OK so anybody else notice that your EGT temps read about 150 degrees hotter 2 minutes after takeoff than they do every subsequent takeoff? This is confirmed on all three cubs that I fly. 160 HP O-320. I am talking about full power climb-out from any elevation below 4000', with the mixture full rich and auto fuel enrichment functioning properly. I should mention too that I use an electronics international EGT, CHT, OAT and the probe for the EGT is 6" from the cylinder.

Does anybody have any insight on why this is, I actually reduce power and cool down when I start nearing 1400 degrees. Any feed back would be great.

Cheers
Matt Keller
http://blog.blueiceaviation.com/

I'm just making a guess so don't rely on my knowledge here. Maybe the heat doesn't have time to spread to the rest of all that metal by the first takeoff and it's concentrated in the cylinders and a longer warmup is warrented? Okay, somebody either back me up or gong me. LOL

This is just a WAG. Could it be due to the location of the "Cold junction" in the EGT wiring? Maybe the junction location warms up slowly. I think most EGT gauges measure the difference between the probe and the cold end of the wire not actual temp of the probe. 150 degrees seems quite a bit unless the junction is getting quite warm.

Matt,

When it comes to these type of questions about egt/cht, I like to go back and get a tune up on my thinking from the "Pelican's Perch" series of articles at avweb by Mr. John Deakin. Quite informative stuff!

Here's a link

http://www.avweb.com/news/pelican/182179-1.html

May not pertain as much to your non fuel injected engine, but still common sense education about the combustion event.

Cheers.

I don't know if it is true but I have been told that warm water will freeze faster than cold. Sounds like BS to me but if it's true maybe cold steel will transfer heat faster than hot metal will?

XKV8R wrote:Matt,

When it comes to these type of questions about egt/cht, I go back and reference the "Pelican's Perch" series of articles at avweb by Mr. John Deakin. Quite informative stuff!

Here's a link

http://www.avweb.com/news/pelican/182179-1.html

May not pertain as much to your non fuel injected engine, but still common sense education about the combustion event.

Cheers.

Good link! Thanks. GONGGGGG!

Howdy Matt,

I was just wondering what (with the mixture full rich and auto fuel enrichment functioning properly)means, is there some sort of function on your carb that enrichen's the mixture on takeoff. I have heard of derichment on carbs on engines that use water.

Dave

XKV8R wrote:Matt,

Here's a link

http://www.avweb.com/news/pelican/182179-1.html

Thanks a lot dude, I had a bunch of other stuff to do this afternoon, and I just burned some serious time on that Deakin's site ... it's excellent. A wealth of knowledge that will take some time to pick through, but great info for our 185 ops.

TCJ I assumed that the instrument was reading actual temperature, but you may be right about that cold junction and that would be a very logical explanation. I've often wondered if I was actually a skosh leaner on the first flight because of the cold engine. I'm certainly not much of a ground runner, once my cylinder head temps reach 100 degrees I go for it. I will test this at some point; one morning thoroughly warm up the engine, and the next morning do my standard ops and see if there is a difference.

Oh and Dave there is some point around 80% throttle where the carburetor automatically delivers more fuel to the engine. You get the highest EGT when you are climbing at like 79% throttle because the engine is working hard but it has a rather lean mixture. That's why I always climb at full power.

Matt Keller
http://blog.blueiceaviation.com/

Jaerl wrote:I don't know if it is true but I have been told that warm water will freeze faster than cold. Sounds like BS to me but if it's true maybe cold steel will transfer heat faster than hot metal will?

Warm water will not freeze.

Tim

BlueIceAviation wrote:Oh and Dave there is some point around 80% throttle where the carburetor automatically delivers more fuel to the engine. You get the highest EGT when you are climbing at like 79% throttle because the engine is working hard but it has a rather lean mixture. That's why I always climb at full power.

Matt Keller
http://blog.blueiceaviation.com/

Deakin address's this.

Some aircraft have a feature that enriches the mixture at full throttle. Folks that want to be "easy" on their engine and pull the power back slightly might be doing the opposite by unknowingly leaning the engine and increasing cylinder pressures to much.

