Hot Cylinder Temps--What's Going On?

I am troubled with high cylinder temps on my initial flight of the day. My equipment: RV-6, O-360, 1,000 hrs, Lasar ignition/Slick Mags, VM-1000 monitor.

Usually on my first climb out, my temps climb to about 430 deg, then level off and drop when leveling out. I can do a touch and go and the temps only climb to about 375. Normal cruise is about 360.

I replaced the intake gaskets and checked for induction leaks and rebuilt the baffle seals. Fuel flow on initial climb is about 17-18 gph. I turned off the Lasar system on one test flight with no change. Mags were recently inspected and are fine.

All cylinders run about the same temps with 2 and 4 slightly higher. Both cyl and EGT temps are quite uniform in cruise. All four cylinders are monitored so I doubt it is a probe problem. The Lasar monitors cyl temps and the probe checked out OK.

Oil temp is fine and I can keep it below 200 even on the hottest days.
Anyone have any ideas? Does the Lasar system "run" the temps up initially? Looking for answers, and thanks in anticipation.

Mark

heat soak

What are your CHT's prior to T/O? I was troubled by this for my entire first year and worked really hard to seal things up (several threads on High CHT's). In the end, everything I did helped reduce climb and cruise CHTs significantly but if the temps are already high on take-off due to long taxi or holding for traffic CHTs will climb into the 400's sometimes in the 420 range. What I believe is important is shortly after take-off after you've gained A/S the temps should begin to fall quickly - mine do. If I take-off with CHT's less than 370 they never go above 400 in a normal climb (130mph).

Not an expert but I have heard a similar story and it proved to be wrong timing setup. Checking the timing is a good idea anyway.

To me it seems RV's are not limited by climb performance due to HP/prop/etc., they are limited in climb performance by CHT's at least mine is. My #1 & #3 with #3 leading the pack is always my climb limitation.

Most of the time I don't have an issue solo with some fuel burned off but load her up dual with full fuel and I have to watch it. 400?-410? is my max climb temp, if it starts to go higher, I put the nose down and just wait. While I don't like to, I have seen 420? on #3 when trying to climb over a ridge or something after takeoff to stay on course.

In cruise all are bellow 350?.

Just to add to the good comments already made, if the OAT was 25F warmer than your last flight CHT's will run 25F warmer also.

Brantel said:

To me it seems RV's are not limited by climb performance due to HP/prop/etc., they are limited in climb performance by CHT's at least mine is.

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Mine too. I've been fighting high CHT's like many and have been going through all the steps like everybody else. I've seen some improvements but nothing major. Still working on it.

If you have a FP IO-360 RV that can climb at Vy to 4000ft on an 80 degree day with CHTs under 400, I'd love to see it.

I'm not saying I need to climb at Vy, but there are times it be nice.

One question i sometimes ask that hasn't been mentioned is "what are using for climb speed?" Too many folks climb the RV's too slowly. At least for my -8, I found during Phase 1 that best rate of climb was fairly flat over a broad speed range, maximizing about 105 knots IAS at Sea Level. Climbing at 120 changes it very little. Climbing down at 90 KIAS is a great way to heat up the engine, and doesn't get me any higher any faster.

Paul

boom3 said:

If you have a FP IO-360 RV that can climb at Vy to 4000ft on an 80 degree day with CHTs under 400, I'd love to see it.

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Hmmm.....will a CS IO-390 do it for you?

http://www.vansairforce.com/community/showpost.php?p=515300&postcount=44

Have LASAR - No Problem

Initially the new engine delivered by Lycoming (O-360-A1A) drop ship ordered through Van's with LASAR ignition system with test cell data blah, blah, blah. The timing was so far off it was amazing that it could run at all - I had to throttle way back to get the ECT off the peg even in level flight. I had no CHT monitor at that time. I bought the LASAR timing box and set the timing correctly and there have been no problems with the system since then. I have since installed probes in all 4 exhaust pipes and all 4 cylinder heads along with EI CHT and EGT instruments. I throttle back to 2500 rpm or so for climb noise (good neighbor), 2450 rpm for travel cruise and 2720 rpm for racing. CHTs range from 300 (cyl #1) to the 330's for the others. I lean the EGTs on the rich side of peak at 1300 or slightly less for the highest temperature cylinder (Cyl #4). I have a lot of custom baffling in the lower cowl so your numbers will be different than mine but I feel confident that the only possible connection the LASAR system would have is if the timing is not correct. The special LASAR timing box is expensive and the instructions are easy to misinterpret (the first time I tried to use it I came up with precisely the same setting as came from Lycoming which was approximately 65 degrees off of the proper setting) but it is essential for setting the timing of the LASAR system.

