Exhaust Manifold Temperatures

[2510Paul]

My son and I started the engine we re-did in our JD 2520 diesel. I used one of those laser target non-contact thermometers and noticed the exhaust Manifold temperatures varied by cylinder. Two were the same and the other two were high and low by about 15F. I don't recall the exact numbers so I won't repeat them here. One injector line had a leak, the lowest temp., so I am thinking that might be contributing.

Today I started my JD 2510 diesel and let it run for a while and took the temperatures on the exhaust manifold and recorded them.
#1 226 F
#2 247 F
#3 225 F
#4 200 F

Can anyone tell me what is a normal variation in these temperatures? Does anyone know the source of the variation? Might it be how much fuel is being pumped into that cylindar? Again, these are the tempertures on the surface of the exhaust manifold directly opposit the exhaust port in the head. Paul

 

[PopinJohn]

As stated, these are surface temps of the manifold, and from what is written, they were not taken while the engine was at speed and under load. I would think you need more information.
For a more specific analysis, suspecting a problem in a cylinder, a temp probe in the same location in each port would be better.
Exhaust temps are a result of spent gases (obvious) that are influenced by a combination of factors such as specific intake air flow to the cylinder, specific fuel injected, lubricating oil that passes into the combustion chamber, and the shape of the exhaust manifold (center or end outlet).
And fuel injection pumps are usually calibrated at a high RPM, (such as 1800) not at low speeds. Also, popping pressure of injectors are not always matched to sets, so you could have one in four that is on the low end of the spec, and one that is on the high end of specification, but all four are considered "normal".

 

[DONMYEIL]

I think you are worried about something that doesn't matter .

 

[Hotflashjr]

To spin this in a whole different direction, those guns are not accurate by any means. We have been using them on cranberry bogs to get temperature readings for some research we are doing. We also have bulb thermometers and temp probes on the bogs. The hand held laser guns have varied as much as 10-15 degrees. We found the longer you hold it in your hand the higher the variation. Point it at the same spot and click it 5 times in a row and it will surely read different and with more variance each time. Ended up getting 5 of these all of different age and maker together to see if we could find one that was the "odd man out" and could not. They each did the same thing with only one being better than the others but by better I mean a few degrees less in variance. Just had to toss this in there as well!

 

[Texasmark1]

......and there are different external heat sinks on each cylinder output changing the readings. The thermometer is a cone sensor and the distance from the object and angle of exposure determines the size of the sample area which impacts the reading on small items and an exhaust manifold can be considered a small item especially when you are looking at the difference in the cylinder outputs. Your hand on the instrument is modifying the external ambient temp which the instrument surely uses in it's temperature determination unless a more sophisticated instrument that has internal temperature stabilization.

On accuracy, 10 degr out of 200 is 5%. Pretty good tolerance for most instruments (scientific excluded). For what you are measuring 20% tolerance is probably more than you need.

HTH,

Mark

 

[AF 70]

I had uneven firing on my gas 2-banger and did same thing you did, only was reading from the "riser" on the cylinder head to which the manifold was bolted. One side was 300* lower than the other, which turned out to be a valve starting to go. I agree that the differences you are seeing are not indicative of a problem. I also agree that the non-contact thermometers are probably not all that accurate, but are good to compare "this" to "that".

 

[WJD]

15 deg. is not a lot. Lots of things can cause this, thickness of cast iron, length of exhaust runner, etc. I would not lose any sleep over 15 deg.
I assume this is under load. Loaded temps. are more important than idle temps. As my former boss would say if it was measured cold and under a light load...go do it again.