Alot of us were taught to do this by our primary CFI's. Its one of the many "old wives tales" that he clears up.

qmdv wrote:

Jaerl wrote:I don't know if it is true but I have been told that warm water will freeze faster than cold. Sounds like BS to me but if it's true maybe cold steel will transfer heat faster than hot metal will?

Warm water will not freeze.

Tim

Hi Tim,

I look forward to the Alaska guys chiming in on this. In super cold temps I believe you throw a cup of warm water in the air it may freeze faster than the cold water. Somebody on this forum will set us straight!

HA! You know I have spent some time arguing about this "warm water" bit with my friend Zach Steer who is a dog musher (currently 14th on the Iditarod Trail). He heats up water and then dumps it into the dogs food bowls. I've helped him with this miserable process and I always tell him, "you know hot water freezes faster than cold" and he say "bull" and I says, "no really" and so on and so forth. So the above comment prompted me to finally google it and here is what I found. It's called the Mpemba effect ... no seriously. Oh' ya and I have thrown the cup of cold water in the air at -30 and no ... nothing comes down.

http://math.ucr.edu/home/baez/physics/G ... water.html

Matt Keller
http://blog.blueiceaviation.com/

Well, there you have it. If it works for water molecules, why wouldn't it work for metal molecules? And if it works for cooling why wouldn't it work for heating.

Or,,, it could be that the cooler air going into the engine when it is cold is denser and the denser air pulls more fuel/air mixture. More fuel, more heat. Just like a Turbo can make the same engine have more power and burn more fuel, denser air should do the same although on a much smaller scale.

It's like a good book. If you don't want to be up late into the night the next couple of nights, don't follow the provided link.

Cheers/enjoy!

BlueIceAviation wrote:Does anybody have any insight on why this is, I actually reduce power and cool down when I start nearing 1400 degrees. Any feed back would be great.

Cheers
Matt Keller
http://blog.blueiceaviation.com/

Cylinder pressures and CHT's are what's to be of concern. High EGT's are as controversial as LOP operations.

CHT's correlate closely with Cylinder Pressure.

The greater the pressures the more wear and tear.

In the Lyc the carb discharges the air and wet fuel into the spider in the oil pan. The cold oil vs the hot oil would not allow the wet fuel to vaporize as well during the first flight. The unvaporized fuel would show a leaner condition on egts. Just like needing choke on a cold Ford truck.

Warm water does not freeze faster than cold.
However if you fill an container with warm water to a specific volume and one with cold water to the same volume you will find that when the warm water cools to the same temperature as the cold water that there is slightly less water in the container. Similar to density altitude. So in essence you are freezing a smaller volume of water in the warm water container.
With all factors the same, the cold water definitely freezes faster than warm because it already has a head start!
Should now be clear as mud.

tcj wrote:This is just a WAG. Could it be due to the location of the "Cold junction" in the EGT wiring? Maybe the junction location warms up slowly. I think most EGT gauges measure the difference between the probe and the cold end of the wire not actual temp of the probe. 150 degrees seems quite a bit unless the junction is getting quite warm.

OK so I've learned that this Electronics International instrument is a pure thermocouple. For every degree of temperature rise there is something like a 23 millivolt change. That voltage is calibrated and reads on my dash as an actual temperature. If I stick it in a glass of boiling water it should read 212 degrees.

Skydive206 I think you nailed it, the colder oil results in less atomization of fuel leaving the mixture slightly leaner on the first operation of the day, that makes perfect sense. Thanks for help guys.

Matt Keller
http://blog.blueiceaviation.com/

I have a o-235 that I put Electronic Fuel injection on. I have a sensor that measures the induction air temp. After the divider in the oil pan and the oil raises the air fuel mixture temp 10 deg f above ambient. Ive ran that engine carburated on E-85 and it just loves Alcohol. 150 hp at 3200 rpm and 15 gph. Hearing it purr you couldnt believe that it used to be a 152 engine. This engine has JPI with ff and electronic ignition.