Bob Axsom

Ironflight said:

One question i sometimes ask that hasn't been mentioned is "what are using for climb speed?" Too many folks climb the RV's too slowly. At least for my -8, I found during Phase 1 that best rate of climb was fairly flat over a broad speed range, maximizing about 105 knots IAS at Sea Level. Climbing at 120 changes it very little. Climbing down at 90 KIAS is a great way to heat up the engine, and doesn't get me any higher any faster.

Paul

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I agree totally.

I typically climb at 120 knots which lets the fixed pitch prop wind up to 2500 rpm, cooling is great, plus I can see over the nose. Climbing at 90 mandates S turns as straight ahead is a blind spot, at least for me.

Paul

You are right. Although my Vy is 95KIAS, I can climb at 110 to 120 and only lose 200 or so FPM. Although this does help, I can still get to 400 (CHTs) pretty easily on an 80deg day.

Dan

I should have worded that a little better. I meant, bring it over, I'd love to see it. Your airplane and results are awesome! What I wouldn't give to be your neighbor.

I'm guess what I'm saying is, I'm just regular guy that built the best airplane I could with what Van's gave me to work with. Perfect? Not even. Room for improvment? Definately. I've done all the normal stuff. Smooth the inlets, close one side of each eyebrow, verify good baffle seals, confirm good sealing on lower inter cylinder baffling, open up exit area a little (A model), etc. Various experienced RV builders along with A&P's agree it all looks pretty good.
I guess I'm just suprised at the wide spread of heating results with the same plane, same cowl, same baffling, and same engine. Some people have no problems, (Didn't do anything special) while hundreds of others have to fight it for what seems like years.

I second exactly what Jeff said. I sure wish Dan was here in my area to tell me how to fix mine!!!

Might have to take a day trip to see the "Cooling Doctor"....

Paul,

Yes I can lower the temps a little by climbing faster than my normal 120 mph. We fly a lot of formation and matching my speed with others can be some of the cause as well as not climbing with WOT for extra fuel cooling.

Bob,

I have access to the Lasar timing box and checked timing just recently. FWIW, Lasar maintains you need to use fresh batteries each time you use their box.

Dan,

08A-KFFC--101 NM...ha.

Mark

strahler13 said:

I am troubled with high cylinder temps on my initial flight of the day......Usually on my first climb out, my temps climb to about 430 deg, then level off and drop when leveling out. I can do a touch and go and the temps only climb to about 375. Normal cruise is about 360.

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Mark, yours is an interesting problem (first climb of the day only).

Are you sure you're comparing apples to apples? By that I mean do you hit 430F by pattern altitude on that initial climb of the day? Put another way, if the "go" in "touch and go" became a continued climb to some cruise altitude, would the temps eventually hit 430?

DanH said:

Mark, yours is an interesting problem (first climb of the day only).

Are you sure you're comparing apples to apples? By that I mean do you hit 430F by pattern altitude on that initial climb of the day? Put another way, if the "go" in "touch and go" became a continued climb to some cruise altitude, would the temps eventually hit 430?

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Sunday I climbed to 3500 ft (2,700 AGL) and hit 430 deg. Then straight and level for a few minutes until temps came down. Then into the pattern for a touch and go. On the TNG departure, I kept the same power and speed settings and the temps only climbed to about 385--with a "warm" engine. This is what baffles me.

Mark

Oil issue?

Having not spent any time in my professional life with GA engines..

What your problem sounds like to me is a sticky thermal valve to the oil cooler. The oil in the engine may be up to the green but is the valve opening fully to the oil cooler at the right time?

My suggestion is to watch your oil temp/pressure on the first flight and on the TNG to see if it varies more than the given 25-50 degree range your CHT's give.

I sure wish Dan was here in my area to tell me how to fix mine!!!.

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Jeff, Brian, if you walk around fly-ins with me as we talk to owners, you'll see me looking and feeling up inside cowls to check the fit of the baffle rubber. I've never met an owner with really, really nice rubber fit who also complained of high CHT. It is not the whole picture, but it is an indicator; you can bet the baffle tin was fitted and sealed, with everything just so.

