Slow to warm cylinder

[Seth]

As many of you know I have recently replaced all six cylinders on my Mooney Missile. It has an IO-550. I've noticed that cylinder number 5 is slow to warm up. It lags behind the other cylinders by 75 degrees or so until a few minutes into the flight and then catches up to a much more forgiving spread. It is still one of my cooler running cylinders. Obviously, during a break in you want to keep your ground time to a minimum before the flight, but I just wanted to know what others may think of this slow to warm cylinder.

It's been about 10 hours now on the clyinders and it is still performing its slow to warm routine. It's cylinder number 5. I'll ask my MSC at Freeway the same question soon, but I'd like your collective wisdom.

EGT is in line with the rest of the cylinders, just the CHT being about 75 degrees low and then once during climb and early in cruise it slowly creeps up to the acceptable spread world.

Thanks,

-Seth

[Marauder]

It sounds like you are seeing all the temps so I am guessing you have an engine analyzer of some sort. It could be something as simple as a bad probe. You could switch probes around and see if it follows the probe.

If EGTs are normal, it is suggesting that normal combustion is happening. That could point to bad baffling around the cylinder (getting much more cooling around that cylinder than the rest.

I guess you could have other internal problems (like poor seating rings), but I will leave it up to the people in the know to comment on these kind of things.

[Seth]

The seating rings is what I'm worried about, as I'm 10 hours into the break in. And yes, I have a JPI 830 - it's a fantastic engine monitor.

My number 2 cylinder is the warmest currently. What cylinder usually is the warmest in the six cylinder engines?

-Seth

[N601RX]

The slow to warm cylinder may be using a different style probe. This is probably the cylinder your factory gauge is on.

Its also possible that the probe on that cylinder isn't in firm contact with the cylinder.

[andrew]

I always have one anomalous CHT on my 830 because the factory gauge requires a different style probe to be used and it has a different response characteristic. I talked with JPI about this when I first installed it, they told me that there is not really a way around this without going to a JPI primary unit. It manifests on mine as the primary instrumented cylinder being consistently about 50-70F cooler than the rest, and looking back through the downloaded log data, it displays a very short time delay (maybe about 20s). I don't normally see this difference change much over time though. If it is actually creeping up with flight time then you may very well have something reducing the thermal conductivity between the cylinder and the probe.

[Marauder]

I always have one anomalous CHT on my 830 because the factory gauge requires a different style probe to be used and it has a different response characteristic. I talked with JPI about this when I first installed it, they told me that there is not really a way around this without going to a JPI primary unit. It manifests on mine as the primary instrumented cylinder being consistently about 50-70F cooler than the rest, and looking back through the downloaded log data, it displays a very short time delay (maybe about 20s). I don't normally see this difference change much over time though. If it is actually creeping up with flight time then you may very well have something reducing the thermal conductivity between the cylinder and the probe.

I thi I know what you are talking about. On my GEM, I had to use a different probe on the cylinder that has the factory required CHT probe. That could explain a difference. Was it different before you had the top overhauled or did you not have the engine analyzer on it?

[carusoam]

According to my POH...

"Cylinder head temperature is controlled by an electrical resistance type temperature probe installed in cylinder number 2."

If you have this, consider getting a new "temperature controller"???

What I get out of this is that the TC is on cyl#2. Keep in mind that the Lycoming engine numbering scheme is opposite from the Continental scheme. Front to back vs. back to front.

How's the 830 working out for you???

Best regards,

-a-

[DonMuncy]

The factory probe is a thermal resistor, which varies the resistance in relation to the temperature, which the gauge reads.

The JPI uses a thermocouple, which generates an electrical charge which the JPI reads.

Do you know where the JPI probe takes its reading. Since the factory gauge is occupying the fitting in the head the JPI (ideally) would use, the JPI "probe" must go somewhere else. Often they install a washer type fitting under one of the spark plugs. The other choice is a smaller washer type fitting placed under the factory probe. I believe these are likely to read a little closer to the temperatures on the other probes than the spark plug types.

The washer type probes are available for non-aviation sources, substantially cheaper.

[carusoam]

Thanks Don!

Learned something new today regarding my Mooney.

Thanks to the MooneySpace Community, as well!

Best regards,

-a-

[jetdriven]

The factory probe is a thermal resistor, which varies the resistance in relation to the temperature, which the gauge reads.

The JPI uses a thermocouple, which generates an electrical charge which the JPI reads.

Do you know where the JPI probe takes its reading. Since the factory gauge is occupying the fitting in the head the JPI (ideally) would use, the JPI "probe" must go somewhere else. Often they install a washer type fitting under one of the spark plugs. The other choice is a smaller washer type fitting placed under the factory probe. I believe these are likely to read a little closer to the temperatures on the other probes than the spark plug types.

The washer type probes are available for non-aviation sources, substantially cheaper.

We have a 3/8 Type J thermocouple under the factory probe in the head. It reads a WAG low, about 20-40 degrees. But its predictable and no messing with spark plug washer thermocouples.

Cost was 9$.