHTs,

 

[Mikeyb]

My RV8 cooling

DanH mentioned the prop outflow. I have the big Hartzell composite. My baffles are good but not exceptional. It never gets hot. Hottest temperature ever recorded was 390. The measured accuracy is +/-15F.

Trouble is I don’t think I’ve ever flown it over 85F OAT. To first order it’s linear and my temps on this 70 deg morning would be 25 degrees higher compared to 95F data.

Data in pics below was a flight aug 8. 70F OAT. Corrected to 95F my temps would be

Taxi/Takeoff 295
Climb WFO 300 MSL to 4300 @95 MPH (2minutes 30 s seconds from throttle up) 395
Lazy 8’s at 24x24 ROP 365
Taxi and Shutdown 295

 

[Taltruda]

Just a data point, my carbureted, parallel valve O-360 in my -4 runs cool.. in Vegas, I can often keep CHTs high 200s, maybe tickling 300 before takeoff. I limit my runup to only a few seconds, I face the plane onto the wind whenever I can, I taxi pretty much at idle, perhaps 750 at most, I lean the mixture to max RPM rise on the ground.. I have nice baffles around the engine, air filter inlet, and cooling ramps. My takeoff procedure is to accelerate in ground effect to the end of the runway to maximize airspeed, then climb out at 110 knots. Fuel flow is 16GPH. I don’t start leaning until ~5,000 msl, and then only to maintain takeoff EGT. On the hottest Last Vegas days, I have CHTs max about 385, then settle around 365 in cruise. Oil temps might get to 210 in a long climb to altitude, but cool down to 190 in cruise.