The norm is conventional GA baffling tin, which is rarely tight or sealed. We're used to seeing it that way, and hey, it works fine on your Cherokee. Your A&P or local Old Crow looks at the same fit on your RV and declares it fine and dandy. What gets forgotten is that the Cherokee example is flowing vast quantities of mass through the cowl to make it work, while our tight little Vans cowls were designed with an eye toward minimizing cooling drag. The RV cowl just doesn't flow as much air, thus we must get maximum heat transfer to the air we do flow. We cannot afford leaks; every molecule must carry away heat.

If I were a cooling doctor I would, like your medical doctor, insert a thermometer in your exit as a very early diagnosis step. I'd be looking for high temperature cooling air.....or to be more precise, I'd want
(exit temp - OAT) / (CHT- OAT) to be 0.3 or higher. The 0.3 figure is not carved in stone (I'm still learning), but it's not far off. For sure higher is a good thing.

DanH said:

If I were a cooling doctor I would, like your medical doctor, insert a thermometer in your exit as a very early diagnosis step.

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OH NO

Visions of potatoes ------- make them go away AGGGGGGGG

DanH said:

Hmmm.....will a CS IO-390 do it for you?

http://www.vansairforce.com/community/showpost.php?p=515300&postcount=44

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I also have no problem with cylinder temp at best rate from sea level to any height I like, I?ve done best rate to 15,500? in the hot summer desert many times with no issues, CHTs below 320. One note, my IO-360 A1A and Dan?s IO-390 have angle valve cylinders and oil squirting in the bottom of the pistons, these differences probably contribute to lower CHTs so it?s not exactly apples to apples.

Russ McCutcheon said:

One note, my IO-360 A1A and Dan?s IO-390 have angle valve cylinders ------

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Good point, I would be interested in looking at a parallel head, and an angle one side by side.

I suspect that due to the splaying of the valves, there is a lot more cooling fin area between the valve pockets.

Remember the issue of casting flash in this area, and the dramatic difference in CHT it made for those who cleaned it out???

Also, stop and consider where the CHT probe is located.

Wonder if any of the folks who are having temp problems are using a ring style sensor under the plug.

strahler13 said:

Sunday I climbed to 3500 ft (2,700 AGL) and hit 430 deg. Then straight and level for a few minutes until temps came down. Then into the pattern for a touch and go. On the TNG departure, I kept the same power and speed settings and the temps only climbed to about 385--with a "warm" engine.

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Did you have the same beginning CHT on the runway in both cases (CHTs probably fell further during the power-off descent), and did you climb to 3500 after the T&G?

DanH said:

We cannot afford leaks; every molecule must carry away heat.

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Our intuition tell us this must be true..but alas there is more going on here than merely plugging leaks. As a quick sanity check I completely sealed my oil-cooler inlet , a 3" diameter leak as well as the inlet to the heater muff, a 2" diameter leak, plus both mag blast tubes 2x1" diameter leaks for a total reduction of 11.775 sq in of leakage area and only saw a marginal reduction in CHTs during WOT cruise, full rich (about 5-10 deg on the hottest cyl) under test day conditions. I only did this once and only long enough to witness the overall change. I returned to base when OT began climbing above 200 deg F and re-opened those inlets. sealing leaks is good, but unless yours is truly horrendous to start with I wouldn't expect much from little dabs of RTV here and there.

As I stated in my first post on the subject, the initial temperature of the engine at T/O has as much to do with the CHT's during the climb as the quality of the cooling system, the A/S during climb and OAT.

When I am able to taxi straight from my hangar to the runway and can get the run-up done without any delays and T/O with CHT's below 300 like I did this AM, I never see CHT's higher than 380 in a 130MPH climb to 6000 ft PA with ground OAT of 82. I did the same thing yesterday but had to taxi all the way to the other runway and took off with CHT's at 365. Max CHT was 415 at about 2000ft but was back down to 375 by the time I leveled off at 5500. The cooling system was doing its job very well. When we add t/o power we create a significant amount of heat very quickly yet the airplane isn't moving fast enough to accommodate for the sudden addition of heat and therefore CHTs rise. A better check of the cooling system is if it brings those temps back down as you stabilize in your climb. Testing during the T/O climb is a poor validation of the cooling system unless you control all the variables very carefully between changes in configuration - i've been experimenting with this for nearly a year now.

