Cylinder temperature

[Werner]

Hello, I notice that the two rear cylinders run hotter than the two from front. The compression on all 4 cylinders is nearly equal to 4 kg / cm.

Is my guess right, that the rear cylinders get less fuel mixture and therefore runs leaner and hotter?

[wmws]

I think it is more the fact of water circulation in the block. The rear cylinder seems to get short changed because the pump is trying to pull the water forward.

[rotorwrench]

Yep, with feed in the center of the block and exit at the front, the circulation at the back is a bit lacking. They've been working this way for 90 years or so.

[Synchro909]

I've seen pictures of an engine where a hose was taaken from the water return fitting at the side of the block to the rear of the block, thus getting cool water to cylinders 3 and 4.

[Mike Peters]

Another thing...since the engine is tilted slightly to the rear, rust in the water jacket will tend to collect in the rear more than the front, thus restricting circulation to a degree. I recently pulled an engine apart for inspection and found lots of crud in the #3 and 4 water jacket, and very little in the two front cylinders.

[Kurt in NJ]

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I was curious after reading the posts about the temp differences and checked my car and found that the area around #4 ran cooler than #2, by 3 degrees after 1 hour idling on 90 degree day, but #4 was only only 1 degree warmer than #2 after pulling over from a few miles driving over 60---and that driving fast on the bumpiest road I could find didn't make the shocks heat up more than 2 degrees
----35 years after cleaning the block and radiator, always used antifreeze

[Tom Wesenberg]

I checked my block a few years ago and my readings were just as Kurt found.

[History]

Does anyone use an exhaust gas temperature gauge on their A? I know it's important in small aircraft as you lean and enrich the gas depending on altitude. It can save you from frying an engine. I know it's not necessary but figured someone has done it??

[Werner]

Hallo History, I have something as a handheld device. I need that for the small methanol aircraft engines. But this is not useful for an absolute measurement, since the temperature in the exhaust stream is very different. It is only right in the middle of the gas stream directly behind the exhaust valve. What you need is a stationary installation of the temperature sensors for each cylinder.

[Werner]

Hallo to each other. Thank you for the many hints. That the cylinder temperature is higher behind than the front, I have not measured, but recognized by the spark plug face.

Because of your advice, I have just mounted transparent measuring spark plugs (glass insulator). The two rear cylinders run visibly leaner, the color of the ignition flame is lighter blue.

Therefore the reason seems not to be the water circulation, but the uneven fuel distribution.

I put in the back experimantaly spark plugs with 1 number higher working temperature and will continue the observe.

[BRENT in 10-uh-C]

Originally Posted by History

Does anyone use an exhaust gas temperature gauge on their A? I know it's important in small aircraft as you lean and enrich the gas depending on altitude. It can save you from frying an engine. I know it's not necessary but figured someone has done it??

Generally this is two different operating conditions. The aero engine is air cooled generally with a tightly shrouded top-end whereas the A engine is water-cooled and in a much less shrouded environment. Also, the aero is running at a tighter margin of horsepower whereas the typical A engine may only be at 75% at higher speeds.




Also something to factor in is that the water inlet is coming in between the #2 & #3 cylinders. Because of the siamesed intake ports, and the firing order being 1243, the #2 and #3 cylinders will be most affected by a lean fuel mixture since the #2 cylinder only gets what is left over in the intake that #1 did not use, and the same applies for #3 getting "left-overs" from the #4 cylinder. Therefore fuel mixture has little to do with #4 running hot(ter).



My experiences of loose rust in the jacket area has little effect either. The rust settlement will be located at the lowest area of the heated water and since the majority of the heat in the cooling system is in the cylinder head (combustion heat rises in an F-head) followed by the exhaust ports, the water is able to dissipate heat. It really is not the water flowing that removes the heat. For those around 'hit & miss' engines will understand how the water hopper surrounds the metal and dissipates the heat well even when the engine is under a strong load and making large amounts of combustion heat. Something I think that many get caught-up in is the panic when they see steam rising. The only time steam is a bad thing is when steam pockets are created in the water jackets next to the cylinder wall or roof of the head as the steam will push surrounding water away from the surface which then stops the heat dissipation into the water. People tend to panic when a Model-A engine gets over 180°, -yet in our race engines we don't get excited until we are running engine water temps in excess of 230°. Even Model-T engines run better with engine temps in the 200°+ range.


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[rotorwrench]

EGT monitoring is important when leaning for altitude on an aircraft engine plus an air cooled engine is more sensitive to temperature variations than a liquid cooled engine. It wouldn't be all that practical for a liquid cooled automobile engine since an air fuel ratio meter would likely tell a person more for them. It would be easier to adapt for sure.