Upgrade to new primary engine monitor but keeping old gauges - CHT probe question

Stephen Shore

Stephen Shore

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sshore
I am getting towards the end of a major project of installing a new factory rebuild Lycoming IO-540 and at the same time installing a new Electronics International CGR-30P engine monitor that is certified as the "primary" monitor BUT I am keeping my old analog gauge cluster as a redundant means of monitoring the engine and fuel.

The CGR-30P of course comes with new bayonet style CHT probes / sensors.

QUESTION: what is the best route to go in regard to a CHT probe for the old analog CHT conventional gauge in the original gauge pack?

I was thinking about using a spark plug gasket type gauge, but I was not sure what type (J or K) or if it made a difference? I realize that the old analog gauge will not be accurate, but after some use, I can determine the delta of it and the reading shown on the CGR-30P as shown for the #5 cylinder and use that ratio if I ever had to rely on the analog gauge for some reason (the failure of the primary CGR-30P unit).

I know that some others have done the exact same thing I have - install a new primary engine monitor but keep the old gauges - so I was looking for a little guidance on the CHT probe for the old gauge.
 
I am not sure what style CHT your analog gauge had, but you could get a spark plug gasket type probe for the CGR for that cylinder.
 
Jesse Saint said:
I am not sure what style CHT your analog gauge had, but you could get a spark plug gasket type probe for the CGR for that cylinder.
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The only problem with that is that the #5 cylinder would read a little differently on the CGR compared to the other cylinders on the CGR, which of course would get their readings from the same style of probe.

I would rather the "different" probe be assigned to the old analog CHT gauge.
 
When I had my JPI 830 installed, the spark plug gasket style probe went to the JPI and the probe for the original gauge was left in place. However, the 830 is not certified for primary so I had no choice. Since your engine monitor is, I would install the probes as Stephen Shore suggests. Otherwise, the engine monitor will show one cylinder off (colder in my case) as compared to the the others.
 
Like others have said, it not good form to mix prob types on a common system. The CGR-30 will not understand why one CHT with a spark plug sensor is 40º higher then the rest.

Why do you want the old analog unit in operation? It's likely inaccurate. The last time it was calibration checked was likely when it was built. Most of them are relative temp without markings. Mask off the gauge with black vinyl and enjoy the digital accuracy of the CGR-30. You are going to want to download data logs from the CRG-30 for engine analysis, consistency is recommended.
 
belbert said:
"A man with a watch knows what time it is. A man with two watches is never sure."

Pull all the analog gauges and don't look back...
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Fair point and I might end up doing that. The engineer in me likes redundancy, even if it is only "relative" in nature.

The thing is, compared to most airplanes I have owned or flown, the Commander "six pack" factory engine gauges are actually very functional in their location and easy to monitor. Plus, I just like the looks of them. It would be a perfect set up in my mind to have those gauges along with a modern graphical engine monitor.

But, if I can't get this worked out, I may just give up and do exactly what has been advised and just put a "blank" over the analog CHT gauge and be done with it.
 
NordicDave said:
Like others have said, it not good form to mix prob types on a common system. The CGR-30 will not understand why one CHT with a spark plug sensor is 40º higher then the rest.

Why do you want the old analog unit in operation? It's likely inaccurate. The last time it was calibration checked was likely when it was built. Most of them are relative temp without markings. Mask off the gauge with black vinyl and enjoy the digital accuracy of the CGR-30. You are going to want to download data logs from the CRG-30 for engine analysis, consistency is recommended.
Click to expand...

Why not? Switching to a spark plug probe on the analog unit will be cheap and easy, and you can calibrate it from the (presumably) more accurate CGR.
 
NavAir said:
Why not? Switching to a spark plug probe on the analog unit will be cheap and easy, and you can calibrate it from the (presumably) more accurate CGR.
Click to expand...
I'd call EI and ask them regarding consequences. The spark plug sensors are not as accurate and not recommended unless special circumstances demand it, let alone mixing probe/sensor types. EI can probably provide the authoritative answer to satisfy the question.
 
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I believe there are double-probes available for the thermowells which allows the factory probe to sit inside the probe for the CGR. Like this one(which admittedly is Insight branded): https://www.aircraftspruce.com/catalog/pnpages/2855.php (Which appears to be Type J, and I think EI needs Type K)

Looks like JPI has a Gasket style that fits under the OEM probe, not under the spark plug for this one: https://www.aircraftspruce.com/catalog/pnpages/10-03689.php


Before I ripped mine out, I had all spark plug CHT probes(My Tanis heater used the thermowells) and they always seemed to eventually be damaged from the spark plug removal and reinstallation.
 
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