Paul is spot on - the climb curve is very flat over a wide range of A/S but cooling capacity increases significantly with A/S. I was climbing at 700fpm at 160MIAS, WOT, earlier this afternoon - CHTs were 320-340's. I won't be happy till I get them below 100 though

i was lookin for a similar post on hot chts but this is as good as any to post.

someone had mentioned about taping the front of the cowl seams in the inlet. my chts dropped by 10 degrees F. i was very surprised.

Yeah Ed, that was me. One of the many incremental things I've done to reduce my CHTs but still if the engine is hot at T/O it is always going to get hotter until the airflow can catch up... no getting around it.

DanH said:

Did you have the same beginning CHT on the runway in both cases (CHTs probably fell further during the power-off descent), and did you climb to 3500 after the T&G?

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Dan,

My monitor starts at 300 deg, if i remember correctly, so i dont know where i start on either run. I did climb to 3500 on the TNG. i just find it hard to believe that the temp from start up, short taxi and take off is higher than a TNG when the temps recently were at 430.

Thanks for thinking,

Mark

Russ McCutcheon said:

One note, my IO-360 A1A and Dan?s IO-390 have angle valve cylinders and oil squirting in the bottom of the pistons, these differences probably contribute to lower CHTs so it?s not exactly apples to apples.

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Good point Russ....we have no good way of comparing the heat transfer ability of angle valve and parallel valve cylinder heads, other than perhaps estimating fin area. You're probably right in that the angle valve heads likely have more fin.

That said, engines are engines. Some percentage of combustion energy is simply heating the parts, so more HP equals more cooling requirement. Substitute a 200 or 210 HP engine in place of a 180 and you must increase system cooling capacity. Put another way, my IO-390 generates about 15% more waste heat than an O-360. Given the same cowl (thus the same cooling air mass), the only way to increase capacity is to increase the temperature rise of the mass. That's exactly what additional fin area would do. A parallel valve owner can do the same by making absolutely sure all his fin area is in full contact with cooling mass.

I doubt the oil squirters result in much CHT reduction. All piston contact is with the cylinder barrel at some distance from the head.

RV8R999 said:

Our intuition tell us this must be true..but alas there is more going on here than merely plugging leaks.

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Yep......

turbo said:

someone had mentioned about taping the front of the cowl seams in the inlet. my chts dropped by 10 degrees F. i was very surprised.

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.....although chasing them down is worth the effort.

cylinder metalurgy affect on CHT?

I've seen it suggested that ECI cylinders tend to run hotter than Lycoming. I have an ECI engine, 9:1 pistons and PMags and have been doing similar baffle and climb angle things to reduce CHT's incrementally. I think I'm almost there but I was wondering what the brain trust thought about differences between manufacturers/metallurgy explaining some of the lack of troubles some folks are having vs the CHT issues others are having.

Would a Poll be useful, ie "at 120kt climb on an 80 degree day, do you typically see CHTs over 400 degrees? What engine, compression ratio and ignition do you have"? I have no idea how to set up a poll like that or how to phrase it so it would yield useful data.

Jeremy Constant

oil squirters

interesting point about the oil squirters. I have them in my Xp-360. I've wondered if during the first t/o when OT is typically way below steady-state if the increased viscosity reduces cooling effectiveness? This would be a good test.

Mark,

Lasar ignition systems do have a 5 minute (I think that was the amount) timer on initial power up, which prevents any timing advancement beyond baseline. The idea is to allow time for climb out without extra heat that might result from advanced timings at less than SL MAP's. I don't recall if the timer is reset when doing mag checks, which disables the EI also, or just on initial power up.

However, your issue seems to be the opposite... but, this timer could explain your first flight observation in some way not yet contemplated.

The cht trip point (where baseline timing kicks back in) on the Lasar system might be something fairly high, like 450, but check this. Not relevant, but it was mentioned.

You have not mentioned what power settings and, most importantly, what mixtures you are using during climb out. I can climb on a 90F day from 1k' to 10k' and not see any cht's over 380ish. My oil will climb to around 210, but will fall again after leveling off. On leveling out, my summertime cht's will run in the 310 to 340 range, depending on OAT. This takes some mixture control though. BTW, I'm running injected O360 with dual Lightspeed EI's. I previously had a Lasar system, and it did run hotter than the Lightspeed, no clue why.

On climbs, one can either run WOT and full rich, which will certainly keep things cool, or one can dial back to no more than 24/24 and lean things to LOP, if the engine is balanced in terms of when each cylinder reaches peak egt. (Tons of stuff in these forums about this.) If I were to climb at 24/24 at peak power type of egt settings (say 100 - 150 ROP), I would easily go over 400F on that same climb.

Come on up to MN this winter, you'll not have any cht problems!

Sometimes high CHT can be related directly to fuel flow, or lack of I should say. Everything else can be perfect but if there`s not enough fuel for the HP it will be high CHT. I have a mildly hotted up parallel valve built by a good shop. Servo was the same as on a 180 HP 360 so changed it to one off a 540, get an extra 12 litres at WOT, problem gone. May be check your fuel flow as well.

Regards Peter

Got a look at my notes at home. The 0.3 figure in post # 17 is too low; 0.5 is probably closer when measuring at the cowl exit. I don't know for sure yet.

The above is a measure of heat transfer efficiency, not cooling capacity.

For example, assume two RVs with identical engines at identical power settings, thus the same cooling requirement. Both are flying along with the same CHT. Exit temperature measurements result in 0.3 for one and 0.5 for the other. We can be sure the 0.3 aircraft is slower. Low heat transfer efficiency requires that it flow more cooling mass to get the same CHT.

How might the efficiency figure be used as a diagnosis tool?

Assume a particular installation has a high CHT problem, but also has a high transfer efficiency value. The problem is lack of mass flow. This setup would be a candidate for (1) more exit area, and/or (2) better pressure recovery. (BTW, either will result in more mass flow, but better pressure recovery will lower drag because of higher exit velocity.)

High CHT with a low transfer efficiency would indicate mass is passing through the system without being heated very much. This system needs better baffle work. Adding exit area would the wrong approach; it would indeed lower CHT by increasing mass flow, but unnecessarily slow the aircraft.

Actual measurements are interesting to observe. I've been flying with a temperature probe in the baffle opening under the #1 cylinder; think of it as a single-cylinder data point. Recall my cowl has a swappable/removable exit panel. Removing it completely creates a HUGE cowl exit area. So, two flights, one with a huge exit and another with a very small exit., ie a very large variation in mass flow.

Flight #1, huge exit, large mass, probably higher velocity: probe 135F, CHT 270F, OAT 52F, efficiency 0.38
Flight #2, small exit, low mass, probably less velocity: probe 237F, CHT 320F, OAT 83F, efficiency 0.64

In the huge exit case efficiency dropped because of excess mass flow and likely high velocity through the cylinder fins, which is all quite obvious from the very low CHT. Pressure drop between upper and lower plenum was 17" H2O! CHT only increased 50 degrees with the small exit, even in the presence of higher OAT. Here's the kicker....airspeed was down 18 knots with the huge mass flow.

Here's a picture of what I'm experiencing.
Dynon D120 with Red Cube Flow set to recommended setting.
72 deg day. Engine was warm at takeoff as I'd just got fuel. WOT 120KIAS climb until CHTs hit about 370 followed by a reduction in power to keep them under 400. IO-360B1B with Sensenich fixed prop. Does an engine need to be at full RPM to benefit the fuel cooling circuit? WOT gets mine hot in a hurry. Maybe it's a timing issue.

Everyone,

Thanks a lot for your kind replys. I spoke with Joe L. at Champion, who is the Lasar expert. He mentioned that the system monitorsthe operation for about 15 minutes for the "climb" portion of operation. During this time the temps can go up to 450-480. If exceeded, the light wil come on but the controller will still be operation. After the initial 15 minutes, the upper temp limit is lowered.

He suggested a breaker to turn off the system to help on climb out. I also saw a note Randy L. posted elsewhere that mentioned he would turn his Lasar off if he encountered high cyl temps on climb out.

Joe also said I may want to retard the TDC setting by one degree.

Again this situation is most noticalbe on less than full power take offs.

Lastly, Joe thought the best thing I can do with an RV-6 is to make sure heat from flying is vented soon after landing. The system has an ambient temp limit around 200 degrees which may easily be exceeded in a tight cowled RV.

Cheers,

Mark

One really late, last reply, I changed the Lasar mags out for one new Slick mag and a P-Mag, a couple of years ago. Temps are a full 30 degrees cooler.

Mark

O-360 Lasar.
WOT. Full rich always when climbing.
I climb at 125-130k IAS.
Works OK.
Less than WOT doesn?t work as well. Seems like the cooling improves considerably at higher speeds and fuel flows.

The venting after landing on a hot day is very important.

LASER was not a commercial success and many people installed them to remove them for high CHT. Why are they worse on CHT historically? I don't know. LASER was an early EI. Now we have so many great choices.